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Journal of Human Evolution 65 (2013) 109e142

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Journal of Human Evolution

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Systematics of Paleogene Micromomyidae (Euarchonta, Primates)from North America

Stephen G.B. Chester a,*, Jonathan I. Bloch b

aDepartment of Anthropology, Yale University, P. O. Box 208277, New Haven, CT 06520, USAb Florida Museum of Natural History, University of Florida, P. O. Box 117800, Gainesville, FL 32611-7800, USA

a r t i c l e i n f o

Article history:Received 21 September 2012Accepted 23 April 2013Available online 12 July 2013

Keywords:EuarchontanMicromomyidPlesiadapiformPrimate originsLate PaleoceneEarly Eocene

* Corresponding author.E-mail addresses: stephen.chester@yale.edu

flmnh.ufl.edu (J.I. Bloch).

0047-2484/$ e see front matter � 2013 Elsevier Ltd.http://dx.doi.org/10.1016/j.jhevol.2013.04.006

a b s t r a c t

New specimens of micromomyid plesiadapiforms recovered from the late Paleocene and early Eocene ofthe Clarks Fork and Powder River Basins, Wyoming, include previously unknown tooth positions ofChalicomomys antelucanus, the earliest record and first substantial Paleocene sample of Tinimomysgraybulliensis, and additional specimens of early Eocene T. graybulliensis, forming the largest knownsample (n ¼ 84, MNI ¼ 14) of a micromomyid species from a single fossil locality. These specimens andnewly documented intraspecific variability, coupled with the first detailed descriptions of the dentitionof Dryomomys szalayi, allow for a systematic revision of the family. Cladistic analysis of the 11 knownmicromomyid species using 28 morphological characters produced three most-parsimonious clado-grams. Results suggest that several Tiffanian taxa previously classified in the genus Micromomys(excluding the type species Micromomys silvercouleei) are more primitive and are referred to a new genusFoxomomys (Foxomomys fremdi, Foxomomys vossae, and Foxomomys gunnelli). Two other Paleocene andearly Eocene species previously classified inMicromomys are instead found to share a special relationshipwith Dryomomys (Dryomomys millennius and Dryomomys willwoodensis) based primarily on the relativesize and shape of the premolars. Results further suggest that early Eocene Chalicomomys (monotypic:Chalicomomys antelucanus) is the sister taxon to a clade that includes Dryomomys and Tinimomys, whichdiverged from each other by the late Tiffanian. The shape of P4 and the relative size of P3 have distinctpatterns of change through the evolution of the group. Additionally, there is a gradual reduction of P2,with Foxomomys having a double-rooted P2, Micromomys, Chalicomomys, and Dryomomys having asingle-rooted P2, and Tinimomys lacking a P2. Body size increases from more primitive micromomyids(Foxomomys and Chalicomomys) to more derived genera (Dryomomys and Tinimomys), and size also in-creases from the older and/or more primitive species within the Dryomomys and Tinimomys lineages.

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Introduction

Micromomyid plesiadapiforms are diminutive euarchontanmammals known from the late Paleocene (middle Tiffanian NorthAmerican Land Mammal Age (NALMA)) to the early Eocene (earlyWasatchian NALMA) of western North America (Szalay, 1973, 1974;Bown and Rose, 1976; Krause, 1978; Bown, 1979; Rose, 1981; Roseand Bown, 1982; Fox, 1984; Gingerich, 1987; Beard, 1989, 1993a;Beard and Houde, 1989; Gunnell, 1989; Rose et al., 1993; Robinson,1994; Wilf et al., 1998; Bloch, 2001; Strait, 2001; Bloch et al., 2007;Secord, 2008; Chester and Beard, 2012; Fig. 1, SupplementaryTable 1). More specifically, micromomyids have been found in

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three NALMAs including the Tiffanian (faunal zones Ti-3eTi-5b)and succeeding Clarkforkian (Cf-1eCf-3) of the late Paleocene, andthe Wasatchian (Wa-1eWa-2) of the early Eocene. Outside NorthAmerica, only an undescribed dentary from the early Eocene Wutufauna, Shandong Province, China (Tong and Wang, 1998) hastentatively been referred to Micromomyidae.

Micromomyidae is generally considered a monophyletic group(e.g., Beard and Houde, 1989; Silcox, 2001) and these ‘plesiadapi-forms’ (also referred to as ‘archaic primates’) are recognized in partby their large, specialized fourth premolars, and very small bodysize (Silcox and Gunnell, 2008). The first known micromomyids,Micromomys and Tinimomys, were originally thought to be closelyrelated to archaic primates similar to Plesiolestes, Palaechthon, andPalenochtha, and were therefore referred to the Paromomyidae(sensu lato; Szalay, 1973, 1974). Subsequent studies essentiallyagreed with these proposed relationships, but classified Microm-omys and Tinimomys in the family Microsyopidae (Bown and Rose,

Institutional abbreviations

CM Carnegie Museum of Natural History, Pittsburgh,Pennsylvania, U.S.A.

UALVP University of Alberta Laboratory for VertebratePaleontology, Edmonton, Alberta, Canada

UCM University of Colorado Museum, Boulder, Colorado,U.S.A.

UCMP University of California Museum of Paleontology,Berkeley, California, U.S.A.

UM University of Michigan Museum of Paleontology,Ann Arbor, Michigan, U.S.A.

USNM National Museum of Natural History, SmithsonianInstitution, Washington, D.C., U.S.A.

USGS United States Geological Survey, Denver, Colorado,U.S.A.

UW Geological Museum, University of Wyoming,Laramie, Wyoming, U.S.A.

YPM-PU Princeton collection at Yale Peabody Museum, NewHaven, Connecticut, U.S.A.

S.G.B. Chester, J.I. Bloch / Journal of Human Evolution 65 (2013) 109e142110

1976; Krause, 1978; Fox, 1984; Gunnell, 1989; but see Gingerich,1976; Szalay and Delson, 1979). Fox (1984) suggested that theoldest known micromomyid, Micromomys fremdi, was a micro-syopid most closely related to Purgatorius and Palenochtha minor.Additional evidence supported classification of micromomyidsamong themost primitive plesiadapiforms including the oldest andmost primitive taxon Purgatorius (e.g., Beard and Houde, 1989; VanValen, 1994; Silcox, 2001). Recent observations that tarsals of Pur-gatorius are uniquely similar to those of micromomyids also suggestthat micromomyids are among the most basal primates (Chesteret al., 2012).

Figure 1. Map of fossil localities where micromomyid plesiadapiforms have beenfound. (A) UADW-2, Paskapoo Formation, Alberta (Foxomomys fremdi); (B) UAR2a andUAR2, Roche Percee local fauna, Ravenscrag Formation, Saskatchewan (F. vossae); (C)Polecat Bench region, Bighorn Basin, Wyoming: Silver Coulee beds, Fort Union For-mation: Princeton Quarry (Micromomys silvercouleei), Y2K Quarry (Dryomomys mil-lennius), and Schaff Quarry (F. gunnelli); and Sand Coulee localities: Fort Union andWillwood Formations (D. willwoodensis, Chalicomomys antelucanus, Tinimomys gray-bulliensis, D. szalayi); (D) No Water Creek area, Willwood Formation, Bighorn Basin,Wyoming (T. graybulliensis); (E) Powder River Basin localities, Wasatch Formation,Wyoming (C. antelucanus, T. graybulliensis, ‘Myrmekomomys loomisi’); (F) Big MultiQuarry, Washakie Basin, Wyoming (D. dulcifer and T. tribos).

Along with other plesiadapiforms, micromomyids have tradi-tionally been recognized as being more closely related to crownclade Primates than to other euarchontan mammals (i.e., Scan-dentia and Dermoptera). In contrast, Beard (1989, 1990, 1993a,b)suggested that micromomyid and paromomyid plesiadapiformsshare unique postcranial features associated with mitten-gliding inextant flying lemurs and classified these extinct families in Der-moptera. More recent discoveries of partial skeletons of paromo-myids and micromomyids, coupled with new phylogeneticanalyses usingmorphological data from the dentition, cranium, andpostcranium, do not support this hypothesis and instead suggestthat they are primitive stem primates (Bloch et al., 2007; Silcoxet al., 2010; Fig. 2) that did not glide (Boyer and Bloch, 2008).

Micromomyids have a reduced dental formula (2.1.3.3/1.1.2-3.3)suggesting that in this respect they are not as primitive as someother plesiadapiforms, such as Purgatorius janisae (lower dentalformula: 3.1.4.3). Nevertheless, with complete dentitions, partialcrania, and most of the postcranium recovered, micromomyids arethe best known of the most primitive stem primates (Fig. 2).Micromomyidae is represented by 11 species that span approxi-mately five million years. A clear understanding of relationshipswithin Micromomyidae allows for a better understanding of whatmight be considered primitive not only for the clade, but for earlyprimates in general. As primitive euarchontans (and likely stemprimates), micromomyids share a relatively recent commonancestry with euprimates (crown clade primates), were arboreal insome ways like the earliest euprimates, overlap temporally withthe first documented euprimates, were fairly similar in size to someof the earliest known euprimates (e.g., Altanius, Altiatlasius, Teil-hardina), and had similar dental characteristics such as low-crowned molars with bunodont cusps. A revised phylogeny andbetter understanding of the ecological significance of the distinc-tive morphological features of micromomyids may also provide aclearer view of the ecological changes characterizing the evolutionof the earliest euprimates.

Figure 2. Hypotheses of evolutionary relationships of micromomyids and othereutherian mammals. (A) Simplified resulting single-most-parsimonious cladogrammodified from Bloch et al. (2007) with micromomyids as the most basal primates otherthan Purgatorius. (B) Simplified resulting strict consensus cladogram modified fromSilcox et al. (2010) with a clade consisting of micromomyids and microsyopids as themost basal primates other than Purgatorius. Note that these analyses support thesupraordinal group Euarchonta with Sundatheria (Scandentia and Dermoptera) as thesister taxon to Primates, and plesiadapiforms as stem primates. Micromomyid imagemodified from Bloch et al. (2007).

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Eleven species of micromomyids have been classified in fivegenera (Micromomys, Tinimomys, Chalicomomys, Myrmekomomys,Dryomomys). Species-level alpha taxonomy of micromomyids iscomplicated by the fact that four of the 12 proposed species areonly represented by their respective holotype, and three of the 12species proposed are only each represented by two specimens. Ithas been suggested that Micromomyidae suffers from over-splitting, absent an understanding of intraspecific morphologicalvariability (e.g., Rose and Bown, 1996). Here we report 54 newspecimens of early Eocene Tinimomys graybulliensis from the ClarksFork Basin, Wyoming, which add to the largest sample of anymicromomyid species from one fossil locality (84 dental specimens,MNI ¼ 14). Newly documented morphological variability allows formore accurate diagnoses of micromomyid taxa. Additional de-scriptions of new micromomyid specimens from the Clarks Forkand Powder River Basins, Wyoming, including the first detaileddental descriptions of Dryomomys szalayi and a cladistic analysis ofdental and gnathic characteristics that includes all recognizedspecies of micromomyids, allows for a systematic revision of thisfamily.

Materials and methods

All species and most specimens previously attributed toMicromomyidaewere analyzed in this study (see Appendix A). Newspecimens including a premolar of Dryomomys sp., five specimensof Chalicomomys antelucanus, and 14 Clarkforkian specimens ofT. graybulliensis are described. Fifty-four new early Eocene (Wa-1)specimens of T. graybulliensis are reported from UM locality SC-4.These specimens were previously recovered by etching fresh-water limestone blocks from the Fort Union and Willwood For-mations of the Clarks Fork Basin, Park County, Wyoming (see Bloch,2001; Bloch and Boyer, 2001). Eight new specimens ofT. graybulliensis from the Wasatch Formation of the Powder RiverBasin, Wyoming, are also described.

Figure 3. Dental and gnathic measurements of micromomyid specimens recorded using Acalipers under a microscope (following in part Rose, 1975; Bloch and Gingerich, 1998). Micro-I2eM3 in occlusal view; (B) I1 in occlusal (left) and buccal (right) views; (C) I1eM3 in occluLength (L) measures maximum mesiodistal dimensions and width (W) measures maximumbase of the enameledentin junction to the apex of the crown, and P4 H measures lingual sidemoderately exodaenodont on buccal side). Mandibular depth (MD) measures below distal

Specimens were micro-CT scanned at 6e10 microns on a ScancoMedical mCT 35 machine at Yale University. Three-dimensionaldigital reconstructions were created and measured using Avizo 6software (http://www.vsg3d.com/avizo). In the rare case that aspecimen such as a holotype could not be acquired on loan for CTscanning, either a cast was scanned, or the specimen or a cast wasmeasured using digital calipers under a microscope. Measurementsinclude maximum mesiodistal length (L), maximum buccolingualwidth (W), and P4 crown height (H) (see Fig. 3; Appendix A). Digitalphotographs were taken using a Visionary Digital (Palmyra, Vir-ginia) setup with Canon 40D and 5D cameras at the FloridaMuseum of Natural History.

To assess relationships among species of micromomyids, a ma-trix including 13 taxa and 28 dental and gnathic characters (seeAppendix B) was assembled in MacClade 4.06 (Maddison andMaddison, 2003). Cranial and postcranial characters were notincluded because dentally associated cranial and postcranial ele-ments are only known for two species (T. graybulliensis andD. szalayi).

Cladistic analysis included the 11 species of micromomyidsrecognized in this study with Ptilocercus lowii and P. janisae asoutgroups. P. lowii is the most basally divergent extant treeshrewbased on morphological and molecular evidence (e.g., Sargis, 2001,2002a,b; Olson et al., 2005; Roberts et al., 2011) and was used toroot the analysis. Purgatorius was chosen because it is clearlyoutside the ingroup and it is themost primitive plesiadapiform. Thespecies P. janisaewas selected because it is the best-known speciesof Purgatorius and can be scored for 25 of 28 characters in thisanalysis. Although Purgatorius coracis (Fox and Scott, 2011) mayrepresent the most primitive species of Purgatorius known, only 12of 28 characters in this analysis can be scored for this species, andthese 12 characters would be scored exactly as those for P. janisae.Similarly, Purgatorius ceratops is only represented by one isolatedlower molar, can only be scored for four characters, and is notconsidered here. Purgatorius unio was also considered (with

vizo 6 software on three-dimensional micro-CT scan reconstructions or using digitalCT scan images of Dryomomys szalayi (UM 41870) dentition captured using Avizo 6: (A)sal view; (D) I1eM3 and portion of dentary in buccal view; and (E) P4 in lingual view.crown dimensions perpendicular to length. Height (H) of incisors measures from thebetween mesial and distal roots to the apex of the crown (as micromomyid P4s can be

root of P4.

S.G.B. Chester, J.I. Bloch / Journal of Human Evolution 65 (2013) 109e142112

Purgatorius titusi viewed as a junior synonym of P. unio) because itmay be more primitive than P. janisae. Again, fewer characterscould be scored (17 of 28) than for P. janisae, and only one characterin this analysis (P4 paraconid) could potentially be scored differ-ently for P. unio. An analysis was run with Ptilocercus and P. unio asoutgroup taxa, and the tree topology remained the same. Species ofPurgatorius other than P. janisae are not included in the analysis tominimize the amount of missing data present in the matrix. Abranch and bound search was conducted in PAUP* 4.0b10 forMacintosh PPC (Swofford, 2003). All characters were treated asunordered, no characters were weighted, and multistate characterswere interpreted as polymorphic. Most of the characters used inthis cladistic analysis were created for this study, and severalcharacters were modified from Silcox (2001).

Tooth homology and lower dental formula of theMicromomyidae

Krause (1978) documented the presence of five alveoli be-tween I1eP4 in Foxomomys vossae (lower dental formula of 2.1.3.3;Ti-4). He suggested the presence of a double-rooted P3, a single-rooted P2, a single-rooted C1, and a single-rooted I2. Based onmore complete material of Foxomomys fremdi (Ti-3), and bycomparison to Purgatorius (Pu-2-3; Clemens, 1974), the lowerdental formula of F. fremdi and by inference F. vossae, was inter-preted by Fox (1984) to have been 1.1.3.3, with a double-rooted P2.This interpretation is supported through the comparison of themesial part of the dentary of P. janisae (Pu-2-3; Clemens, 2004).Recently published Foxomomys gunnelli (Ti-5a; Secord, 2008) hasan identical inferred dental formula to both F. vossae and F. fremdi,also with an apparent double-rooted P2 in separate alveoli (fivealveoli between I1eP4).

Figure 4. Comparison of lower dental formula between Micromomys silvercouleei (AeC) andentary P4, M2, sectioned along sagittal plane and portrayed in buccal view (A), and three dimand occlusal view (C). C. antelucanus, USNM 512221, L dentary M1e2, sectioned along sagitta512221 were captured using Avizo 6 in buccal view (E), and occlusal view (F). White lines

Beard and Houde (1989) cited the double-rooted condition of P2in F. fremdi as a character that can be used to distinguish the sub-tribe Micromomyina (i.e., Foxomomys and Micromomys silver-couleei) from the subtribe Tinimomyina (Tinimomys andChalicomomys). However, Secord (2008) noted that M. silvercouleeiappears to have a single-rooted P2 like that of Chalicomomys. Here,using micro-CT scans, we show that M. silvercouleei, the type spe-cies of Micromomys known from Princeton Quarry (Ti-5a), andC. antelucanus (Wa-1; Beard and Houde, 1989) have only fouralveoli between I1eP4 (Fig. 4). The two distal-most alveoli inM. silvercouleei are interpreted here as those for a double-rooted P3as in the holotype of C. antelucanus. Mesially, the next alveoluswould have contained a single-rooted P2. The mesial-most post-incisor alveolus appeared to have contained a slightly procumbent,single-rooted canine in both taxa. Secord (2008) further suggestedthat the P2 alveolus in the holotype C. antelucanusmay be relativelysmaller than that of M. silvercouleei and may represent a moreprogressive condition. Though this observation is correct for theholotype of C. antelucanus, the P2 alveolus in a new dentary ofC. antelucanus (UM 512221; Fig. 4) is larger than that of the holo-type, and as large as that of M. silvercouleei.

D. szalayi (Cf-3) is similar toM. silvercouleei and C. antelucanus inthe number, size, and position of alveoli between I1eP4 (Fig. 3D).Thus, we interpret the lower dental formula of D. szalayi to also be1.1.3.3. In contrast, T. graybulliensis (Cf-1 through Wa-2) has adouble-rooted P3, a single-rooted canine, and has lost its P2completely (lower dental formula: 1.1.2.3). We suggest that there isa gradual reduction in P2 size from a distinct double-rooted tooth inF. fremdi, F. vossae, and F. gunnelli, to a reduced single-rooted crownin M. silvercouleei, C. antelucanus, and D. szalayi, to complete loss ofthe tooth in T. graybulliensis. This interpretation lends furthersupport to the hypothesized homology of mesial-most post-incisor

d Chalicomomys antelucanus (DeF). Micro-CT slice of M. silvercouleei, YPM-PU 17676, Rensional scan images of YPM-PU 17676 were captured using Avizo 6 in buccal view (B),l plane and portrayed in buccal view (D), and three dimensional scan images of USNM(C, F) indicate location of CT slice shown in A and D, respectively. Scale bar ¼ 1 mm.

S.G.B. Chester, J.I. Bloch / Journal of Human Evolution 65 (2013) 109e142 113

tooth position as ‘C1’ rather than ‘P2’ in Tinimomys. Neither Dry-omomys willwoodensis nor Dryomomys millennius are preservedwell enough to reconstruct the dental formula mesial to thedouble-rooted P3.

Systematic paleontology

Order: Primates Linnaeus, 1758Family: Micromomyidae Szalay, 1974

Type genus: Micromomys Szalay, 1973Included genera: Micromomys, Foxomomys, Dryomomys, Chali-

comomys, Tinimomys.Diagnosis: Differs from all other plesiadapiforms in having P4

with a trenchant paracristid. Further differs from all other plesia-dapiforms except some species of picromomyids, uintasoricinemicrosyopids, and toliapinids in being very small (M1length ¼ w1.00e1.25 mm). Further differs from Purgatorius inhaving one lower incisor (instead of three), lacking P1, and having arelatively larger P4 than M1. Further differs from palaechthonids inlacking a pronounced postprotocingulum on upper molars. Furtherdiffers from picromomyids in having a smaller P4 talonid with ahypoflexid and more lingually oriented cristid obliqua, and lowermolars with less mesiodistally compressed trigonids compared tooverall length of the crown. Further differs from microsyopids inlacking a lanceolate I1, lacking closely approximated entoconid andhypoconulid on lower molars, and further differs from uintasor-icine microsyopids in having a double-rooted P3 with the mesialand distal roots clearly separated, lower molars with distinct par-aconids, P4 with a metacone, and unreduced upper and lower thirdmolars. Further differs from toliapinids in having lowermolars witha weaker postmetacristid.

Discussion: Szalay (1974) erected Micromomyini and placedM. silvercouleei and T. graybulliensis in this tribe within Paromo-myidae. Gunnell (1989) later elevated Micromomyini to the sub-family Micromomyinae within Microsyopidae and provided aformal diagnosis. Beard (1989) elevatedMicromomyidae to a familylevel in his doctoral dissertation, but did not provide a formaldiagnosis for the new rank there or in subsequent publications (e.g.,Beard, 1993a,b; Rose et al., 1993). Therefore, the differential diag-nosis presented here is the first diagnosis for the familyMicromomyidae.

Foxomomys gen. nov. (Micromomys in part Krause, 1978; Fox,1984; Secord, 2008)

Type species: F. fremdi (Fox, 1984)Included species: F. fremdi (Fox, 1984), F. vossae (Krause, 1978),

and F. gunnelli (Secord, 2008).Known distribution: Late Paleocene of North America (middle-

late Tiffanian NALMA of Saskatchewan (Ti-3) and Alberta (Ti-4),Canada; late Tiffanian (Ti-5a) of the Bighorn Basin, Wyoming).

Diagnosis: Differs from all other micromomyids in havingdouble-rooted P2, narrower P4 relative to length with a cristidobliqua that climbs the postvallid for a short distance, narrowerlower molars relative to length with a protoconid that is consid-erably taller than the metaconid (rather than subequal in height),smaller P3 relative to size of upper molars, P4 with a more dis-tobuccally positioned metacone relative to the paracone on a moreobliquely oriented metacrista, more transversely elongate,triangular-shaped, upper molars with a deeper ectoflexus, andmore acute molar cusps. Further differs from all micromomyidsexcept Chalicomomys in having a relatively more transverselyelongate M2 compared with M1.

Etymology: Named for Richard C. Fox, who described the typespecies, and in recognition of his contributions to our under-standing of plesiadapiforms and other Paleogene mammals. Suffix

omomys by analogy with Micromomys and to suggest primate af-finities of the genus.

Discussion: The genus Foxomomys is erected to reflect differ-ences between the oldest micromomyid species, F. fremdi, andother micromomyids, including the type species of Micromomys,M. silvercouleei. Two poorly known Tiffanian species, F. vossae andF. gunnelli, are tentatively assigned to this genus. The only charac-ters that are clearly unique to all three species of Foxomomys amongmicromomyids are also present in Purgatorius, and thereforeappear to be plesiomorphic. Consequently, like the genus Purga-torius, it is possible that Foxomomys may represent a paraphyleticgrouping. However, unlike the previous state of the genusMicromomys, there is no evidence that Foxomomys is polyphyletic,and current evidence suggests that M. silvercouleei is more closelyrelated to other micromomyids than to F. fremdi, F. vossae, andF. gunnelli (see below). F. fremdi differs from Purgatorius and othermicromomyids in having a relatively higher protoconid than met-aconid on its lower molars. F. vossae appears similar to F. fremdi inthis regard, although it is only known from M1, and molars are notknown for F. gunnelli. Additionally, F. fremdi and F. gunnelli areunique compared with Purgatorius and other micromomyids in theposition of the mesial mental foramen under the distal root of P2(not known for F. vossae). F. vossae and F. gunnelli remain very poorlyknown, and additional specimens are needed to evaluate whetherthese characters are synapomorphies for a Foxomomys clade. Thisgrouping is in agreement with the previous suggestion that it maybe appropriate to place F. fremdi and F. gunnelli in a separate genusbecause M. silvercouleei, C. antelucanus, and D. millennius appearmore derived (Secord, 2008).

F. fremdi (Fox, 1984) (Fig. 5AeE)Holotype: UA 21010, L partial dentary I1 alveolus, crowns of C1e

M3.Known distribution: Middle Tiffanian (Ti-3) UADW-2, Paskapoo

Formation, Alberta, Canada.Emended diagnosis: Differs from other species of Foxomomys in

being slightly larger. Further differs from F. vossae in having P4 witha uniformly sloping mesiodorsal margin in buccal view and one ortwo (rather than three poorly defined) talonid cusps. Further differsfrom F. gunnelli in having a diastema between C1 and P2, and anarrower P4 relative to length.

Discussion: Scott (2008) reported several new specimens ofF. fremdi from the type locality. He described what appears to be thefirst upper canine known for the species, which is larger than P2,unlike the condition present in D. szalayi. Scott also described a newspecimen that has a slightly larger and more transverse P3e4 thanthe only previously known specimen for which these tooth loci arewell preserved.

F. vossae (Krause, 1978) (Fig. 5FeH)Holotype: UA 9273, L partial dentary P4eM1.Known distribution: Late Tiffanian (Ti-4) UAR2, Ravenscrag

Formation, Saskatchewan, Canada.Emended diagnosis: Differs from other species of Foxomomys in

having P4 with a more distinctive break in slope along the mesio-dorsal margin in buccal view, and three poorly defined talonidcusps rather than one or two. Further differs from F. fremdi in beingslightly smaller. Further differs from F. gunnelli in having a narrowerP4 relative to length.

F. gunnelli (Secord, 2008) (Fig. 5IeK)Holotype: UM 77528, L partial dentary P4.Known distribution: Late Tiffanian (Ti-5a), Schaff Quarry,

northern Bighorn Basin, Wyoming.Emended diagnosis: Differs from other species of Foxomomys in

having a smaller and wider P4 relative to length. Further differsfrom F. fremdi in lacking a diastema between C1 and P2. Furtherdiffers from F. vossae in having P4 and a uniformly sloping

Figure 5. Micro-CT scan images of Foxomomys captured using Avizo 6: F. fremdi, UA 21015, L maxilla P2eM3 in buccal (A) and occlusal (B) views. F. fremdi, UA 21011, R dentary C1, P3eM3 (reversed) in buccal (C), lingual (D), and occlusal (E) views. F. vossae, UA 9151, L P4 in buccal (F), lingual (G), and occlusal (H) views. F. gunnelli, UM 77528, L dentary P4, in buccal(I), lingual (J), and occlusal (K) views. Scale bar ¼ 1 mm.

S.G.B. Chester, J.I. Bloch / Journal of Human Evolution 65 (2013) 109e142114

mesiodorsal margin in buccal view and one (rather than threepoorly defined) talonid cusp(s).

Micromomys Szalay, 1973Type species: M. silvercouleei Szalay, 1973Diagnosis: As for the type species.M. silvercouleei Szalay, 1973 (Figs. 4AeC, 6)Holotype: YPM-PU 17676, R partial dentary P4 and M2, and

alveoli for I1, C1, P2, P3, M1, M3.Known distribution: Late Paleocene of North America (late Tif-

fanian (Ti-5a), Princeton Quarry, northern Bighorn Basin,Wyoming).

Emended diagnosis: Differs from all other micromomyids inhaving P4 with mesiodistally short trigonid that is relatively tallerthan the talonid. Further differs from Chalicomomys and Dry-omomys in having a dentary with the mesial mental foramen belowthe single-rooted P2 (rather than below mesial root of P3). Furtherdiffers from Dryomomys in having less enlarged P4 relative to M2,relatively larger M2 paraconid, and mediolaterally narrowermandibular corpus. Further differs from Foxomomys in havingsingle-rooted P2, wider P4 relative to length with a cristid obliquathat does not climb the postvallid, and rounder cusps on M2 with

protoconid and metacone subequal in height. Further differs fromTinimomys in retaining P2, less bunodont molar cusps, and a den-tary that is more uniform in depth.

Discussion: M. silvercouleeiwas the first species of micromomyiddescribed. This species was and still is only represented by theholotype, a dentary preserving two broken teeth (P4 and M2). P4morphology appears uniquely derived, however, the broken anddistorted nature of the teeth makes it somewhat difficult to assesswhether there are any synapomorphies uniting M. silvercouleei withany other species of micromomyid. An interpretation of the original,undistorted morphology of these teeth has been illustrated (Szalay,1973; Szalay and Delson, 1979), but no attempts have been made tophysically prepare these teeth in fear that the holotype would befurther damaged. In order to gain confidence about the truemorphology of these teeth, the holotype was micro-CT scanned, andthe teeth were digitally disassembled along breaks and recon-structed using Avizo 6 software (Fig. 6). Results suggest that certainnatural breaks are filled with matrix, making P4 appear taller than itactually was. However, M. silvercouleei can still be diagnosed fromall other micromomyids in having P4 with a mesiodistally shorttrigonid that is relatively taller than the talonid. Micro-CT scans also

Figure 6. Micro-CT scan images of the holotype and only known specimen of Micromomys silvercouleei, YPM-PU 17676, R dentary P4, M2, captured using Avizo 6: P4 was digitallyseparated into three parts along natural breaks (A), and reconstructed (B, distal; C, lingual; D, buccal; E, occlusal views) providing a more accurate view of P4 morphology than thecurrent condition of the specimen (F, distal; G, lingual, H, buccal; I, occlusal views). YPM-PU 17676 in buccal (J) view. M2 was also digitally separated into three parts along naturalbreaks (K) and reconstructed (L, buccal, M, lingual; N, occlusal views) providing a more accurate view of M2 morphology than the current condition of the specimen (O, buccal, P,lingual; Q, occlusal views). All digital reconstructions were created using Avizo 6 software. Scale bar ¼ 1 mm.

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allowed us to confidently assess the lower dental formulaof M. silvercouleei, which is 1.1.3.3, with a single-rooted P2 (seeFig. 4AeC).

Chalicomomys Beard and Houde, 1989Type species: C. antelucanus Beard and Houde, 1989Diagnosis: As for the type species.C. antelucanus Beard and Houde, 1989 (Figs. 4DeF, 7, 8)Holotype: USNM 425589, L partial dentary P3 (broken), P4eM2,

and alveoli for I1, C1, P2, and M3.Referred specimens: UCM locality 84126: UCM 54585, R partial

dentary P4eM1, alveoli for M2 (Fig. 8DeF); UM locality SC-123:UM 76682, L partial dentary M2e3 (Fig. 8AeC); UM locality SC-4:USNM 512221, L dentary M1e2, and alveoli for I1, C1, P2e4, and M3(Fig. 7KeM); USNM 512241, R M2 (Fig. 7I,J); USNM 512258, R P4

(Fig. 7E,F); USNM 512261, R partial maxilla M1 and alveoli for M2

(Fig. 7G,H); USNM 516587, L partial maxilla P2eM3 (Fig. 7C,D).

Locality and horizon: UCM 54585 was collected at Urruty’sCrossing (UCM locality 84126) in the Wasatch Formation, PowderRiver Basin, Wyoming (see Robinson, 1994). UM 76682 wascollected at UM SC-123 in the Clarks Fork Basin, Wyoming (seeGunnell, 1989). All USNM specimens were recovered from earlyEocene faunal zone Wa-1, Willwood Formation, Clarks Fork Basin,Park County, Wyoming. These specimens were etched from afreshwater limestone block that was collected near UM fossil lo-cality SC-4 (see Beard and Houde, 1989 and references therein).

Known distribution: Early Eocene of North America (Wasatch-ian (Wa-1) of the Bighorn Basin, Wyoming, and earlyWasatchian ofthe Powder River Basin, Wyoming).

Emended diagnosis: Differs from all micromomyids other thanFoxomomys in having a relatively more transversely elongate M2

comparedwithM1. Differs from Foxomomys in having single-rooted P2,wider P4 relative to length, protoconid and metaconid subequal in

Figure 7. Micro-CT scan images of new specimens of Chalicomomys antelucanus (CeM) and the only previously known maxillary specimen (AeB) captured using Avizo 6: USNM425588, R maxilla P3e4, M2e3, in buccal (A) and occlusal (B) views. USNM 516587, L maxilla P2eM3, in buccal (C) and occlusal (D) views. USNM 512258, R P4, in buccal (E) andocclusal (F) views. USNM 512241, R M2, in buccal (I) and occlusal (J) views. USNM 512261, R maxilla M1, in buccal (G) and occlusal (H) views. USNM 512221, L dentary M1e2, in buccal(K), lingual (L), and occlusal (M) views. Scale bar ¼ 1 mm.

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Table 1Summary of dental measurements (in millimeters) for Chalicomomys antelucanusfrom SC-4.

Tooth N OR x SD CV

P3L 1 0.91 e e e

P3W e e e e e

P4L 3 1.29e1.35 1.33 0.03 2.42P4W 3 0.90e0.91 0.91 0.01 0.64P4H 3 0.94e1.08 0.99 0.08 7.89M1L 2 1.01e1.07 1.04 0.04 4.08M1W 2 0.78e0.79 0.79 0.01 0.90M2L 3 0.98e1.06 1.01 0.04 4.11M2W 2 0.81e0.83 0.82 0.01 1.72M3L e e e e e

M3W e e e e e

MD 2 1.75e1.95 1.85 0.14 7.64P2L 1 0.80 e e e

P2W 1 0.47 e e e

P3L 2 1.13e1.15 1.14 0.01 1.24P3W 2 0.96e1.00 0.98 0.03 2.89P4L 3 1.20e1.30 1.25 0.05 4.04P4W 3 1.34e1.54 1.47 0.12 7.84M1L 2 0.95e0.98 0.97 0.02 2.20M1W 2 1.47e1.59 1.53 0.08 5.55M2L 3 0.93e0.97 0.96 0.02 2.41M2W 3 1.40e1.60 1.52 0.11 6.96M3L 2 0.79e0.88 0.84 0.06 7.62M3W 2 1.55e1.58 1.57 0.02 1.36

L, length; W, width; H, height; MD, mandibular depth below distal root of P4; N,sample size; OR, observed range; x, mean; SD, standard deviation; CV, coefficient ofvariation.

Figure 8. Micro-CT scan images of Chalicomomys antelucanus captured using Avizo 6: UM 76682, L dentary M2e3, in buccal (A) lingual (B), and occlusal (C) views, and UCM 54585, Rdentary P4eM1, in buccal (D) lingual (E), and occlusal (F) views. Scale bar ¼ 1 mm.

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height on lowermolars, relatively larger P3 comparedwithM1, and lesspronounced ectoflexus and parastyle on upper molars. Further differsfrom F. fremdi in lacking diastemata between I1 and C1, and C1 and P2.Further differs from Micromomys in having a less tall P4 relative tolength with a mesiodistally longer trigonid relative to width, and amesial mental foramen under mesial root of P3 (rather than under P2).Further differs from Dryomomys in having relatively smaller P3e4compared with lower molars, mediolaterally narrower mandibularcorpus, relatively smaller P2e4 compared with upper molars, and P3

with smaller protocone situated on less inflated protocone lobe.Further differs from Tinimomys in retaining P2, having a P4 with asmaller talonid, lacking lingually continuous cingula with periconesand hypocones on P4eM2, having a less developed P3 protocone lobe,having more pronounced ectoflexus on upper molars, and having adentary that is fairly uniform in depth.

Description and comparison: Detailed descriptions of previouslyknown tooth positions of C. antelucanus were published by Beardand Houde (1989). Here, based on five new specimens from thetype locality, we describe new tooth positions (P2, M1) and docu-ment variation in previously described tooth positions. A summaryof dental measurements of C. antelucanus specimens from UM SC-4can be found in Table 1.

The upper dentition of C. antelucanus was previously knownonly from USNM 425588 (Fig. 7A,B), a right partial maxilla with P3e4, M2e3 (Beard and Houde, 1989). USNM 516587, a left partialmaxilla with P2eM3 (Fig. 7C,D), is the most complete maxillaryspecimen of C. antelucanus known to date. USNM 516587 is brokendirectly mesial to P2, so the presence of a diastema between P2 andthe tooth mesial to it (presumably C1) cannot be evaluated. P2 isbuccolingually compressed and double-rooted like all othermicromomyids for which this tooth position is known. The crown isdominated by a paracone with a postparacrista that descends fromthe apex of the paracone and becomes less distinct near the base of

a small metastylar cusp. A smaller, yet distinct parastylar cuspule ispresent on the mesial portion of the crown and a faint lingualcingulum is present on the distal end of the tooth. The P2 ofC. antelucanus is very similar to that of Tinimomys tribos (seeChester and Beard, 2012). T. graybulliensis (see Gunnell, 1989; Rose

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et al., 1993), D. millennius (see Secord, 2008), and D. szalayi (seeFig. 3), differ from C. antelucanus and T. tribos in lacking a distinctparastylar cusp. D. millennius and D. szalayi further differ in beingrelatively larger and more bulbous (especially D. szalayi, which alsohas a more pronounced lingual cingulum that extends to the mesialaspect of the tooth). The only published P2 of F. fremdi (UA 21015;Fox, 1984) is too incomplete for comparisons, although a newcomplete specimen has been reported (Scott, 2008).

The P3 and P4s of C. antelucanus reported here are very similar tothose of the only previously known specimen (USNM 425588;Fig. 7A,B). The parastylar and metastylar regions of P3 are slightlymore expanded in USNM 516587 (Fig. 7C,D), although not to thedegree of that of Dryomomys dulcifer, D. millennius, or D. szalayi.Similarly, the protocone lobe of P3 of USNM 516587, although worn,is not quite as narrow as it appears in the only previously knownspecimen. The P4s of USNM 516587 and 512258 (Fig. 7E,F) areextremely similar to the previously known specimen. USNM516587 also has a median crest between the pre- and post-protocristae that connects to the lingual base of the paracone, butdiffers from the other known specimens in having a secondmediancrest that connects the postprotocrista to themidpoint between thelingual base of the paracone and metacone. This forms two sets of‘wings’ that resemble the cristae of themolar conules, which occursin other micromomyids and appears to be variable.

The M1 of C. antelucanus was not previously known, and thistooth position is described here based on two specimens (USNM516587, Fig. 7C,D; USNM 512261, Fig. 7G,H). M1 is smaller than P4,and slightly longer and narrower (buccolingually) thanM2, giving ita less transverse appearance. The paracone is slightly larger thanthe metacone, and the postparacrista and premetacrista are posi-tioned in a mesiodistally-oriented line between these cusps. Thepreparacrista and postmetacrista curve mesiobuccally and dis-tobuccally, respectively, to join a continuous ectocingulum. Theectoflexus of M1 is not as pronounced as that of M2 in Chalicom-omys, which is common in micromomyids. The M1 ectoflexus is notas pronounced as that of F. fremdi, but is similar to that of T. tribos inbeing more pronounced than that of T. graybulliensis or D. szalayi,which suggests that Chalicomomys is primitive in this regard. Aparastyle is present and is about the same size as that of M2, but notas pronounced as that of M3 in Chalicomomys. The paraconule andmetaconule are small, and have respective cristae. The conules areconnected to the protocone by the pre- and postprotocristae, whichoutline the trigon basin. The area of the trigon basin increases fromM1 to M3. The protocone is larger, yet approximately the height ofthe other two trigon cusps, and it is oriented mesiobuccally. Pre-and postcingula are present, but they do not connect to form alingual cingulum as in Tinimomys. No hypocone or periconeis present. Although there appears to be a break in slope wherea postprotocingulum would be present, this structure is notdistinct.

The two new M2s of C. antelucanus reported here (USNM516587, Fig. 7C,D; USNM 512241, Fig. 7I,J) are very similar to the M2

described by Beard and Houde (1989). The diminutive cuspulebuccal to metacone on the ectocingulum that was documented onthe M2 of USNM 425588 (Beard and Houde, 1989) is not as distinctin these specimens, although the stylar region is similarly quitedeveloped with a pronounced ectoflexus. Overall, M2 ofC. antelucanus is quite similar to that of D. dulcifer (Chester andBeard, 2012). The new specimen of M3 (USNM 516587) is verysimilar to the previously described specimen, although it differsslightly in having a more pronounced metacone and metaconule.

A new dentary of C. antelucanus (USNM 512221, Fig. 7KeM)preserves the first and second molars and the mesial alveoli betterthan any previously known specimen. This specimen confirms theinterpretation of Beard and Houde (1989) that C. antelucanus had a

dental formula of 1.1.3.3 (with a single-rooted I1, C1, and P2, anddouble-rooted teeth distal to P2), and lacks diastemata between I1and C1 and between C1 and P2. The P2 alveolus is larger than that ofthe holotype. Other than an extremely worn and partially brokenM2 (USNM 425587), the crowns of M1 and M2 of C. antelucanuswere previously only known from the holotype. USNM 512221 hasM1 and M2 that are generally similar to those of the holotype,although the paraconid is slightly more lingually located on M2.

Discussion: Nine specimens referred to C. antelucanus have beenrecovered from the type locality SC-4. A left dentary withM2e3 (UM76682; Fig. 8AeC) from a different Wa-1 locality in the Clarks ForkBasin, SC-123, was originally attributed to ‘Micromomys’ will-woodensis (Gunnell, 1989), and was later referred to C. antelucanuswhen Chalicomomys was first described (Beard and Houde, 1989).Beard and Houde (1989) referred UM 76682 to C. antelucanusbecause its size, molar morphology (unknown for D. willwoodensis),and provenance (Wa-1) may be in better agreement withC. antelucanus. These authors suggested that lower molars with ametaconid and protoconid of subequal height was diagnostic ofC. antelucanus, but this condition can also be found inM. silvercouleei, as well as D. szalayi, D. dulcifer, and D. millennius.Referral of UM 76682 is complicated by the fact that it only pre-serves M2, which is not particularly diagnostic, andM3, which is nototherwise known for C. antelucanus. Therefore, the best comparisonis that of mandibular depth. The depth of the dentary below thedistal alveolus of M2 in UM 76682 is 2.07 mm, whereas it is2.56 mm in the holotype of D. willwoodensis and 2.42 mm inD. szalayi. The samemeasurement was taken for three specimens ofC. antelucanus (USNM 425586, 1.96 mm; USNM 425587, 1.87 mm;USNM 512221, 1.91 mm), which are all more similar to that of UM76682 than to D. willwoodensis. This suggests that UM 76682 be-longs to C. antelucanus, and represents the only M3 known for thisspecies. The M3 is similar to that of Dryomomys in having a hypo-conulid that is more developed than that of F. fremdi, yet not asexpanded and broad as in Tinimomys.

A partial dentary with P4eM1 (UCM 54585; Fig. 8DeF) from theearly Wasatchian of the Powder River Basin was attributed toD. willwoodensis (Robinson, 1994). The absolute size of P4, as well asthe depth and mediolateral width of the dentary, is smaller thanthat of D. willwoodensis and more similar in size to that ofC. antelucanus. Lower molars are not known for D. willwoodensis,although the size of the alveoli suggests that the relative size of P4to M1 is quite large as in D. szalayi. It should also be noted that theM1 paraconid in UCM 54585 is somewhat reduced, which is acondition similar to that found in some species of Dryomomys.Overall, the relative size of P4 toM1 and absolute size of the dentaryin UCM 54585 appears to be most similar to that of C. antelucanusand it is tentatively assigned to this species.

Validity of the genus Chalicomomys: Beard and Houde (1989)suggested that Chalicomomys is useful as a separate genusbecause it serves as a morphologic intermediate betweenMicromomys sensu lato (i.e., Foxomomys and M. silvercouleei) andTinimomys. Rose and Bown (1996) claimed that characters origi-nally used by Beard and Houde (1989) to distinguish ChalicomomysfromMicromomys do not validate generic separation. Secord (2008)also considered Chalicomomys a junior synonym of Micromomysand demonstrated that the original diagnosis of Chalicomomyssuffers from using the most plesiomorphic and best-known speciesof ‘Micromomys,’ F. fremdi, instead of the type species,M. silvercouleei, for all comparisons. Our current understanding ofthe relationship between C. antelucanus and M. silvercouleei iscomplicated by the fragmentary nature of the only known spec-imen of M. silvercouleei. There are clear differences between thetwo taxa and similarities are best interpreted as plesiomorphic.Also, there is a three million year difference in age between

Figure 9. Micro-CT scan images of Dryomomys P3e4 captured using Avizo 6. D. mil-lennius, UM 110140, L P3e4 cropped from L maxilla P2eM1, in occlusal (A) view. D.dulcifer, CM 71796, L P3 (cast), and CM 72149, L P4 (cast), in occlusal (B) view. D. szalayi,UM 41870, R P3e4 (reversed) cropped from palate in occlusal (C) view. Dryomomys sp.,UM 39849, R P4 (reversed) in buccal (D) and occlusal (E) views. Scale bar ¼ 1 mm.

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M. silvercouleei and C. antelucanuswith no known intermediates. Assuch, we suggest that recognizing the genus Chalicomomys as ajunior synonym of Micromomys is unneccesary especially given thearbitrary nature of ranks above the species level.

Dryomomys Bloch et al., 2007Type species: D. szalayi Bloch et al., 2007Included species: D. szalayi (Bloch et al., 2007), D. willwoodensis

(Rose and Bown, 1982), D. millennius (Secord, 2008), D. dulcifer(Chester and Beard, 2012).

Known distribution: Late Paleocene to early Eocene of NorthAmerica (Tiffanian (Ti-5b) to early Wasatchian (Wa-2) of the Big-horn Basin, Wyoming, and middle Clarkforkian (Cf-2) of Big MultiQuarry, Washakie Basin, Wyoming).

Emended diagnosis: Differs from all other micromomyids inhaving large and inflated P2e4 and P3e4 relative to molars, and amandibular condyle that is higher relative to the toothrow. Furtherdiffers from all other micromomyids except T. graybulliensis inhaving lingually expanded P3 with strong protocone and smalldistolingual basin bounded by the preprotocrista and post-protocingulum. Further differs from Foxomomys andM. silvercouleeiin having a mesial mental foramen under the mesial root of P3.Further differs from Foxomomys and Chalicomomys in having ataller P4 relative to length and similarly sized M1 and M2 (ratherthan a relatively more transversely elongate M2 compared withM1). Further differs from Foxomomys in having single-rooted P2,and a longer and broader M3 hypoconulid (although not to theextent as that of Tinimomys). Further differs from Tinimomys inhaving a P2, having a taller P4 relative to length, and lackinglingually continuous cingula with no distinct pericone or hypoconeon P4eM2. Further differs from T. graybulliensis in having slightlynarrower I1 with less developed mediocone and no lateroconule,and in lacking P3 metacone.

Discussion: Two species previously allocated to other micro-momyid genera are attributed to Dryomomys here. ‘Micromomys’willwoodensis and ‘M.’ millennius are referred to Dryomomys pri-marily based on the relatively large size of their known premolartooth positions.D. willwoodensiswas first attributed toMicromomyswhen micromomyids were poorly known (Rose and Bown, 1982).D. willwoodensis was then referred to Chalicomomys because its P4was viewed as more similar to that of C. antelucanus than to P4s ofknown species of Micromomys, and like C. antelucanus, it was alsoonly known from the early Eocene (Beard and Houde, 1989). Asrecognized by Rose and Bown (1982), the P4 of D. willwoodensiswasconsiderably larger than that of any other micromomyid known.The only P4 of similar size that has been described since is that ofD. szalayi (Bloch et al., 2007).

D. millennius was attributed to Micromomys by Secord (2008),but shares many premolar characteristics that were originallyconsidered autapomorphies of D. szalayi by Bloch et al. (2007).Although it is possible that more than one lineage of micro-momyids independently evolved relatively large premolars, aDryomomys clade is supported in the phylogenetic analysis pre-sented below. The seemingly progressive increase in premolar sizefrom the late Tiffanian D. millennius to D. dulcifer to D. szalayi toD. willwoodensis in the early Wasatchian may well illustrate theevolution of premolar specializations in this group of micro-momyids (Figs. 9 and 10).

The premolar specializations of Dryomomys are similar to thoseof certain early fossil euprimates, especially those of omomyids.The relatively pronounced lingual expansion of P3e4 found inD. szalayi is similar to that of omomyids such as Absarokius abotti.D. szalayi is also similar to some omomyids such as Uintaniusameghini in having relatively large upper and lower premolars (seeSzalay, 1976; Szalay and Delson, 1979). Though similarities of pre-molar specializations between Dryomomys and these omomyids

are clearly convergent, this observation may indicate that thesesmall early euarchontans were eating and or processing compara-ble food in similar ways.

D. szalayi Bloch et al. 2007 (Figs. 3, 9C, 10GeI, 11e15GeI)Holotype: UM 41870, partial cranium with L and R I1eM3 (R C1

absent), L dentary I1eM3 (M2 absent), R dentary I1eM3, and partialpostcranial skeleton.

Known distribution: Late Clarkforkian (Cf-3), UM locality SC-327, lower Willwood Formation, Clarks Fork Basin, Wyoming.

Emended diagnosis: Differs from all other species of Dryomomysin having relatively larger P2e4 compared with upper molars, widerP3 relative to length with larger protocone, more pronouncedprotocone lobe, and larger distolingual basin, and P4 that is widercompared with themolars with a more lingually dipping protoconelobe. Also differs from all species of Dryomomys in having a nar-rower P3 relative to length with more developed talonid basin, M1that lacks a distinct paraconid, and M2 with relatively small para-conid. Further differs from D. millennius in having larger P4 relativeto size of lower molars, M1e2 with more centrally situated para-conids, and P4 with the apex of the protocone more closely situatedto that of the paracone and metacone. Further differs fromD. willwoodensis in having P4 with broader talonid basin and moreventrally distended distobuccal lobe.

Description: There are clearly two single-rooted incisors in thepremaxillae of D. szalayi (Fig. 11). Distal to that, the mesial-mosttooth in the maxilla is double-rooted, followed by P2e4 and M1e3

(Fig. 12). We interpret the mesial-most tooth in the maxilla as a

Figure 10. Micro-CT scan images of Dryomomys lower teeth captured using Avizo 6: D. millennius, UM 109659, R dentary P3eM2, in buccal (A), lingual (B), and occlusal (C) views.D. dulcifer, CM 71657, R P3 (cast), and CM 69990, L P4 (cast, reversed), in buccal (D), lingual (E), and occlusal (F) views. D. szalayi UM 41870, cropped portion of R dentary I1eM3

illustrating P2eM3 in buccal (G), lingual (H), and occlusal (I) views. D. willwoodensis, YPM-PU 17732, L dentary P4 (reversed), in buccal (J), lingual (K), and occlusal (L) views. Scalebar ¼ 1 mm.

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canine, with P1 absent and suggest that the upper dental formula ofD. szalayi is 2.1.3.3.

The crowns of I1e2 (Fig. 11) are complete in the right and leftpremaxillae. The crown of I1 is vaguely ‘mitten-shaped’ (although,in lateral perspective, it appears ‘hook-shaped’) with a subdivisionof the distal end into a strong anterocone and a weak mediocone,the latter almost completely defined by a shallow furrow sepa-rating the two cusps, and the presence of a short internal crestrunning proximally from its apex. The ‘thumb’ of the mitten-shaped crown has a single, small (but distinct) cusp. The crown ofI2 is shorter than that of I1, laterally compressed, and slightlyrecurved at its apex. It has a single cusp (anterocone) at its apex,with a weak medial crest, but no mediocone. There is a swelling atthe base of the tooth, although there are no cusps present.

The crown of C1 (Fig. 12) is broken, missing most of the distalhalf of the crown. It is smaller than P2, double-rooted, longer thanwide with a mesially situated apical cusp, and lacks a lingualcingulum. There is a swelling at the base of the crown, giving theimpression that it may have been similar in that respect to themorphology of P2. The mesial root is considerably smaller indiameter than the distal root.

P2 (Fig. 12) has two roots and is separated from C1 by a shortdiastema. The crown is longer than wide with a mesially situatedapical cusp and a strong lingual cingulum that extends to anincipiently basined distal heel. In comparable morphology, themesial bulge is generally similar to that of the canine.

The P3 (Fig. 12) has three roots. In occlusal view, the crown of P3

is generally triangular in outline, with the buccal margin of thecrown slightly convex, and the mesio- and distolingual marginsstrongly concave at the midline. The crown of P3 is dominated by alarge cusp (paracone) that is situated on the central part of thebuccal margin. P3 has a strong postparacrista, but lacks any evi-dence of a metacone. The postparacrista descends in a straight linedistally from the apex of the paracone to the distal margin of thecrown, where it swings sharply around the distobuccal corner ofthe crown and continues mesially along the buccal margin as acingulum for about one-third of the length. The mesial face of the

paracone is mostly smooth, although a faint trace of a preparacristadescends from the apex of the paracone mesially for a very shortdistance. Though there is no obvious parastyle, a strong cingulum ispresent on the mesiobuccal corner of the tooth that extendslingually to join the protocone. The crown of P3 is linguallyexpanded with a strong protocone and a small distolingual basinbounded by the preprotocrista and postprotocingulum.

The P4 (Fig. 12) has three roots, is semimolariform, is distinctlylonger buccally than lingually, and is concave at the midline, at thelevel of the protocone, on the mesial and distal margins of thecrown (much more so on the mesial margin). The crown of P4 is thewidest in the toothrow. The buccal aspect of the crown of P4 isnearly equal in length to that of P3, and considerably longer thanthat of M1. The crown of P4 has three well-developed buccal cusps.The paracone is the largest cusp and is situated slightly distal to thecenter of the buccal side of the tooth. The metacone is more wornbut clearly smaller than the paracone, and is connate with theparacone for most of its height. A shallow valley separates theparacone and metacone buccally and lingually. The parastyle islocated on a large, mesially-projecting parastylar lobe on the buccalend of the tooth. The parastyle would very likely have been adistinct cusp, perhaps even larger than the metacone, although thisobservation is mostly by inference as much of the mesial portion ofthe parastylar lobe is stronglyworn. The parastyle is separated fromthe paracone by awell-developed deep valley that is defined by twocrests: the first descends the parastyle lingually and is joined to theprotocone by a strong preprotocrista, and the second descends theworn parastyle buccally to join the mesial portion of an ectocing-ulum before it is interrupted by the base of the paracone. A straightline can be drawn from a faint preparacrista across to a shortpostparacrista that likely connects to the closely appressed meta-cone by a very short premetacrista, although this is difficult to seedue to wear especially on the metacone. The postmetacrista curvesdistobuccally to connect with the distal ectocingulum, which is alsointerrupted by the base of the paracone. The protocone is situatedvery close to the paracone andmetacone, and is lingual and slightlydistal to the paracone, resulting in a very small trigon basin. The

Figure 11. Dryomomys szalayi (holotype: UM 41870) L premaxilla I1e2 in buccal(A), lingual (B), and occlusal (C) views.

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postprotocrista extends posterobuccally to about half the distancebetween the protocone and metacone, at which point it dips downaround the distal margin of the crown to the interstitial facet be-tween P4 and M1. While no distinct metaconule is present, a small

crest extends to the base of the paracone from this point formingpart of the margin of the trigon basin, similar to the morphology ofa premetaconule crista. Likewise, a small median crest, similar tothe morphology of a postparaconule crista (although no paraconuleis present), extends from the preprotocrista to the base of theparacone and forms part of the margin of the trigon basin. Thepreprotocrista extends from the protocone to a crest connected tothe parastyle. A large lingually sloping protocone lobe extends fromthe apex of the protocone to the lingual margin of the crown. Thelobe is narrow and oval shaped, lacking a flat lingual margin. Well-developed pre- and postcingula are present, but not linguallycontinuous. Both cingula climb from the base of the protocone,with the precingulum ending part way up and the postcingulumextending all the way to the apex. These crests form two incipientbasins, or ‘furrows’ (Secord, 2008) with the mesial longer andshallower than the distal one.

The upper molars of D. szalayi are generally similar to those ofother micromomyids (Fig. 12). The lingual half of the M1 crown isnarrower than the buccal half and shifted slightly distally relative tothe midline. The M1 trigon cusps are all fairly similar in height andsize. The largest cusp is the protocone, which faces mesially. Thesecond largest cusp is the paracone and the smallest trigon cusp isthe metacone. Like that of P4, the metacone is the most worn cuspon M1. The parastyle is weakly developed. Like that of P4, the pre-and postparacristae and premetacrista are worn but appear to forma straight line across the tooth mesiodistally. The postmetacristacurves distobuccally and connects with the ectocingulum. Theectocingulum is buccally continuous, and the ectoflexus is not welldeveloped. The paraconule, metaconule, and respective cristae arewell developed, although are short with the conules closelyappressed to the paracone and metacone. The pre- and post-protocristae connect the protocone to conules and surround amoderately expanded trigon basin. Pre- and postcingula are welldefined, but not lingually continuous, instead they briefly climb theprotocone before terminating. There is no obvious development ofa pericone or hypocone.

The crown of M2 of D. szalayi is very similar to that of M1 in sizeand morphology (Fig. 12). M2 differs from M1 in being slightlynarrower mesiodistally on the buccal side, resulting in a morequadrate tooth. The ectocingulum on M2 is slightly interrupted bythe buccal base of the paracone, and the ectoflexus is more pro-nounced than that of M1. There is less development of a hypoconeswelling on M2 relative to that of M1.

The M3 of D. szalayi has a relatively smaller metacone with nopostmetacrista and a relatively larger parastyle than M1 and M2

(Fig. 12). The ectocingulum is interrupted by the paracone andforms a minor buccal extension where a mesostyle would belocated.

We interpret the lower dental formula of D. szalayi to be 1.1.3.3(see discussion on tooth homology above). The crown of I1 is mostlypreserved on the left side (the tip is missing) and completely pre-served on the right side (Figs. 13 and 14). The crown of I1 is pro-cumbent, long, highly compressed mediolaterally, and culminatesin a sharp, tapering tip. A thin but distinct dorsal crest (margoc-ristid; Gingerich, 1976) extends from the tip to the base of thecrown, with no margoconid present. A second crest runs from thelingual aspect of the tip lower on the lingual surface of the crown,and then swings up to nearly join the margocristid at the base ofthe crown. The two crests define a very shallow lingual surfacewitha slight bulge running down its midline marking the break in slopebetween the dorsal and lingual surfaces of the crown.

The single-rooted C1 of D. szalayi is positioned directly distal toI1, with a very small diastema separating the two alveoli (Figs. 13and 14). The crown of C1 is elongate and projects mesially awayfrom the root, covering the diastema, to the base of I1. The crown

Figure 12. Dryomomys szalayi (holotype: UM 41870) R maxilla P2eM3 in buccal (A) and occlusal (B) views. L maxilla C1eM3 in buccal (C) and occlusal (D) views.

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has a large mesially placed protoconid followed by a low bulboustalonid heel.

The single-rooted P2 of D. szalayi is positioned directly distal toC1, also with a very small diastema separating the two alveoli(Figs. 13 and 14). Themorphology of P2 is generally similar to that ofthe C1 in being elongate and projectingmesially away from the root.It differs from the C1 in being smaller and having a shorter (abouttwo-thirds the length) mesial projection (protoconid) that does notcover the entire mesial diastema. It also has a low talonid heel, butwith a more distinctly developed cusp than that of C1.

The P3 of D. szalayi is double-rooted and the crown is abouttwice the size of P2 (Figs. 13 and 14). The crown of P3 is oval inocclusal view and is approximately twice as long as it is wide. Thetrigonid is mesially inflated, lacks a paraconid, is dominated by aprotoconid, and a faint crest (paracristid or preprotocristid) de-scends from the apex of the protoconid mesially before curvinglingually toward the base. The crown of P3 has a wide, short talonidheel with a shallow basin and no clearly defined cusps.

The crown of P4 is considerably larger and taller than any otherin the toothrow distal to I1 (Figs. 13 and 14). The shape of P4 is ovalin occlusal view, with the mesial portion of the tooth somewhatnarrower than the distal portion of the tooth. The crown of P4 isfairly exodaenodont with the base moderately distended dis-tobuccally. The trigonid is wide, formed by a tall protoconid, andthere is no paraconid or metaconid present. A paracristid descendsthe protoconid mesially for about one-third of the length of thetrigonid, then turnsmesiolingually and continues downmost of theheight of the crown nearly vertically before terminating about atthe level of the talonid. In buccal view, there is a break of slopealong the mesiodorsal margin at the point along the paracristidwhere it curves lingually. Also at this point, another smaller crestsplits off the paracristid and descends mesially merging with thefaint crest on the mesiobuccal margin of the trigonid. The para-cristid defines the mesial margin of a distinct mesiolingual exca-vation that is distally bounded by a rib descending from the apex ofthe protoconid. A second, slightly smaller lingual excavation is alsopresent distal to the apex and underlying rib of the protoconid. Thepostvallid face is almost transverse across the crown. The cristidobliqua and postcristid areworn, but it seems as though two poorlydefined cusps were present, separated by a shallow valley. Thehypoconid appears to have been larger and more distinct than theentoconid. The talonid basin is small and wider than long. Thecristid obliqua is angled slightly lingually and connects to thepostvallid slightly lingual to the midline of the wall. The hypoflexidis deep and occupies the buccal half of the talonid.

The crown of M1 of D. szalayi is square in outline and generallysimilar to that of some other micromomyids in being low-crownedwith fairly bulbous cusps (Figs. 13 and 14). The trigonid is abouttwice the height of the talonid with a distinct protoconid andmetaconid. The protoconid and metaconid are of similar size withthe metaconid only slightly larger, and the two cusps are closelyappressed, separated by a small but distinct valley. A small para-conid is present on themidline of the trigonid, directlymesial to thevalley. The paraconid is situated on a very short paracristid thatconnects to the base of the protoconid. In occlusal view the cusp islophate, whereas in lingual view it is cuspate (but very small). Avery faint precingulid is present on the mesiobuccal wall of thetrigonid. The talonid has a fairly deep basin, surrounded on all sidesby crests. Two main cusps dominate the talonid, the entoconid anda somewhat larger hypoconid located at the distolingual and dis-tobuccal extremes of the basin respectively. The cristid obliqua is astraight crest that extends mesiolingually from the hypoconid tothe base of the postvallid where it ends below the protoconidwithout extending up the face of the postvallid. A poorly-defined,lophate hypoconulid is located lingual to the midline of the tooth,

slightly closer to the entoconid than the hypoconid. A faint post-cingulid is present on the distal aspect of the talonid between thehypoconulid and the hypoconid that is not continuous with theprecingulid (i.e., no evidence of an ectocingulid).

The crown of M2 of D. szalayi is similar to that of M1 in beingsquare in outline (although slightly shorter and wider), with low-crowned and fairly bulbous cusps (Fig. 13). The trigonid of M2 isnot as tall as that of M1, about 1.5 times the height of the talonidwith a distinct protoconid, metaconid, and paraconid. As for M1, theprotoconid and metaconid are of similar size with the metaconidslightly larger. The two cusps are less closely appressed in M2 thanfor M1, separated by a larger and distinct valley. A moderately sizedparaconid, larger than that of M1, is present on the midline of thetrigonid of M2, directly mesial to the valley but closer to the othertrigonid cusps than that of M1. The paraconid is situated on a shortparacristid that connects to the protoconid. In occlusal and lingualviews, the paraconid is cuspate and projects somewhat mesially inM2, rather than lophate as in M1. A faint but slightly more pro-nounced precingulid is present on M2 on the buccal wall of thetrigonid. As for M1 the talonid has a fairly deep basin, surroundedon all sides by crests. Two main cusps, the entoconid and a some-what larger hypoconid located at the distolingual and distobuccalextremes of the basin, respectively, dominate the talonid. Thetalonid basin of M2 is slightly wider than that of M1, with theentoconid and hypoconid morewidely spaced. As for M1, the cristidobliqua of M2 is a straight crest that extends mesiolingually fromthe hypoconid to the base of the postvallid where it ends below theprotoconid without extending up the face of the postvallid. Unlikethat of M1, a faint swelling in the position of a mesoconid is presenton the cristid obliqua of M2 just before it meets the postvallid. As inM1, a poorly defined, lophate hypoconulid is located lingual to themidline of M2, slightly closer to the entoconid than the hypoconid.Also like M1, a faint postcingulid is present on the distal aspect ofthe talonid between the hypoconulid and the hypoconid of M2 thatis not continuous with the precingulid (i.e., no evidence of anectocingulid).

The crown of M3 of D. szalayi is similar to that of other micro-momyids for which it is known in being elongate in outline, withlow-crowned and fairly bulbous cusps (Figs. 13 and 14). The trig-onid of M3 is similar to that of M2 in being about 1.5 times theheight of themesial aspect of the talonid with a distinct protoconid,metaconid, and paraconid. The protoconid and metaconid on theM3 are of similar size with the protoconid slightly larger, unlike thatof M1e2 inwhich the metaconid is slightly larger. The two cusps areless closely appressed in M3 than for M1 (similar to that of M2), andare separated by a larger and distinct valley. A distinct paraconid,larger than that of M1e2, is present slightly lingual to the midline ofthe trigonid of M3, mesial to the valley but closer to the othertrigonid cusps than that of M1 (similar to that of M2). The paraconidof M3 is connected to the protoconid by a somewhat longer para-cristid than that of M1e2. In occlusal and lingual views, the para-conid is cuspate and projects somewhat mesially in M3 (similar tothat of M2), rather than reduced and lophate as in M1. A morepronounced precingulid is present on the buccal wall of the trig-onid of M3 than that of the other lower molars. The talonid of M3has a fairly deep, elongate basin that is dominated by a distallyexpanded hypoconulid. The pronounced hypoconulid extendsdorsally almost to the height of the trigonid. The entoconid and alarger hypoconid are located at the lingual and buccal extremes ofthe M3 talonid basin, respectively. The talonid basin of M3 is similarin width to that of M1, with the entoconid and hypoconid similarlyspaced. The entoconid of M3 is shifted more distally relative to thehypoconid than that of M2, and to a greater extent M1 in which thecusps are nearly level with each other. As for M1e2, the cristidobliqua of M3 is a straight crest that extends mesiolingually from

Figure 13. Dryomomys szalayi (holotype: UM 41870) R dentary I1eM3 in lingual (A), buccal (B), and occlusal (C) views.

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the hypoconid to the base of the postvallid where it ends below theprotoconid without extending up the face of the postvallid with nodevelopment of a mesoconid (which is present on M2 but not M1).Also like the other lower molars, a faint postcingulid is present onthe distal aspect of the talonid between the hypoconulid and thehypoconid of M3 that is not continuous with the precingulid (i.e., noevidence of an ectocingulid across the face of the protoconid).

The dentary is fairly uniform in depth from P4eM3, with twodistinct mental foramina below the mesial roots of P4 and P3,respectively (Figs. 13 and 14). A short, unfused mandibular sym-physis quickly divides into two distal extensions. The dorsal portionextends to the C1 root and the ventral portion as far as the root of P2.The coronoid process is tall and vertically oriented. The mandibularcondyle is situated high on the ascending ramus, well above theheight of the cheek teeth. The articular surface of the condyle issmoothly convex, wide, and hemicylindrical. The angular process isrelatively elongate and pointed, with a flat dorsal surface and slightmedial inflection.

Comparison and discussion: The I1 of D. szalayi is similar to thatof T. graybulliensis in general shape and proportions, although it issomewhat narrower (Fig. 15). It differs in having a less developedmediocone, mostly defined by an internal crest, giving D. szalayi anarrower distal end than that of T. graybulliensis. It further differsfrom that of T. graybulliensis in having only a single cusp at its base.Following the description and terminology of Rose et al. (1993), thiscusp may be the homolog of the lateroconule in the I1 of

T. graybulliensis, with the posterocone completely absent, althoughthis cusp has previously been considered to be the posterocone(Bloch et al., 2007; Chester and Beard, 2012). Recently, isolated uppercentral incisors of micromomyids were described from Big MultiQuarry, Washakie Basin, Wyoming (the type locality of T. tribos andD. dulcifer; Chester and Beard, 2012). These I1s have a faint medi-ocone and no lateroconule, making them more similar to that ofD. szalayi than to that of T. graybulliensis. This seems to suggest thatthey should be attributed to D. dulcifer. However, the dentition ofT. tribos appears to be more plesiomorphic than T. graybulliensis inseveral ways, and T. tribos is more abundant than D. dulcifer at BigMulti Quarry, so it is also possible that these isolated plesiomorphicI1s could belong to T. tribos (Chester and Beard, 2012).

Rose et al. (1993) suggested that while micromomyids weregenerally similar to plesiadapids, carpolestids, saxonellids, andparomomyids in having multicusped upper incisors, the relativelysimple I1 of T. graybulliensis was most similar among plesiadapi-forms to isolated incisors from Gidley Quarry that were tentativelyassigned to Palaechthon alticuspis. This could suggest a close rela-tionship among micromomyids and palaechthonids, or that thisrelatively simple I1 morphology is plesiomorphic for plesiadapi-forms (Rose et al., 1993). Bloch et al. (2002) described the deciduousdentition of the paromomyid plesiadapiform, Acidomomys hebeti-cus, including a dI1 that was quite similar to the isolated incisorsfrom Gidley Quarry. Given the similarity, Bloch et al. (2002) sug-gested that these isolated upper incisors belong to the paromomyid

Figure 14. Dryomomys szalayi (holotype: UM 41870) L dentary I1eM3 (M2 absent) in lingual (A), buccal (B), and occlusal (C) views.

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Paromomys despressidens (not to P. alticuspis), which is also knownfrom Gidley Quarry. These authors also suggested that such simpleI1 morphology may have been present in the ancestor that gave riseto all later plesiadapiforms, however, they noted that the I1 of theoldest and possibly most primitive plesiadapiform, Purgatorius, wasstill unknown (Bloch et al., 2002).

Two years later, an isolated right I1 was attributed to P. janisaefrom the earliest Paleocene of Montana (Clemens, 2004). Thistooth is similar to that of D. szalayi in having only a poorlydeveloped mediocone and narrower distal crown. The I1 ofP. janisae differs from that of D. szalayi, however, in having a smallposterocone in addition to the lateroconule, making it moresimilar in this respect to T. graybulliensis. The relatively simplemorphology of I1 documented in D. szalayi has also been docu-mented in primitive members of other plesiadapiform groups,such as Pandemonium dis (Van Valen, 1994) and Chronolestes simul(Beard andWang, 1995). Additionally, an isolated incisiform tooth(likely I1) recently attributed to the palaechthonid Torrejoniawilsoni lacks complex multicusped morphology (Silcox andWilliamson, 2012). These observations suggest that this simpleincisor morphology is primitive and that multicusped upper in-cisors evolved more than once among plesiadapiforms (Beard andWang, 1995; Bloch et al., 2007). The fact that the simple I1

morphology of Dryomomys is so similar to that of other primitive

plesiadapiforms such as Chronolestes suggests that more complexincisors evolved within Micromomyidae, from a more simpletooth like that of D. szalayi to a more complex tooth like that ofT. graybulliensis. It is also possible that the simple morphology ofthe I1 of D. szalayi is more plesiomorphic than that of the I1 thatwas attributed to P. janisae.

The I2 of D. szalayi differs from that of T. graybulliensis (Roseet al., 1993) in having a less well-developed medial crest, againmaking the crown narrower at the distal end (Fig. 15). LikeT. graybulliensis, the I2 of D. szalayi is generally similar to that ofother plesiadapiforms, such as the paromomyid Ignacius and theplesiadapid Nannodectes, in being simple and compressed laterally(Rose et al., 1993).

It appears that the C1 of T. graybulliensis (only known fromalveoli; Rose et al., 1993) would have been similar to that ofD. szalayi in crown size and proportions of roots. D. millennius alsohad a similarly sized, double-rooted C1 (only known from alveoli;Secord, 2008). The diastema between C1eP2 is relatively shorter inT. graybulliensis than that of D. millennius and D. szalayi. Manyplesiadapiforms have a single-rooted C1 and several derivedmembers of various families (e.g., Carpolestidae and Plesiadapidae)have lost this tooth completely (Silcox, 2001). All micromomyidshave a double-rooted C1, as in many microsyopids, and the paro-momyid Phenacolemur jepseni (Simpson, 1955). The presence of a

Figure 15. Micro-CT scan images of upper incisors of micromomyids Tinimomys graybulliensis and Dryomomys szalayi captured using Avizo 6. Wasatchian T. graybulliensis, USNM461201, palate with L I1e2, R P2eM3, in lingual (A), buccal (B), and occlusal (C) views. New Clarkforkian T. graybulliensis, UM 39927, L premaxilla I1e2, in lingual (D), buccal (E), andocclusal (F) views. Dryomomys szalayi, UM 41870, R premaxilla I1e2 (reversed), in buccal (G), lingual (H), and occlusal (I) views. Scale bar ¼ 1 mm.

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double-rooted C1 in these fossil taxa and in extant P. lowii anddermopterans suggests that this condition was present in theancestral euarchontan.

The crown of P2 of D. szalayi is distinctly different from that ofT. graybulliensis (Gunnell, 1989; Rose et al., 1993) in having astronger lingual cingulum that extends onto a distal, almostbasined, heel (in the area of the metastylar cusp of F. fremdi,although most of the P2 is not preserved in that specimen).D. millennius has a moderate cingulum on P2, although it is not asstrong as that of D. szalayi. In general, the crown of P2 is somewhatlarger relative to M1 in D. szalayi compared with that ofD. millennius, and substantially larger than that of T. graybulliensisand F. fremdi.

D. szalayi differs from all other micromomyids in having a largerP3 relative to the size of its upper molars. D. dulcifer andD. millennius most closely approximate this condition (Fig. 9), andF. fremdi is least similar due to its extremely small P3. The P3 ofD. szalayi has more pronounced parastylar, metastylar, and proto-cone lobes than any other micromomyid, giving the tooth a moreinflated look, although D. dulcifer, D. millennius, and T. graybulliensisapproach this condition. The P3 of C. antelucanus and F. fremdi lackthe development of these lobes, although C. antelucanus is uniquein possessing a distinct parastyle (Beard and Houde, 1989), andF. fremdi is unique in possessing a metastyle. The P3 of D. szalayi issimilar to that of all other micromomyids for which this tooth isknown in lacking a metacone, with the exception of

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T. graybulliensis, which has a variably developed metacone. The P3

of D. szalayi possesses a distinct protocone with a moderatelydeveloped basin, which is most similar to that of D. dulcifer andD. millennius compared with all other micromomyid species.

The P4 of D. szalayi is larger and more lingually sloping relativeto M1 than that of any other micromomyid. Though the positionand relative size of the buccal cusps of D. szalayi are generallysimilar to othermicromomyids for which P4 is known, they differ insome critical ways. The position of the metacone and the orienta-tion of the metacrista in D. szalayi is similar to nearly that of allother micromomyids for which P4 is known, with the metaconelocated directly distal to the paracone before the postmetacristacurves distobuccally. In contrast, the P4 metacone of F. fremdi islocated more distobuccally on a more gradually curving metacristaforming a blade-like structure, similar to that of Purgatorius (e.g.,Lillegraven et al., 1979; Fox and Scott, 2011) and the presumedprimitive condition. The parastylar lobe of D. szalayi is similar tothat of Tinimomys in being larger and more transversely extendedthan other micromomyids. The valley separating the parastyle fromthe paracone is more pronounced in D. szalayi than in any otherknown micromomyid, although most closely approximating thecondition of D. dulcifer and D. millennius (Fig. 9). The mesial anddistal aspects of the ectocingulum in D. szalayi are similar to thoseof D. dulcifer and T. graybulliensis in being more developed thanthose ofD. millennius, F. fremdi, and C. antelucanus. The P4 protoconeof D. szalayi is most similar among micromomyids to that ofD. dulcifer and D. millennius, and to a lesser extreme C. antelucanus,in being situated very close to the paracone and metacone andhaving a transversely extended protocone lobe. In this way, it isdistinctly different from F. fremdi, which has a more lingually sit-uated protocone and transversely shorter lobe. Comparison withthat of Tinimomys is complicated by the fact that the protocone isusually worn, and by the presence of a hypocone, which is absent inD. szalayi. However, although the protocone lobe of Tinimomys isfairly large, the protocone cusp is more lingually positioned with alarger trigon basin than that of D. szalayi. As for all other micro-momyids except Tinimomys, the P4 pre- and postcingula ofD. szalayi are not lingually continuous. D. szalayi is also similar toother micromomyids in having a rounded lingual margin of theprotocone lobe, in contrast to the squared-off condition inT. graybulliensis.

The crowns of M1e3 of D. szalayi are similar to those ofT. graybulliensis in having a shallow ectoflexus and parastyle. Incontrast, the ectoflexus and parastyle are more pronounced inF. fremdi and to a lesser extent C. antelucanus and T. tribos. D. szalayidiffers from F. fremdi and is more similar to other micromomyids inhaving less transverse molars with similar buccal and linguallengths, resulting in more quadrate teeth. The relative molar size ofD. szalayi is close to that of T. graybulliensis and T. tribos in havingsimilarly sized M1 and M2, whereas M2 is considerably more elon-gate than M1 in F. fremdi and C. antelucanus (no other species ofmicromomyid preserves both tooth positions). The upper molars ofT. graybulliensis and T. tribos are distinctly different from all othermicromomyids, including D. szalayi, in having a continuous lingualcingulumwith awell-developedhypocone andpericone (exceptM3,which lacks a hypocone and pericone in all known micromomyidtaxa). The condition in D. szalayi, in which the upper molars havewell-developed pre- and postcingula (with only incipient develop-ment of cuspules in M1e2) but lack a lingually continuous cingulum,ismost similar to that of theM2 ofD. dulcifer andM1 ofD. millennius.In contrast, C. antelucanus, and to a greater extent F. fremdi, have lesswell-developed pre- and postcingula with no development of cus-pules on the upper molars. The M2 of D. szalayi is similar to othermicromomyids in lacking the variably expressed cuspule buccal tothe metacone that has been documented in that of C. antelucanus

(Beard and Houde, 1989). The M1 of D. szalayi is similar to that ofother micromomyids in having a rounded lingual margin with astronger postcingulum than precingulum. In contrast, the M1 ofD. millennius is more squared-off with a flatter lingual margin.

The crown of I1 in D. szalayi is very similar to that ofT. graybulliensis. It differs in that the I1 crown of T. graybulliensis hasa dorsoventrally deeper base and a more expanded dorsal surface,forming a small dorsal shelf running for most of its length. The I1morphology of micromomyids is most similar among plesiadapi-forms to that of Saxonella (Rose et al., 1993), Phenacolemur, andPicromomys (Silcox, 2001; Silcox et al., 2002), although other ple-siadapiform taxa that have an elongate I1 and lack amargoconid arealso broadly similar (e.g., Carpolestes; Bloch and Gingerich, 1998),contrasting with the lanceolate form of other plesiadapiforms (e.g.,microsyopids).

D. szalayi is the third micromomyid (see also T. graybulliensis andF. fremdi) for which the crown of C1 is known, although a singlealveolus present in several other species (M. silvercouleei, F. vossae,F. gunnelli, C. antelucanus) indicates that this tooth is consistentlysingle-rootedwithinMicromomyidae. F. fremdi is distinct inhaving alonger and more mesially extended C1 than that of T. graybulliensisand D. szalayi to a lesser extreme. Though the crown of C1 is some-what longer inD. szalayi than that of T. graybulliensis, theyare similarin having a more horizontally oriented crown, as opposed to that ofF. fremdi, which is oriented at almost 45 degrees to the toothrow. Thecrown of C1 inD. szalayi has a lowbulbous talonid heel that lacks thedistinct talonid cusppresenton thatof T. graybulliensisand toa lesserextreme F. fremdi. The C1 of D. szalayi is similar to that ofT. graybulliensis, M. silvercouleei, C. antelucanus, and F. gunnelli inhaving a shorter diastema between I1 and C1 than that of F. fremdi.

Other than D. szalayi, the only micromomyid for which thecrown of P2 has been recovered is F. fremdi (Fox,1984). The crown ofP2 in D. szalayi is smaller than that of F. fremdi relative to lowermolars, and more mesially projecting. As such, the morphology ofthe crown of P2 in D. szalayi is very similar to that of its canine,whereas the P2 crown morphology in F. fremdi is more similar tothat of its own P3. The P2 of D. szalayi is similar to that ofM. silvercouleei and C. antelucanus in being single-rooted (based onalveoli; see Fig. 4). In contrast F. fremdi, F. gunnelli (based on alveoli),and probably F. vossae (based on alveoli) had double-rooted P2 andT. graybulliensis has lost P2 entirely.

The P3 of D. szalayi is most similar to that of D. dulcifer andD. millennius among micromomyids in being larger and highercrowned relative to the lowermolars. The P3 ofD. szalayi has amoremesially extended trigonid than that of F. fremdi, perhaps mostsimilar to the condition in D. millennius (the protoconid is broken inthe only specimen for which P3 is preserved; Fig. 10), although itdiffers from that of T. graybulliensis in lacking a cusp mesial to theprotoconid. Though comparison to C. antelucanus is difficult as theonly known specimen for which the P3 is preserved is heavilydamaged, with the entire buccal side missing (Beard and Houde,1989), it seems that this tooth would also have been mesiallyextended,withno clear evidence of amesial cusp. The P3 ofD. szalayidiffers from that of T. graybulliensis and especially D. dulcifer andD. millennius in being narrower and less inflated, more like that ofF. fremdi. It also has a slightly more developed talonid basin than allothermicromomyids forwhich P3 is known, although itmost closelyresembles D. dulcifer and D. millennius in this respect.

The P4 of D. szalayi is larger relative to the lower molars thanthat of all other micromomyids except possibly D. willwoodensis(Fig. 10; this specimen only preserves the crown of P4 and molaralveoli). Much of this size difference is due to the wider and moreinflated trigonid of D. szalayi, which is most similar to that ofD. dulcifer, D. willwoodensis, and D. millennius in this regard, andthat of C. antelucanus and T. graybulliensis to a lesser extent. The

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mesial aspect of the trigonid of D. szalayi is similar to that ofD. millennius in that it does not narrow as muchmesially as in othermicromomyids. The distobuccal aspect of the trigonid of D. szalayiis similar to that of D. dulcifer and M. silvercouleei, and to a lesserextent F. vossae, F. fremdi, and F. gunnelli, in being less extendedbuccally than that of D. willwoodensis, D. millennius, C. antelucanus,and T. graybulliensis. However, this feature is variable and influ-enced by the breadth of the mesial aspect of the trigonid and thenature of the hypoflexid. For example, D. szalayi differs fromD. willwoodensis in having the floor of the hypoflexid extend to thebuccal margin of the tooth, giving the impression that it has a lesspronouced distobuccal lobe despite the fact that it is still quitewide. As for all other micromomyids, except T. graybulliensis, whichhas a variably present, small paraconid (Szalay, 1974; Bown andRose, 1976), there is no development of a paraconid on the P4 ofD. szalayi. The P4 of D. szalayi is similar to that of D. dulcifer andC. antelucanus in being moderately exodaenodont with its basemore distended distobuccally than that of D. willwoodensis and lessdistended than that of T. graybulliensis and Tiffanianmicromomyidssuch asD. millennius. The P4 paracristid ofD. szalayi is similar to thatof D. dulcifer, D. millennius, and C. antelucanus in that it is not asdistinct and does not extend as far down to the base of the tooth asit does in D. willwoodensis, but is more distinct than other micro-momyids. As for all other micromomyids except F. fremdi andF. gunnelli, when oriented in buccal view, the P4 paracristid ofD. szalayi has a break in slope along the mesiodorsal margin whereit curves lingually. However, like D. dulcifer, D. szalayi differs fromthe remaining species in having a shorter mesiodorsal margin witha shallow slope before the paracristid curves lingually, superficiallyalmost approaching the condition of that of F. fremdi and F. gunnelliin which the mesial margin appears smoothly convex with nodistinct break in slope. The cristid obliqua of D. szalayi is similar tothat of D. dulcifer, D. millennius, D. willwoodensis, C. antelucanus,M. silvercouleei, and T. graybulliensis in not climbing the postvallidand differs from that of F. fremdi, F. vossae, and F. gunnelli in which itclimbs the postvallid for a short distance. The P4 talonid of D. szalayiis shorter than wide, and shorter relative to the length of the tooth,than that of any other micromomyid. The talonid basin is small likethat of all othermicromomyids other than T. graybulliensis. The P4 ofD. szalayi has two talonid cusps, a hypoconid and an entoconid,similar to that of D. dulcifer, D. millennius, M. silvercouleei,T. graybulliensis, C. antelucanus, and F. fremdi (although presence ofentoconid is variable; Fox, 1984). F. gunnelli differs from D. szalayi inonly having a poorly defined hypoconid on the talonid of P4, andF. vossae and possibly D. willwoodensis differ in having three faint P4talonid cusps. As for all other known micromomyids, the P4 talonidcusps of D. szalayi are not as pronounced as those ofT. graybulliensis.

The crowns of M1e2 of D. szalayi are similar to those of all othermicromomyids in being generally square in outline and being low-crowned with fairly bulbous cusps (Fig. 10). More specifically, likeother micromomyids, the lower molar cusps of D. szalayi are not asbulbous as those of T. graybulliensis, nor are they as high-crowned asthose of F. fremdi. The relative height of the trigonid to talonid inM1e

2 (twice theheight inM1and slightly less inM2) inD. szalayi is similarfor all micromomyids for which these tooth positions are known. Asin other micromomyids, D. szalayi has a M1 with a distinct proto-conid andmetaconid closely appressed, yet separated by a small butdistinct valley, and a M2 with a wider valley making the protoconidandmetaconid less closely appressed. However, the crowns of M1e2

in D. szalayi differ from those of other micromomyids in having aslightly larger metaconid than protoconid. In contrast, the proto-conid is considerably larger than the metaconid in that of F. fremdi,and somewhat larger in D. dulcifer, D. millennius, M. silvercouleei(only known molar is M2), T. graybulliensis, and C. antelucanus,

although this difference is considerably stronger inM1 thanM2. Thecrowns ofM1e2 ofD. szalayi are similar to all othermicromomyids inthat the paraconid is the smallest trigonid cusp. However, the M1 ofD. szalayi differs from that of all other micromomyids in having aconsiderably more reduced paraconid that forms a small loph on avery shortparacristid in occlusal view. TheM1paraconid is alsomorecentrally located, directly mesial to the valley separating the meta-conid and protoconid, than that of other micromomyids includingC. antelucanus. In contrast, the paraconid of M1 is larger, morecuspate, connects to a longer paracristid, and is more lingually sit-uated (mesial to the metaconid) in F. fremdi, F. vossae, D. millennius,and T. graybulliensis. TheM1 paraconid ofD. dulcifer is similar to thatof D. szalayi in being centrally located, however, it is much moredistinct (Chester and Beard, 2012). The paraconid of M2 in D. szalayiis also more reduced than that of other micromomyids, but less sothan that of M1. The paraconid of M2 in D. szalayi is similar to that ofD. dulcifer and C. antelucanus in the central location of this cusprelative to the midline, but differs from that of F. fremdi,M. silvercouleei, D. millennius, and T. graybulliensis inwhich the cuspismore lingually positioned. Though the crowns ofM1e3 ofD. szalayiare similar to all other micromomyids in lacking a well-definedectocingulid, they differ somewhat in having less defined pre- andpostcingula on the mesio- and distobuccal margins. The talonidmorphology of M1e2 of D. szalayi is generally similar to that of allother micromomyids. Prior to the discovery of the holotype ofD. szalayi (UM 41870), M3 was only unambiguously known forT. graybulliensis and F. fremdi. In these taxa the talonid of M3 ismarkedly different, with the hypoconulid considerably expandedand distally projecting in T. graybulliensis, whereas the hypoconulidof F. fremdi is large and extended distally, but is more cuspate. Thehypoconulid ofM3 inD. szalayi is somewhat intermediate in that it issimilar to that of T. graybulliensis in being expanded, but it is nar-rower and tapers distally like that of F. fremdi. More recently, M3 hasbeen recovered for T. tribos andD. dulcifer (Chester and Beard, 2012),and the morphology of these teeth is most similar to that ofT. graybulliensisandD. szalayi, respectively. TheM3ofD. szalayi is alsoquite similar overall to the M3 attributed to C. antelucanus above,especially in the slight expansion of the hypoconulid, but it differs inhaving a shorter trigonid relative toM3 length,with amore centrallysituated paraconid (UM 76682; Fig. 8AeC).

As for most other micromomyids, the dentary of D. szalayi ismore uniform in depth than that of T. graybulliensis and T. tribos inwhich the mandibular depth increases distally from the tip of themandibular symphysis, with its greatest depth below P4 (Beard andHoude, 1989; Chester and Beard, 2012). The position of the mentalforamina are below the mesial roots of P3 and P4, respectively, andis similar in this way to the condition in D. millennius,C. antelucanus, and Tinimomys, but differs from that of F. fremdi andF. gunnelli in which the mesial-most alveolus is farther forward,under the distal root of P2, and from that ofM. silvercouleei inwhichit is under a single-rooted P2. The presumed primitive condition isillustrated by that of Purgatorius in which the mental foramina arebeneath and slightly mesial to the mesial roots of P2 and P4. Theback of the dentary of D. szalayi is very similar to that of othermicromomyids for which it is known, although the condyle appearsto be higher relative to the toothrow than that of T. graybulliensisand C. antelucanus, in which it is about the same height as P4. Thismay be related to a relatively more herbivorous diet in D. szalayithan these other taxa (see Rose, 1975), although this conclusionremains to be tested with more rigorous quantitative analyses ofmorphology. The articular surface of the condyle of D. szalayi issimilar to that of T. graybulliensis and C. antelucanus in beingsmoothly convex and hemicylindrical, but is clearly relatively widermediolaterally than for either of those taxa. The angular process ofD. szalayi is similar to that of T. graybulliensis, and contrasts with the

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condition in C. antelucanus (a simple pointed structure) in having adorsally oriented concavity with a slight medial inflection, thoughtto be related to the insertion of the medial pterygoid muscle (Beardand Houde, 1989). The short, unfused symphysis of D. szalayi issimilar in morphology to that of T. graybulliensis (Figs. 13 and 14).

D. willwoodensis (Rose and Bown, 1982) (new combination)(Fig. 10JeL)

Holotype: YPM-PU 17732, L partial dentary P4 and alveoli forM1e2.

Known distribution: EarlyWasatchian (Wa-2), UM locality SC-2,Willwood Formation, Bighorn Basin, Wyoming.

Emended diagnosis: Differs from all other species of Dryomomysin having P4 with more distinct paracristid that extends fartherdown toward the base of the crown, narrower talonid basin relativeto length with three poorly defined talonid cusps (rather than twomore defined cusps), less ventrally distended distobuccal lobe, andan invagination at the base of the hypoflexid at the distobuccalmargin of the crown. Further differs fromD. dulcifer andD. szalayi inhaving a wider P4 relative to length. Further differs fromD. millennius in having relatively larger P4.

Discussion: D. willwoodensis is the only species of Dryomomysknown from the early Eocene (Wa-2). Rose and Bown (1982) notedthat the molars of D. willwoodensis were approximately the samesize as those of other micromomyids (based on alveoli; the crownswere not recovered), yet P4 was approximately 25% larger than thatof M. silvercouleei and M. vossae. This observation appears to becorrect and such a relatively large P4 is one of the characteristicsunique to Dryomomys. However, before other species ofDryomomyswere described, D. willwoodensis was referred to Chalicomomysbecause C. antelucanus is also known from the early Eocene (Wa-1)and is somewhat similar in P4 morphology (Beard and Houde,1989). Although no other species of Dryomomys are known fromthe earliest Eocene, and it is possible that P4 size may haveincreased convergently in more than one group of micromomyids,the size and morphology of P4 (and mandibular depth) ofD. willwoodensis is most similar to those of Dryomomys species suchas D. szalayi. The phylogenetic analysis presented below supportsthe placement of D. willwoodensis in a Dryomomys clade.

D. millennius (Secord, 2008) (new combination) (Figs. 9A,10AeC)

Holotype: UM 109659, R partial dentary P3eM2 and partialalveolus for I1.

Knowndistribution: Late Tiffanian (Ti-5b), Y2K Quarry, northernBighorn Basin, Wyoming.

Emended diagnosis: Differs from all other species of Dryomomysin having a wider P4 relative to length and a smaller P4 relative tolower molars, with more ventrally distended distobuccal lobe andmore distinct distobuccal cingulum. Further differs from D. szalayiand D. dulcifer in having smaller and less inflated P3 with smallerprotocone, and smaller P4 relative to upper molars with a lesslingually expanded protocone lobe. Further differs fromD. szalayi inhaving a wider P3 relative to length, M1e2 with more cuspate andmore lingually situated paraconids, and more pronounced dis-tobuccal cingula, and M1 with more squared-off lingual margin.

Discussion: Secord (2008) tentatively attributed UM 110140, amaxilla with P2eM1 and alveoli for C1, to ‘M.’ millennius, althoughhe noted that it could also belong toM. silvercouleei. This specimenwas collected at Y2K Quarry, which lies 85 m above PrincetonQuarry where the only known specimen of M. silvercouleei wasdiscovered. The P4 of D. millennius is considerably wider than thatof M. silvercouleei, and the P3 and P4 of D. millennius are quite widelike the P3 and P4 of UM 110140 (Secord, 2008). These character-istics are consistent with the generally wide upper premolarsknown for D. dulcifer and D. szalayi, and support the attribution ofUM 110140 to D. millennius.

D. dulcifer Chester and Beard, 2012 (Figs. 9B, 10D-F)Holotype: CM 72292, L partial dentary M1e3.Known distribution: Middle Clarkforkian (Cf-2), Big Multi

Quarry, Washakie Basin, Wyoming.Emended diagnosis: Differs from all other species of Dryomomys

in having a narrower P4 relative to length. Differs from D. szalayi inhaving relatively longer and narrower P3e4, smaller P3 relative toknown upper molar tooth positions, P3 with less pronouncedprotocone lobe and smaller protocone, M2 with more pronouncedectoflexus and shorter lingual margin, wider P3 relative to length,andM1with distinct paraconid. Further differs fromD. millennius inhaving relatively larger, more inflated P3, and P4 with morelingually expanded protocone lobe and apex of protocone moreclosely situated to that of paracone and metacone.

Discussion: Chester and Beard (2012) suggested that Plesiadapiscookei might have occurred earlier at Big Multi Quarry in theWashakie Basin than at Cf-2 localities in the Bighorn Basin.Regardless, Big Multi Quarry is Cf-2 by definition (P. cookei rangezone; Gingerich, 2003) based on the presence of P. cookei andabsence of Copecion (56.2e56.5 Ma (millions of years ago); Secordet al., 2006).

Dryomomys sp. (Fig. 9D,E)Referred specimen: UM 39849, R P4 (broken).Locality and horizon: Middle Clarkforkian (Cf-2) SC-19, Bighorn

Basin, Wyoming.Description and comparison: The isolated P4 is broken with the

entiremesial margin and parastylar lobemissing. Nevertheless, thistooth preserves much of the crown and is noticeably smaller(1.65mmwidth) than that of D. szalayi and D. dulcifer. It differs fromthat of Tinimomys in lacking a lingually continuous cingulum andhypocone, and differs from Chalicomomys in having a more elon-gate protocone lobe and a relatively smaller metacone with a lesswell-defined postmetacrista. UM 39849 has an elongate protoconelobe with pronounced mesial and distal furrows most similar tothat of D. szalayi, D. dulcifer, and D. millennius. Although the pro-tocone lobe may be somewhat more elongate than that ofD. millennius, this P4 is similar to that of D. millennius in having aprotocone that is not as closely appressed to the paracone andmetacone as it is in D. szalayi and D. dulcifer.

Discussion: UM 39849 differs from the P4s of D. dulcifer andD. szalayi in being smaller and having a protocone that is morelingually situated on the crown. This morphology is similar to thatof D. millennius, F. fremdi, and C. antelucanus, and is likely plesio-morphic. Although this specimen may represent morphologicalvariability in P4 of D. szalayi, it appears most similar to that ofD. millennius overall. Given the isolated and incomplete nature ofthe specimen, it is only attributed to the genus Dryomomys here.

Tinimomys Szalay, 1974Type species: T. graybulliensis (Szalay, 1974)Included species: T. graybulliensis (Szalay, 1974), T. tribos

(Chester and Beard, 2012).Known distribution: Late Paleocene to early Eocene of North

America (early Clarkforkian (Cf-1) to early Wasatchian (Wa-2) ofthe Bighorn Basin, Wyoming; middle Clarkforkian (Cf-2) of BigMulti Quarry, Washakie Basin, Wyoming; and early Wasatchian ofthe Powder River Basin, Wyoming).

Emended diagnosis: Differs from all other micromomyids inhaving pre- and postcingula strongly confluent lingually on P4eM3

with variably developed hypocone and pericone on P4eM2. Furtherdiffers from all other micromomyids in lacking P2, having large P4talonid basin with pronounced cusps, relatively low-crowned mo-lars with more bulbous cusps, M3 with a more expanded hypo-conulid, and dentary that reaches its greatest depth below P4.

Discussion: The diagnosis for the genus Tinimomys has beenemended to include the recently described species, T. tribos (Chester

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and Beard, 2012). T. tribos retains several plesiomorphic dental fea-tures that have been further modified in T. graybulliensis. Tinimomyscan be further differentiated from other micromomyids in having aP4 paraconid, although this feature is variably expressed.

T. graybulliensis Szalay, 1974 (Figs. 15AeF, 16e18)Holotype: YPM-PU 17899, L partial maxilla P4eM2.Referred specimens: UCM locality 84117 (early Wasatchian):

UCM 62749, R partial dentary P4eM3 (Fig. 17EeG). UCM locality89079 (early Wasatchian): UCM 76918, L partial maxilla P3e4

(Fig.17A,B); UCM 76919, R partial dentary I1, M1. UCM locality 91056(early Wasatchian): UCM 65916, R partial dentary I1, P4. UCM lo-cality 98074 (earlyWasatchian): UCM 86800, R partial dentary M1e

2. UCM locality 2004086 (early Wasatchian): UCM 101486, L partialmaxilla P4eM3 (Fig. 17C,D). UCM locality 2010009 (earlyWasatchian): UCM 62762, R partial dentary P4eM3 (Fig. 18A,B);UCM 70619, L partial dentary M3 (Fig. 17HeK).

UM locality SC-179 (Cf-1): UM 36199, R M2 (Fig. 16AeD). UMlocality SC-117 (Cf-2): UM 39877, R M2; UM 39878, R partial den-tary M3, alveoli for M2; UM 39879, R M3; UM 39880, R M1; UM39881, L partial maxilla M2; UM 39883, L partial dentary I1eM1, M3(C1 broken) (Fig. 16EeG), alveoli for M2; UM 39927, L partial pre-maxilla I1e2 (Fig. 15DeF); UM 39928, R M2; UM 39929, L I1; UM39931, L partial dentary M3 (M3 broken); UM 39932, R partialdentary M2; UM 39933, R partial dentary P3eM3, I1 (I1 broken)(Fig. 16HeJ). UM locality SC-62 (Cf-2): UM 82683, R partial dentaryI1, P3eM1, alveoli for C1, M2e3. UM locality SC-4 (Wa-1): USNM512211, L partial maxilla P4eM3 (P4, M3 broken); USNM 512212, Rpartial maxilla P3eM1, alveoli for M2e3; USNM 512213, R partialmaxilla P3eM2, alveoli for P2, M3; USNM 512214, R partial maxillaP4eM2 (M1 broken); USNM 512215, R partial maxilla M1e2, alveolifor M3; USNM 512216, L partial maxilla M1e3; USNM 512217, Lpartial maxilla M2e3; USNM 512218, L partial maxilla M1e2; USNM512219, L partial dentary P4eM1, alveoli for M2e3; USNM 512220, Lpartial dentary P3eM2, alveoli for C1, M3; USNM 512225, L partialdentary P3e4, R partial dentary P3e4 (broken), L partial maxilla P2eM2 (P2 broken); USNM 512231, R partial dentary P4eM1, alveoli for

Figure 16. Micro-CT scan images of new specimens of Tinimomys graybulliensis from the Clarbuccal (A), occlusal (B), lingual oblique (C), and lingual (D) views. UM 39883, L dentary I1eMbuccal (H), lingual (I), and occlusal (J) views. Scale bar ¼ 1 mm.

M2e3; USNM 512232, R partial maxilla P3eM2, alveoli for P2, M3;USNM 512233, L partial maxilla P2eM2, alveoli for M3; USNM512234, L partial maxilla M1 (M1 broken), alveoli for M2; USNM512235, R partial maxilla M1e2, alveoli for M3; USNM 512236, Lpartial maxilla P4eM1, alveoli for M2; USNM 512237, L partialmaxilla P2e4 (P4 broken), alveoli for C1; USNM 512238, R partialdentary P4eM1, alveoli M2e3; USNM 512242, L partial dentary M3;USNM 512248, R P4; USNM 512249, L P4 (broken); USNM 512251, RP4; USNM 512252, R M3; USNM 512253, R M1 or M2 (broken);USNM 512254, L M3; USNM 512255, R M3; USNM 512256, L M3

(broken); USNM 512257, L M3; USNM 512259, R M1 (fragment);USNM 512260, L M1; USNM 512263, R M2; USNM 512266, L M3;USNM 512267, L M3; USNM 512268, R M1; USNM 512269, R M1;USNM 512271, L M3; USNM 512273, R P4; USNM 512274, R M3;USNM 512275, L M3; USNM 512277, R M1; USNM 512280, L P4;USNM 512281, L M3; USNM 512282, L M3; USNM 512283, L M2;USNM 512285 L M2, USNM 512681 L P3; L M2 (broken); USNM512682, R P3; USNM 512692, R maxilla P3, alveoli for C1eP2; USNM512772, L M2 (broken); USNM 512778, R I1; USNM 512786, L M3;USNM 512804, L P4; USNM 516544, L dentary M3.

Locality and horizon: UCM specimens were collected from theearly Wasatchian (Wa-1 or Wa-2) of the Wasatch Formation,Powder River Basin, Wyoming. UM and USNM specimens wererecovered from freshwater limestones from the late Paleocene (Cf-1, Cf-2) of the Fort Union and (Cf-2, Cf-3)Willwood Formations, andearly Eocene (Wa-1, Wa-2) of theWillwood Formation in the ClarksFork Basin, Wyoming. All USNM specimens reported here wererecovered from a freshwater limestone block that was collectednear the early Eocene (Wa-1) UM fossil locality SC-4 (see Beard andHoude, 1989 and references therein).

Emended diagnosis: Differs from T. tribos in being slightly largerin most tooth dimensions, lacking diastema between P2 and P3,having P3 with metacone (although variably expressed) with moreenlarged protocone lobe, having P4 parastyle that is positionedhigher relative to the protocone resulting in a shorter preparacrista,and having more bulbous molar cusps.

kforkian of the Clarks Fork Basin, Wyoming, captured using Avizo 6. UM 36199, R M2, in1, M3, in buccal (E), lingual (F), and occlusal (G) views. UM 39933, R dentary P3eM3 in

Figure 17. Micro-CT scan images of new specimens of Tinimomys graybulliensis from the Wasatchian of the Powder River Basin, Wyoming, captured using Avizo 6. UCM 76918, Lmaxilla P3e4, in buccal (A) and occlusal (B) views. UCM 101486, L maxilla P4eM3, in buccal (C) and occlusal (D) views. UCM 62749, R dentary I1, P4eM3, in buccal (E), lingual (F), andocclusal (G) views. UCM 70619, L dentary M3, in buccal (H), occlusal (I), oblique (J), and lingual (K) views. Scale bar ¼ 1 mm.

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Description and comparison: Fourteen late Paleocene speci-mens of T. graybulliensis previously recovered from Clarkforkianlimestones (Bloch, 2001) are reported here. Most of these speci-mens are isolated molars, although several nearly complete den-taries and upper incisors are also preserved. These teeth are quitesimilar to previously known specimens of T. graybulliensis, as are

the 54 new specimens of T. graybulliensis from the earlyWasatchianthat are also reported here.

I1 and I2 of T. graybulliensis were previously only known fromone specimen, USNM 461201 (Fig. 15A-C), from the earlyWasatchian (Rose et al., 1993). A partial premaxilla with I1 and I2

(UM 39927; Fig. 15D-F) and an isolated I1 (UM 39929) of

Figure 18. Micro-CT scan images of a new specimen of Tinimomys graybulliensis (AeB)and specimens previously attributed to Myrmekomomys loomisi (CeF) from theWasatchian of the Powder River Basin, Wyoming, captured using Avizo 6. UCM 62762,R dentary P4eM3, in buccal (A) and occlusal (B) views. UCM 48544, R dentary M1e3, inbuccal (C) view, and M3 cropped in occlusal (D) view. UCM 52038, R dentary M1e2, inbuccal (E) and occlusal (F) views. Scale bar ¼ 1 mm.

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T. graybulliensis from the Clarkforkian (Cf-2) are morphologicallyvery similar to the early Wasatchian specimen. Both I1s are tooworn to assess how developed the posterocone or lateroconulewere, yet the development of the anterocone andmediocone in UM39927 is similar to that of USNM 461201 in having a relativelylarger mediocone than that of D. szalayi (Fig. 15G-I) and isolatedteeth from Big Multi Quarry (see Chester and Beard, 2012). Anisolated I1 attributed to T. graybulliensis from the early Wasatchian(USNM 512778) is less worn than the Clarkforkian specimens, andshows a distinct lateroconule and a bulge in the place of theposterocone. Although this specimen is fairly narrow comparedwith what has been documented previously for T. graybulliensis, itstill clearly represents the species and differs from D. szalayi inhaving a more pronounced mediocone and lateroconule.

UM 36199 (Fig. 16AeD) is a right M2 that represents the earliestoccurrence of Tinimomys (Cf-1). This tooth is larger than average forT. graybulliensis, but within the size range and morphologicalvariability known for this species. The lack of apical wear on thecrown, and the lack of roots and some borders of the crown, suggestthat this tooth may have still been developing in the crypt.

Three of the four more complete dentaries of T. graybulliensisfrom the Clarkforkian (Cf-2 and Cf-3) preserve enough of the lowerjaw to measure mandibular depth below P4 (see Fig. 16EeJ). Thesespecimens have slightly deeper dentaries than all measuredWasatchian specimens of T. graybulliensis from the Bighorn Basin.Clarkforkian specimens also have a P3 that is relatively smallcompared with M1 (yet they are within the lower end of the sizerange for Eocene T. graybulliensis).

Eight new specimens of T. graybulliensis from the earlyWasatchian of the Powder River Basin, Wyoming, are within thesize range and morphological variability documented in the largesample of early Eocene (Wa-1) T. graybulliensis fromUM locality SC-

4, Bighorn Basin, Wyoming. UCM 101486 is the most completemaxillary specimen of T. graybulliensis from the Powder River Basin,and it has continuous lingual cingula on P4eM3 with a hypoconeand or pericone on P4eM2, which is diagnostic for Tinimomys(Fig. 17C,D). UCM 76918 is another maxilla of T. graybulliensis withP3e4 (Fig. 17A,B). Although this specimen lacks a P3 metacone likeT. tribos and some specimens of T. graybulliensis, it is most similar toT. graybulliensis in overall tooth dimensions, in having a wide P3

protocone lobe, and in having a short and less vertical preparacristaon P4.

Three partial dentaries, (UCM 62749, Fig. 17EeG; UCM 65916;UCM 76919) preserve at least one premolar or molar, as well as apartial I1 that is elongate and mediolaterally compressed as inT. graybulliensis. Two dentaries with P4eM3 (UCM 62749, Fig. 17EeG; UCM 62762, Fig.18A,B) represent the most complete dentaries ofT. graybulliensis from the Powder River Basin and are extremelysimilar to specimens of this species from SC-4, although some haveslightly greater mandibular depth under P4.

UCM 70619 is a partial dentary of T. graybulliensis with anerupting M3 (Fig. 17HeK). The crowns of M1 and M2 have alreadyerupted, but were broken away and are only represented by roots atpresent. The dentary is broken slightly mesial to the mesial root ofM1, although the broken distal root of dP4 can be differentiatedfrom the crown of P4 that was still developing in the crypt (Fig. 17J).The crown of M3 is unworn and similar to other specimens ofT. graybulliensis in having three distinct trigonid cusps, but differs inhaving a slightly longer and broader hypoconulid (approaching thelobate condition of some paromomyids).

Discussion: The late Paleocene sample of T. graybulliensis re-ported here includes the oldest known occurrence of this species(earliest Clarkforkian, Cf-1). This specimen, an isolated M2 (UM36199), was recovered from a limestone from UM locality SC-179 inthe Bighorn Basin, which until recently was the lowest documentedoccurrence of rodents on Polecat Bench, and possibly the oldestoccurrence of rodents in North America (Bloch, 2001; although seeDawson and Beard, 1996; Secord, 2008).

New Clarkforkian specimens of T. graybulliensis are very similarto those previously known from the early Eocene, although theyappear to differ in having greater dentary depth below P4. Tinim-omys is unique among micromomyids in having a dentary thatgradually increases in depth until it reaches its maximum depthbelow P4, whereas other micromomyids have a dentary that ismore uniform in depth (Beard and Houde,1989). The new dentariesof T. graybulliensis from the Clarkforkian are evenmore exaggeratedin mandibular depth below P4, although sample size is small(n ¼ 3). It is unclear whether this morphological difference relatesto diet, but the crowns of the teeth preserved in these specimens donot appear to differ from those of Wasatchian specimens ofT. graybulliensis in any appreciable way.

New specimens of T. graybulliensis from the Wasatchian of thePowder River Basin are also very similar to those previously knownfrom theWasatchian of the Bighorn Basin. One notable difference isthe slightly longer and considerably broader hypoconulid of M3 inUCM 70619 (Fig. 17I). We attribute this difference to variabilitygiven that this tooth position represents one of the more variableregions of the toothrow (Gingerich, 1974), and that this specimen isfound co-occurringwith another specimen of T. graybulliensis (UCM62762; Fig. 18A,B) at locality UCM 2010009. Even with over onehundred micromomyid plesiadapiform specimens recovered fromfreshwater limestones, UCM 70619 is the first knownmicromomyidspecimen with erupting teeth. UCM 70619 demonstrates that M1and M2 erupt before M3, and that M3 erupts before P4. This spec-imen is between stages 2 and 3 of Bloch et al. (2002; see fig. 6) andsuggests that micromomyids have a similar dental eruptionsequence to that of paromomyid plesiadapiforms.

Table 2Summary of dental measurements (in millimeters) for Tinimomys graybulliensisfrom SC-4.

Tooth N OR x SD CV

P3L 9 0.89e1.06 0.97 0.06 5.83P3W 9 0.49e0.69 0.61 0.07 12.06P4L 24 1.20e1.46 1.36 0.07 5.32P4W 24 0.78e0.99 0.91 0.06 6.35P4H 20 0.87e1.06 0.95 0.05 5.43M1L 20 1.05e1.22 1.12 0.04 3.35M1W 20 0.84e1.04 0.91 0.04 4.85M2L 11 1.02e1.14 1.07 0.04 3.39M2W 13 0.82e1.03 0.93 0.06 5.95M3L 15 1.30e1.55 1.43 0.06 4.41M3W 15 0.79e0.95 0.84 0.05 6.07MD 13 2.32e2.76 2.58 0.12 4.47P2L 2 0.83e0.88 0.86 0.04 4.14P2W 2 0.45e0.51 0.48 0.04 8.84P3L 11 0.96e1.15 1.07 0.06 5.65P3W 11 0.95e1.21 1.10 0.09 8.34P4L 16 1.24e1.49 1.35 0.06 4.48P4W 15 1.46e1.95 1.74 0.13 7.56M1L 20 1.02e1.13 1.07 0.03 2.46M1W 15 1.58e1.73 1.68 0.04 2.26M2L 17 0.95e1.12 1.03 0.05 4.53M2W 17 1.55e1.75 1.64 0.06 3.70M3L 9 0.71e0.96 0.85 0.08 8.89M3W 9 1.34e1.65 1.49 0.10 6.53

L, length; W, width; H, height; MD, mandibular depth below distal root of P4; N,sample size; OR, observed range; x, mean; SD, standard deviation; CV, coefficient ofvariation.

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Validity ofMyrmekomomys loomisi: Robinson (1994) proposed anew genus and species, M. loomisi, based on two specimens fromthe early Eocene of the Powder River Basin, Wyoming (Fig. 18CeF).He also reported three specimens of T. graybulliensis in the PowderRiver Basin, and one of these specimens was collected at the fossillocality where the holotype of M. loomisi was recovered. Robinson(1994) suggested that Myrmekomomys differs from Micromomysin having more lingually placed trigonids on the lower molars, anddiffers from all known micromomyids in having a more elongateM3 hypoconulid and higher crowned lower molars. He also notedthatM. loomisi is similar to T. graybulliensis in having a trigonid thatis lingually situated, and claimed that M. loomisi differs fromT. graybulliensis in having relatively greatermolar trigonid relief anda taller talonid, M1 larger than M2, M1e2 hypoconulids that aremore developed, and an M3 hypoconulid that is relatively narrow,elongate, and tall (Robinson, 1994). However, Rose and Bown(1996) argued that characters used to distinguish Myrmekomomysfrom Tinimomys did not validate generic separation.

New specimens of micromomyids reported here from thePowder River Basin, as well as the large Wa-1 sample ofT. graybulliensis from UM locality SC-4 in the Bighorn Basin, allowus to assess the diagnosis ofM. loomisi. All micromomyid specimensfrom the Powder River Basin that preserve lower molars havesimilarly oriented trigonids with lingually situated paraconids(except UCM 54585 that is attributed to C. antelucanus above).Robinson (1994) claimed that Tinimomys has relatively low-crowned molars (M1 trigonid 1.5 times taller than talonid) withmuch less relief than those of Myrmekomomys (M1 trigonid twotimes taller than talonid). However, the only illustrated specimenthat was considered to be T. graybulliensis is UCM 48620, a partialdentary with P4 and an extremely worn M1 (Robinson, 1994).Comparisons with less worn T. graybulliensis molars from the newPowder River Basin sample and the UM locality SC-4 sample showthat the specimens attributed to M. loomisi are within the range ofvariation of molar height for T. graybulliensis (Fig. 18). Robinson(1994) also noted that M1 is larger than M2 in his diagnosis forM. loomisi, although this is also virtually always true forT. graybulliensis. The development of the hypoconulids on M1e2 ofthe two specimens previously attributed to M. loomisi also fallwithin the variability of this feature in the new Powder River Basinand SC-4 samples of T. graybulliensis (Fig. 18).

The only feature present in ‘M. loomisi’ that is outside the vari-ability documented for T. graybulliensis is the expression of the M3hypoconulid. As noted by Robinson (1994), the M3 hypoconulid inthe holotype of M. loomisi (UCM 48544; Fig. 18D) is narrower,elongate, and tall compared with the more broad, low-crowned M3hypoconulid of T. graybulliensis. Specimens of T. graybulliensis (suchas UCM 62749, Fig. 17EeG; 62762, Fig. 18A,B) and the secondspecimen originally referred toMyrmekomomys in the sample fromthe Powder River Basin (UCM 52038; Fig. 18E,F), have somewhatwider molars than those of the holotype ofM. loomisi. The presenceof such a narrow hypoconulid in the holotype of M. loomisi mayrelate to the general narrowness of the lower molars of thisparticular individual. The erupting M3 in UCM 70619 (Fig. 17I) hasan especially broad hypoconulid that falls outside of the morpho-logical variability known for T. graybulliensis. It may not be a coin-cidence that this is also the only feature that differs from the largesamples of T. graybulliensis in the specimens originally attributed toM. loomisi. Again, expression of the M3 hypoconulid may be espe-cially variable because it is a feature on a tooth locus that has beendemonstrated to be quite variable in size (Gingerich, 1974). Addi-tionally, all of the new specimens from the Powder River Basin,including upper teeth, appear to belong to T. graybulliensis and lackunique morphological features that one might expect if anotherdistinct species was present. Dental measurements of all new

specimens from the Powder River Basin fall within the rangedocumented in the SC-4 T. graybulliensis sample (Table 2). Wetherefore considerMyrmekomomys a junior synonym of Tinimomys,and consider the proposed species M. loomisi as a variant ofT. graybulliensis.

Stratigraphic record of tooth size in T. graybulliensis: The ClarksFork Basin preserves a continuous late Paleocene and early Eocenestratigraphic section, with well-documented meter levels for UMfossil localities where specimens of T. graybulliensis have beencollected (e.g., Gingerich, 2003; UM stratigraphic database). Resultsfrom plotting the area of molars (M1, M2, andM2) of T. graybulliensisagainst meter levels suggest that there was no significant shift inbody size in this species from the early Clarkforkian to the earlyWasatchian in the Bighorn Basin, Wyoming (Fig. 19). It might beexpected for T. graybulliensis to exhibit relatively small body size or‘dwarfing’ in Wa-0, the principal faunal zone of the global warmingevent knownas thePaleoceneEoceneThermalMaximum(PETM), asthis has been documented in many herbivorous and some carnivo-rous mammals during this interval (e.g., Gingerich, 1989, 2003;Heinrich et al., 2008; Chester et al., 2010; Secord et al., 2012). How-ever, this cannot be evaluated because the two isolated lowermolarspreviously attributed to T. graybulliensis from Wa-0 (Strait, 2001)represent the microsyopid Niptomomys (Fet and Strait, 2006; SGBC,Personal observation), and therefore no micromomyids are knownfrom the PETM. It is surprising that T. graybulliensis has not yet beendocumented during the PETM given that this species is found in thebracketing faunal zones, Cf-3 and Wa-1, and because many speci-mens of small-bodied mammals including the plesiadapiform Nip-tomomys and euprimate Teilhardina have been discovered in PETMstrata (e.g., Strait, 2001; Rose et al., 2011).

T. tribos Chester and Beard, 2012Holotype: CM 70062, R maxilla P4eM2.Known distribution: Middle Clarkforkian (Cf-2) of Big Multi

Quarry, Washakie Basin, Wyoming.Diagnosis: Differs from T. graybulliensis in being slightly smaller

in most tooth dimensions, having a short diastema between P2 andP3, lacking a metacone and having a mesiodistally narrower

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protocone lobe on P3, having less inflated paracone and metaconeon P4eM2, and having a parastyle on P4 that is positioned lowerrelative to the paracone, resulting in a longer, more nearly verticalpreparacrista.

Micromomyid body mass estimation

In the description of the first known micromomyid,M. silvercouleei, Szalay (1973)noted that thedentaryand teethof thistaxon were smaller than those of the smallest extant primate,Microcebus murinus. It has since become well established that adistinctive characteristic of micromomyid plesiadapiforms is theirvery small size. Size likely played a major role in the physiology andecology of these animals, so it is important to have accurate esti-mates of body mass for the species discussed here. If possible, it isbest to estimate body mass for a fossil species based on equationsderived fromvarious anatomical regions sinceproportions of dental,cranial, and postcranial elements vary across taxa (Gingerich andGunnell, 2005). Also, although teeth are commonly used for esti-mating body mass due to their abundance in the fossil record, pre-vious studies have shown that postcranial measurements performsomewhat better than dental measurements for estimating bodymass in various groups of primates (e.g., Delson et al., 2000).

Body mass was first estimated based on the size of the lower firstmolar, which does not vary considerably compared with the size ofother tooth positions (Gingerich, 1974). Choosing M1 allowed bodymass to be calculated for eight of 11 micromomyid species. The ‘pro-simian grade’ and ‘all primate’ regressions of Conroy (1987), and the‘small mammals’ and ‘primate’ regressions of Legendre (1986) wereused (see Table 3). Body mass was also estimated for the two micro-momyid species for which dentally-associated postcrania are known(T. graybulliensis and D. szalayi). Humeral and femoral length andmidshaft diameter regressions of Gingerich (1990) were used forT. graybulliensisandD. szalayias an independent source toevaluate theresulting values of the four regression equations for M1. Isolated hu-meri previously attributed to T. graybulliensis and C. antelucanus(Beard,1989) are not considered here because they differ significantlyin morphology from dentally-associated humeri of T. graybulliensisand D. szalayi, and likely do not belong to Micromomyidae.

The results of all four M1 regression equations suggest thatmicromomyid plesiadapiforms were approximately 4e40 g. The‘prosimian grade’ and ‘all primate’ regression equations of Conroy(1987) produced fairly similar intermediate values (9e16 g),whereas the ‘small mammals’ and ‘primate’ regression equations ofLegendre (1986) produced considerably smaller (4e7 g) and larger(24e40 g) values, respectively. Previously estimated weights ofT. graybulliensis (81 g and 86 g; Conroy, 1987) are too high becausethe incorrect logged value is listed for M1 area (the same value iscorrectly listed for the larger euprimate Teilhardina americana).Results calculated in this study suggest a general trend with moreprimitive micromomyids (Foxomomys and Chalicomomys) beingsmaller than more derived taxa such as Dryomomys and Tinimomys(see cladistic results below). Also, within these more derivedgenera, the older and more primitive species such as D. millenniusand T. tribos tend to be smaller than the younger and more derivedspecies, such as D. szalayi and T. graybulliensis. However, it shouldbe noted that these apparent trends are based on very small samplesizes of M1 for several species of micromomyids (Table 3).

Figure 19. Stratigraphic record of tooth size of Tinimomys graybulliensis from the earlyClarkforkian to the early Wasatchian in the Clarks Fork Basin, Wyoming. M1 (A), M2 (B),and M2 (C) are tooth positions that are known not to vary considerably in size. Thesetooth loci were chosen to illustrate that tooth size of T. graybulliensis in the latestPaleocene and early Eocene falls within the range of variation documented in the largesample of early Eocene T. graybulliensis from UM locality SC-4 (Wa-1; 1570 m). Mean isrepresented by black squares. Error bars show two standard deviations from the mean.

Table 3Summary of body mass estimates (g) for species of micromomyid plesiadapiforms based on regressions of average lower first molar area.

Taxon N M1L x M1L SD M1W x M1W SD Prosimian Reg. (g) All Primate Reg. (g) Small Mammal Reg. (g) Primates Reg. (g)

F. fremdi 2 1.13 e 0.78 e 12 10 5 28F. vossae 1 1.08 e 0.76 e 11 9 4 24F. gunnelli e e e e e e e e e

M. silvercouleei e e e e e e e e e

C. antelucanus 3 1.04 0.03 0.80 0.02 11 9 4 25D. millennius 1 1.11 e 0.90 e 14 13 6 36D. dulcifer 4 1.06 0.09 0.96 0.06 15 13 6 37D. szalayi 1 1.11 e 0.96 e 16 14 7 40D. willwoodensis e e e e e e e e e

T. tribos 5 1.03 0.04 0.90 0.03 13 11 5 31T. graybulliensis 33 1.13 0.04 0.93 0.05 16 14 6 39

Average first molar area was calculated by multiplying the first lower molar maximum length (M1L) and width (M1W). Standard deviation (SD) was calculated for M1L andM1W, however, this does not account for error of the regression coefficients. Prosimian Reg., Prosimian regression of Conroy (1987); All Primate Reg., All-primates regressionof Conroy (1987); Small Mammal Reg., Small mammals (<500 g) regression of Legendre (1986); Primates Reg., Primates (data from Gingerich et al., 1982) regression ofLegendre (1986).

Figure 20. Phylogenetic hypothesis for interrelationships among micromomyid ple-siadapiforms based on a strict consensus of three most parsimonious trees (seeAppendices B and C). Best tree score ¼ 51; CI ¼ 0.765; RI ¼ 0.806; RC ¼ 0.617;HI ¼ 0.275. Unambiguous synapomorphies with superscript R indicating instances ofreversal: Node 1 (Micromomyidae), 4(1), 7(1), 8(1), 13(1), 14(1); Node 2, 1(1), 5(1),9(1); Node 3, 20(1); Node 4, 28(1); Node 5 (Tinimomys) 6(2), 8(0)R, 11(1), 17(3), 19(1),27(1); Node 6 (Dryomomys), 3(1), 4(2), 21(1), 22(1), 23(2), 24(1), Node 7, 11(0)R, 16(1),26(1).

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The results of all four postcranial regression equations suggestthat T. graybulliensis and D. szalayi were 13e32 g and 13e35 g,respectively. USNM 461201 is a partial skeleton of T. graybulliensiswith a fully erupted adult dentition, including M1 that is very closein size to the average for this species. It preserves both humeriwithout fused proximal epiphyses, as well as one isolated proximalhumeral epiphysis. The best-preserved humerus and proximalepiphysis lengths combinedwere estimated to total 14mm, and theanteroposterior midshaft diameter is 1.15 mm. The resulting bodymass values from the Gingerich (1990) regression equations are32 g and 23 g, respectively. The best-preserved femur of USNM461201 is missing its distal epiphysis. Based on comparisons tomore fully fused, yet less complete, isolated femora previouslyattributed to T. graybulliensis (Beard, 1989), this individual appearsto be near full adult size. Total length of the femur is estimated to be15 mm and anteroposterior midshaft diameter is 1.05 mm. Theresulting body mass values from the Gingerich (1990) regressionequations are 23 g and 13 g, respectively.

UM 41870 is the only known partial skeleton of D. szalayi and itpreserves a fully erupted adult dentition. It has a complete humeruswith a fused proximal epiphysis and a broken distal articular sur-face. The humeral length is estimated to be 14.5 mm, and theanteroposterior midshaft diameter is 1.2 mm. The resulting bodymass values from the Gingerich (1990) regression equations are35 g and 26 g, respectively. UM 41870 also preserves a femur withproximal and distal ends, although the diaphysis is broken in halfnear the proximal end. Total length of the femur is estimated to be15 mm and anteroposterior midshaft diameter is 1.05 mm. Thesevalues are the same as those of T. graybulliensis, and therefore alsoresult in a body mass estimate of 23 g and 13 g, respectively.

Bodymass estimates of micromomyids derived from postcranialregression equations (humeral, 23e35 g; femoral, 13e23 g) fallwithin the range of values from dental regression equations (4e40 g). More specifically, T. graybulliensis and D. szalayi are extremelysimilar in body mass according to dental (see Table 3) and post-cranial measurements. All micromomyids fall well below Kay’sthreshold (500 g; Kay, 1984), which suggests that these small pri-mates were partly insectivorous if this threshold for extant pri-mates also generally applies to plesiadapiforms. However, thepremolar morphology and more bunodont molar cusps of certainspecies, such as T. graybulliensis, suggest that these species had adiet also consisting of plant products such as gums (Szalay, 1974).

Phylogenetic analysis results

Three most parsimonious trees were recovered with a treelength of 51 steps, a consistency index (CI) of 0.765, a retentionindex (RI) of 0.806, a rescaled consistency index (RC) of 0.617, and a

homoplasy index (HI) of 0.275. Resulting tree topology of a strictconsensus analysis (Fig. 20) includes a polytomy at the base ofMicromomyidae consisting of the three species placed in the newgenus Foxomomys and a clade including all other micromomyidspecies. M. silvercouleei is the next most basally divergent speciesfollowed by C. antelucanus. Tinimomys and Dryomomys formrespective clades within a larger clade that is the sister group toC. antelucanus. T. graybulliensis and T. tribos are sister taxa. Thetwo species attributed to Dryomomys, D. millennius andD. willwoodensis, form amonophyletic groupingwith D. dulcifer andD. szalayi. D. millennius, the oldest species of Dryomomys, is themost basally divergent within this clade and sister to a polytomyamong the three remaining species of Dryomomys.

Discussion

Results of the cladistic analysis suggest that the three species ofthe new genus Foxomomys are the most primitive members of theMicromomyidae. This result is in accordance with previous claimsthat F. fremdi is the most primitive member of the family (e.g., Fox,1984; Beard and Houde, 1989). These species of Foxomomys do notform a clade, however the lack of synapomorphies that would

Figure 21. Phylogenetic hypothesis for interrelationships among micromomyid ple-siadapiforms placed in a stratigraphic context. Bold lines represent temporal ranges oftaxa. Genera abbreviations: F., Foxomomys; M., Micromomys; C., Chalicomomys; T.,Tinimomys; D., Dryomomys. Biozone abbreviations: Ti, Tiffanian; Cf, Clarkforkian; Wa,Wasatchian.

S.G.B. Chester, J.I. Bloch / Journal of Human Evolution 65 (2013) 109e142136

support these three species as a monophyletic group is probablydue to the fact that F. vossae and F. gunnelli are so poorly known.Based on the resulting tree topology, the genus Micromomys wasclearly polyphyletic prior to this taxonomic revision. Results alsosuggest that the type species of Micromomys, M. silvercouleei, ismore closely related to other micromomyid species than to thethree species of Foxomomys.

This result also supports maintaining a monotypic genusMicromomys because adding C. antelucanus to the genus wouldmake Micromomys paraphyletic. Secord (2008) suggested that asingle-rooted P2, lack of diastema between C1eP2, and a relativelywide P4 could be synapomorphies that unite C. antelucanus andM. silvercouleei, and differentiate them from F. fremdi. However, allof these features are also present in Dryomomys, and some arepresent in Tinimomys, indicating that they are not uniquely derivedin C. antelucanus and M. silvercouleei. Species of Dryomomys andTinimomys have several respective autapomorphies not present inC. antelucanus or M. silvercouleei, and therefore none of these spe-cies should be allocated to Chalicomomys or Micromomys.

Results also suggest that C. antelucanus is more primitive thanall species of Dryomomys and Tinimomys. C. antelucanus is onlyknown from the early Eocene, which implies a fairly long ghostlineage, with Chalicomomys diverging from more primitive micro-momyids during or before the late Tiffanian (Fig. 21). Like someother micromomyids, Chalicomomys is mainly known from fresh-water limestones. These limestones tend to preserve many smallmammals that have not been documented when surface collectingmudstones and sandstones (Bloch, 2001). Therefore, it is not thatsurprising that Chalicomomys is part of a previously unknownlineage. Long ghost lineages have been suggested for other mam-mals discovered in limestones, such as the paromomyid plesiada-piform Acidomomys hebeticus (Bloch et al., 2002).

The Dryomomys clade, which is specialized in having relativelylarge premolars, appears to have diverged from more primitivemicromomyids during or before the late Tiffanian (Fig. 21). TheTinimomys clade, which is derived in having more bunodont molarcusps, appears to have diverged from more basal micromomyidsduring or before the earliest Clarkforkian (Fig. 21). The Tinimo-myina (Tinimomys and Chalicomomys) and Micromomyina(Micromomys sensu lato) clades proposed by Beard and Houde(1989) are not supported by the results of this cladistic analysis.

General trends in the lower dentition of micromomyids includea gradual reduction of P2, with Foxomomys having a double-rootedP2, Micromomys, Chalicomomys, and Dryomomys having a single-rooted P2, and Tinimomys lacking P2. The lower premolars ofmicromomyids generally becamemore specialized than themolars,although a few trends documented in the molars are worth noting.The lower molars of Foxomomys are narrow compared with therelatively wider lower molars of other micromomyids. The lowermolars of Foxomomys are also higher crowned compared to thevarious degrees of bunodonty that independently evolved indifferent clades, such as that of D. szalayi and especially that ofT. graybulliensis. The M3 hypoconulid of Foxomomys is slightlyinflated, yet cuspate, whereas it is slightly more expanded in Cha-licomomys and Dryomomys, and considerably expanded inTinimomys.

General trends in the upper dentition of micromomyids includea relative size increase in P3 from Foxomomys to Chalicomomys toTinimomys and Dryomomys. There is also a trend away from themore primitive upper molars of Foxomomys and Chalicomomys thathave a pronounced ectoflexus and parastyle, as well as a moretransversely elongate M2 compared with M1. The most strikingexample of trends within a clade of micromomyids are those ofDryomomys, in which the lower and upper premolars appear toincrease in size, with P3e4 becoming more lingually expanded

through time. There appears to be a size increase from moreprimitive micromomyids (Foxomomys and Chalicomomys) to morederived taxa (Dryomomys and Tinimomys). Also, within the Dry-omomys and Tinimomys clades, there appears to be a size increasefrom the older and or more primitive species to the younger andmore derived species.

Conclusions

New specimens of micromomyid plesiadapiforms describedhere add to our understanding of this early euarchontan radiation.Five genera and 11 species of micromomyids are recognized. Thenew genus Foxomomys is erected to reflect shared differences be-tween three Tiffanian species (F. fremdi, F. vossae, and F. gunnelli)and all other micromomyids, including the type species ofMicromomys, M. silvercouleei. ‘Micromomys’ millennius and ‘M.’willwoodensis are attributed to Dryomomys primarily on the basis ofhaving relatively large premolars. Myrmekomomys loomisi is notrecognized as a distinct genus or species, and is considered a juniorsynonym of T. graybulliensis. The first major cladistic analysis toassess micromomyid interrelationships was performed, and a fairlywell resolved strict consensus tree was obtained. Results suggestthat the three species of Foxomomys are the most basal micro-momyids known, early Eocene C. antelucanus appears to be fairlybasal (which implies a long ghost-lineage), and there is support forthe monophyly of Dryomomys and Tinimomys.

Body mass was estimated based on M1 area for eight of 11species of micromomyids, and based on humeral and femoralmeasurements for two species. Results suggest that these micro-momyid species were 4e40 g. Small body size suggests thatmicromomyids were partly insectivorous, although certain species

S.G.B. Chester, J.I. Bloch / Journal of Human Evolution 65 (2013) 109e142 137

have fairly bunodont dentitions and probably mainly consumedplant products. No apparent change in body size was documentedfrom the late Paleocene to the early Eocene in the best-knownmicromomyid species, T. graybulliensis. However, no specimens ofT. graybulliensis are known from the PaleoceneeEocene ThermalMaximum (faunal zone Wa-0), a global warming event that iscorrelated with body size changes in other mammals.

Like some other plesiadapiforms, micromomyids have reducedtheir dental formula mesially (except their central incisors),specialized their antemolar teeth (especially the third and fourthpremolars), retained fairly conservative molars, and appear to havegenerally increased in body size over time. The molars of micro-momyids are very similar to those of early euprimates, such as theprimitive omomyid Teilhardina, and suggest primate affinities. Assuggested by the fairly plesiomorphic Eocene form, C. antelucanus,the micromomyid taxa known thus far likely represent just aglimpse of a more expansive radiation. The current spotty distri-bution of micromomyids through space and time is probably partlydue to their small size, and the recovery and preparation of fresh-water limestones will continue to be important for filling in thesetemporal and geographic gaps.

Acknowledgments

For access to specimens and comparative casts, we are grateful tothe following people and institutions: Chris Beard and Alan Tabrum,Carnegie Museum of Natural History; Richard Fox, Craig Scott, andMichael Caldwell, University of Alberta Laboratory for VertebratePaleontology; Jaelyn Eberle, Toni Culver, Deb Wagner, and Peter

Appendix A. Specimen list and dental measurements in millimeter

Dimensions of I1eP2 of micromomyids analyzed.

Specimen Element Locality Taxon

USNM 516587 L max P2eM3 UM SC-4 C. antelucanus e

UM 110140 L max P2eM1 Y2K Quarry D. millennius e

UM 41870 Palate I1eM3 UM SC-327 D. szalayi 1UM 39927 L premax I1e2 UM SC-117 T. graybulliensis 1UM 39929 L I1 UM SC-117 T. graybulliensis e

UM 85176 R P2, 3 UM SC-327 T. graybulliensis e

USNM 461201 Palate L I1e2, R P2eM3 UM SC-26 T. graybulliensis 1USNM 512233 L max P2eM3 UM SC-4 T. graybulliensis e

USNM 512237 L max P2eP4 UM SC-4 T. graybulliensis e

USNM 512778 R I1 UM SC-4 T. graybulliensis 1CM 69337 P2 CM 2433 T. tribos e

Dimensions of P3eM3 of micromomyids analyzed.

Specimen Element Locality Taxon P

USNM 425588 R max P3e4, M2e3 UM SC-4 C. antelucanus 1.USNM 512241 R M2 UM SC-4 C. antelucanus e

USNM 512258 R P4 UM SC-4 C. antelucanus e

USNM 512261 R M1 UM SC-4 C. antelucanus e

USNM 516587 L max P2eM3 UM SC-4 C. antelucanus 1.Averages P3e4, M2e3 CM 2433 D. dulcifer 1.UM 110140 L max P2eM1 UM SC-278 D. millennius 1.UM 39849 R P4 UM SC-19 Dryomomys sp. e

UM 41870 Palate I1eM3 UM SC-327 D. szalayi 1.UALVP 21014 L max P4eM3 UADW-2 F. fremdi e

UALVP 21015 L max P2eM3 UADW-2 F. fremdi 0.UCM 101486 L max P4eM3 UCM 20044086 T. graybulliensis e

UCM 76918 L max P3eP4 UCM 89079 T. graybulliensis 1.

Robinson, University of Colorado Museum of Natural History; PhilipGingerich and Gregg Gunnell, Museum of Paleontology, University ofMichigan; Mark Florence, Robert Purdy, and Michael Brett-Surman,National Museum of Natural History; Eric Sargis and Chris Norris,Peabody Museum of Natural History; Suzanne Strait, Marshall Uni-versity; Ross Secord, University of Nebraska StateMuseum; and PeterHoude, New Mexico State University. We thank Mary Silcox and twoanonymous reviewers for comments that improved the manuscript.We also thank Eric Sargis for reading a previous version of thismanuscript, and Chris Beard, Doug Boyer, Richard Fox, Richard Hul-bert, Eric Sargis, Ross Secord, Mary Silcox, and Gabe Yapuncich forhelpful discussions. A portion of this manuscript was revised whenJ.I.B. was supported as an Edward P. Bass Distinguished VisitingEnvironmental Scholar in the Yale Institute for Biospheric Studies(YIBS). For assistance with micro-CT scanning, we thank Josh VanHouten, Department of Internal Medicine, Yale University. We alsothank Jason Bourque for preparation of specimens, Zachary Randallfor generating digital images for Figs. 11e14, and David Reed foraccess to the Visionary Digital (Palmyra, Virginia) System providedby the National Science Foundation (DEB 0845392) at the FLMNH.Research was primarily funded by the National Science Foundation(SBE-1028505 to E.J. Sargis and S.G.B.C., and SBR-9616194 to G.F.Gunnell, P.D. Gingerich, and J.I.B.) and the Leakey Foundation(Research Grant to S.G.B.C). S.G.B.C. also acknowledges fundingsupport from the Theodore Roosevelt Memorial Grant, AmericanMuseum of Natural History; the American Society of MammalogistsGrants-in-Aid of Research; Sigma Xi Grants-in-Aid of Research;Department of Anthropology Williams Fund Grant, and a John F.Enders Fellowship, Yale University.

s. Illustrations of measurements can be found in Fig. 3.

I1L I1W I1H I2L I2W C1L C1W P2L P2W

e e e e e e 0.80 0.47e e e e e e 0.80 0.53

.14 0.64 1.77 0.96 0.58 1.03 0.55 1.03 0.70

.19 0.70 1.62 0.98 0.57 e e e e

0.69 e e e e e e e

e e e e e e 0.83 0.48.21 0.73 1.81 1.00 0.52 e e 0.81 0.51

e e e e e e 0.88 0.51e e e e e e 0.83 0.45

.08 0.64 e e e e e e e

e e e e e e 0.88 0.40

3L P3W P4L P4W M1L M1W M2L M2W M3L M3W

13 0.96 1.30 1.54 e e 0.97 1.56 0.79 1.55e e e e e 0.97 1.40 e e

e 1.20 1.34 e e e e e e

e e e 0.95 1.59 e e e e

15 1.00 1.24 1.54 0.98 1.47 0.93 1.60 0.88 1.5828 1.19 1.44 1.86 e e 0.86 1.37 0.81 1.3920 1.19 1.28 1.55 0.85 1.35 e e e e

e e 1.65 e e e e e e

39 1.45 1.33 1.94 0.94 1.45 0.91 1.42 0.88 1.52e e e e e e e e e

72 0.55 1.26 1.60 1.07 1.57 1.08 1.69 0.97 1.55e 1.36 1.90 1.07 1.72 1.03 1.64 0.87 1.52

05 1.02 1.43 1.87 e e e e e e

(continued on next page)

(continued )

Specimen Element Locality Taxon P3L P3W P4L P4W M1L M1W M2L M2W M3L M3W

UM 36199 R M2 UM SC-179 T. graybulliensis e e e e e e 1.08 1.68 e e

UM 39880 R M1 UM SC-117 T. graybulliensis e e e e 1.10 1.61 e e e e

UM 39881 L M2 UM SC-117 T. graybulliensis e e e e e e 1.02 1.69 e e

UM 71030 L M1e3 UM SC-188 T. graybulliensis e e e e 0.94 1.58 1.03 1.61 e e

UM 75602 R max P3eP4 UM SC-38 T. graybulliensis e e 1.36 1.75 1.10 1.66 1.05 1.61 0.92 1.50UM 76009 L M2 UM SC-54 T. graybulliensis e e e e e e 1.07 1.67 e e

UM 76924 R M2 UM SC-29 T. graybulliensis e e e e e e e e e e

UM 85176 R P2, P3 UM SC-327 T. graybulliensis 0.99 1.00 e e e e e e e e

USNM 425564 R max P3eM3 UM SC-4 T. graybulliensis 1.09 1.20 1.30 1.79 1.05 1.68 1.01 1.61 0.81 1.42USNM 425582 L edent max UM SC-4 T. graybulliensis e e e e e e e e e e

USNM 425584 L max P3eM3 UM SC-4 T. graybulliensis 1.07 1.15 1.32 1.78 1.08 1.72 1.03 1.74 0.88 1.65USNM 425585 R max P4eM1 UM SC-4 T. graybulliensis e e 1.40 1.64 1.07 1.58 e e e e

USNM 425782 L max P3eM2 UM SC-4 T. graybulliensis 1.11 1.09 1.36 1.75 1.05 1.68 0.95 1.56 e e

USNM 425783 R M1e2 UM SC-4 T. graybulliensis e e e e 1.13 e 1.03 1.62 e e

USNM 425784 L M1e2 UM SC-4 T. graybulliensis e e e e 1.08 e 1.10 1.75 e e

USNM 425786 R M1e2 UM SC-4 T. graybulliensis e e e e 1.06 1.65 0.96 1.60 e e

USNM 461201 Palate L I1e2, R P2eM3 UM SC-26 T. graybulliensis 1.07 1.10 1.36 1.76 1.15 1.71 1.06 e 0.92 e

USNM 461202 R max P4eM2 UM SC-26 T. graybulliensis e e e e 1.13 1.75 1.06 1.73 e e

USNM 512211 L max P4eM3 UM SC-4 T. graybulliensis e e e e 1.09 1.68 1.03 1.63 e 1.42USNM 512212 R max P3eM1 UM SC-4 T. graybulliensis 1.04 1.07 1.34 1.69 1.10 1.70 e e e e

USNM 512213 R max P3eM2 UM SC-4 T. graybulliensis 1.15 1.19 1.36 1.94 1.06 1.68 1.02 1.65 e e

USNM 512214 R max P4eM2 UM SC-4 T. graybulliensis e e 1.28 1.95 1.08 e 1.03 1.68 e e

USNM 512215 R max M1e2 UM SC-4 T. graybulliensis e e e e 1.08 1.70 1.01 1.63 e e

USNM 512216 L max M1e3 UM SC-4 T. graybulliensis e e e e 1.11 1.69 1.05 1.70 0.96 1.57USNM 512217 L max M2e3 UM SC-4 T. graybulliensis e e e e e e 1.12 1.63 0.93 1.59USNM 512218 L max M1e2 UM SC-4 T. graybulliensis e e e e 1.02 1.68 1.06 1.66 e e

USNM 512232 R max P3eM2 UM SC-4 T. graybulliensis 1.12 1.21 1.49 1.88 1.03 1.70 0.98 1.62 e e

USNM 512233 L max P2eM2 UM SC-4 T. graybulliensis 1.09 1.16 1.38 1.84 1.06 1.73 1.06 1.71 e e

USNM 512234 L max M2 UM SC-4 T. graybulliensis e e e e e e e e e e

USNM 512235 R max M1e2 UM SC-4 T. graybulliensis e e e e e e 0.96 1.55 e e

USNM 512236 L max P4eM1 UM SC-4 T. graybulliensis e e 1.35 1.71 1.10 1.73 e e e e

USNM 512237 L max P2e4 UM SC-4 T. graybulliensis 1.02 0.97 e e e e e e e e

USNM 512248 R P4 UM SC-4 T. graybulliensis e e 1.38 1.77 e e e e e e

USNM 512249 L P4 UM SC-4 T. graybulliensis e e 1.29 e e e e e e e

USNM 512251 R P4 UM SC-4 T. graybulliensis e e 1.24 1.66 e e e e e e

USNM 512253 R M1 UM SC-4 T. graybulliensis e e e e 1.09 e e e e e

USNM 512256 L M3 UM SC-4 T. graybulliensis e e e e e e e e 0.89 e

USNM 512257 L M3 UM SC-4 T. graybulliensis e e e e e e e e 0.82 1.51USNM 512259 R M1 UM SC-4 T. graybulliensis e e e e 1.06 e e e e e

USNM 512267 L M3 UM SC-4 T. graybulliensis e e e e e e e e 0.87 1.45USNM 512269 R M1 UM SC-4 T. graybulliensis e e e e 1.08 1.64 e e e e

USNM 512273 R P4 UM SC-4 T. graybulliensis e e 1.39 1.68 e e e e e e

USNM 512274 R M3 UM SC-4 T. graybulliensis e e e e e e e e 0.71 1.34USNM 512280 L P4 UM SC-4 T. graybulliensis e e 1.36 1.59 e e e e e e

USNM 512281 L M3 UM SC-4 T. graybulliensis e e e e e e e e 0.80 1.50USNM 512283 L M2 UM SC-4 T. graybulliensis e e e e e e 1.04 1.55 e e

USNM 512681 L P3 UM SC-4 T. graybulliensis 0.98 1.02 e e e e e e e e

USNM 512682 R P3 UM SC-4 T. graybulliensis 0.96 0.95 e e e e e e e e

USNM 512692 L max P3 UM SC-4 T. graybulliensis 1.11 1.07 e e e e e e e e

USNM 512804 L P4 UM SC-4 T. graybulliensis e e 1.28 1.46 e e e e e e

YPM 17899 L max P4eM2 PU Bone Hill T. graybulliensis e e 1.35 1.70 1.05 1.65 0.95 1.70 e e

Averages P3eM3 CM 2433 T. tribos 1.06 1.03 1.24 1.54 1.01 1.57 0.97 1.62 0.91 1.61

S.G.B. Chester, J.I. Bloch / Journal of Human Evolution 65 (2013) 109e142138

Dimensions of I1eP3 of micromomyids analyzed.

Specimen Element Locality Taxon I1L

USNM 425589 L dent P3eM2 UM SC-4 C. antelucanus e

CM 71657 R P3 CM 2433 D. dulcifer e

UM 109659 R dent P3eM2 Y2K Quarry D. millennius e

UM 41870 R dent I1eM3 UM SC-327 D. szalayi 1.2UALVP 21010 L dent C1eM3 UADW-2 F. fremdi e

UALVP 21011 R dent C1, P3eM3 UADW-2 F. fremdi e

UALVP 21013 R dent P3e4, M2e3 UADW-2 F. fremdi e

UCM 62749 R dent I1, P4eM3 UCM 84117 T. graybulliensis 1.6UCM 65916 R dent I1, P4 UCM 91056 T. graybulliensis 1.4UCM 76919 R dent I1, M1 UCM 89079 T. graybulliensis 1.6UM 39883 L dent I1eM1, M3 UM SC-117 T. graybulliensis 1.4UM 39933 R I1, dent P3eM3 UM SC-117 T. graybulliensis e

UM 82683 R dent I1, P4eM3 UM SC-62 T. graybulliensis 1.6UM 85176 R dent P3eM3 UM SC-327 T. graybulliensis e

I1W I1H C1L C1W P2L P2W P3L P3W

e e e e e e 0.91 e

e e e e e e 1.13 0.93e e e e e e 1.02 0.83

9 0.85 5.09 1.05 0.50 0.73 0.48 1.16 0.72e e e e 0.87 0.36 0.86 0.46e e 0.81 0.38 e e 0.92 0.48e e e e e e 0.88 e

3 0.92 e e e e e e e

6 0.83 e e e e e e e

0 0.84 e e e e e e e

1 0.82 e e e e e 0.79 0.59e e e e e e 0.81 0.60

1 0.80 e e e e e 0.86 0.58e e e e e e 0.88 0.54

(continued )

Specimen Element Locality Taxon I1L I1W I1H C1L C1W P2L P2W P3L P3W

USNM 425565 L dent P3eM2 UM SC-4 T. graybulliensis e e e e e e e 0.96 0.55USNM 425566 R dent I1, P3eM3 UM SC-4 T. graybulliensis 1.41 e e e e e e 1.04 0.67USNM 425567 L dent P3eM3 UM SC-4 T. graybulliensis e e e e e e e 0.98 0.65USNM 425568 R dent P3eM3 UM SC-4 T. graybulliensis e e e e e e e 0.94 0.53USNM 425574 R dent P4eM2 UM SC-4 T. graybulliensis e e e e e e e 0.89 0.57USNM 425575 L dent P3eM3 UM SC-4 T. graybulliensis e e e e e e e 0.98 0.63USNM 425576 L dent P3eM1, M3 UM SC-4 T. graybulliensis e e e e e e e 0.97 0.69USNM 425583 R dent I1, P4eM3 UM SC-4 T. graybulliensis 1.35 0.67 e e e e e e e

USNM 461201 R dent I1eM3 UM SC-26 T. graybulliensis 1.47 0.72 4.58 1.03 0.47 e e 0.94 0.62USNM 512220 L dent P3eM2 UM SC-4 T. graybulliensis e e e e e e e 0.90 0.49USNM 512225 L dent P3e4 UM SC-4 T. graybulliensis e e e e e e e 1.06 0.68YPM 17898 R dent P3e4 PU Bone Hill T. graybulliensis e e e e e e e 1.10 0.60Average P3 CM 2433 T. tribos e e e e e e e 0.92 0.57

Dimensions of P3eM3 and mandibular depth below posterior root of P4 (MD) of micromomyids analyzed.

Specimen Element Locality Taxon P4L P4W P4H M1L M1W M2L M2W M3L M3W MD

UCM 54585 R dent P4eM1 UCM 84126 C. antelucanus 1.44 1.00 1.08 1.04 0.82 e e e e 1.99UM 76682 L dent M2e3 UM SC-123 C. antelucanus e e e e e 0.99 0.88 1.24 0.74 e

USNM 425586 R dent P4 UM SC-4 C. antelucanus 1.34 0.91 0.94 e e e e e e 1.95USNM 425587 R dent P4, M2 UM SC-4 C. antelucanus 1.35 0.9 1.08 e e 0.98 e e e e

USNM 425589 L dent P3eM2 UM SC-4 C. antelucanus 1.29 0.91 0.95 1.01 0.78 1.00 0.81 e e e

USNM 512221 L dent M1e2 UM SC-4 C. antelucanus e e e 1.07 0.79 1.06 0.83 e e 1.75Averages P4eM3 CM 2433 D. dulcifer 1.62 1.10 1.38 1.06 0.96 1.02 0.93 1.37 0.81 e

UM 109659 R dent P3eM2 Y2K Quarry D. millennius 1.54 1.21 1.30 1.11 0.90 1.09 0.95 e e 2.13UM 41870 R dent I1eM3 UM SC-327 D. szalayi 1.66 1.23 1.48 1.11 0.96 1.04 0.95 1.34 0.84 2.40YPM 17732 L dent P4 UM SC-2 D. willwoodensis 1.71 1.25 1.41 e e e e e e 2.30UALVP 21010 L dent C1eM3 UADW-2 F. fremdi 1.43 0.84 e 1.15 0.78 1.12 0.79 1.37 0.73 e

UALVP 21011 R dent C1, P3eM3 UADW-2 F. fremdi 1.39 0.77 1.10 1.11 0.77 1.15 0.79 1.37 0.71 2.39UALVP 21012 L dent P4, M2e3 UADW-2 F. fremdi 1.48 e e e e 1.18 0.84 1.40 0.85 e

UALVP 21013 R dent P3e4, M2e3 UADW-2 F. fremdi 1.41 e e e e e e 1.38 0.74 e

UM 77528 L dent P4 Schaff Quarry F. gunnelli 1.20 0.76 0.95 e e e e e e 1.90UALVP 9151 L P4 UAR2 F. vossae 1.44 0.82 1.08 e e e e e e e

UALVP 9273 L dent P4eM1 UAR2a F. vossae 1.30 0.80 e 1.08 0.76 e e e e e

YPM 17676 R dent P4, M2 Princeton Quarry M. silvercouleei 1.28 0.88 1.13 e e 1.05 0.93 e e 2.05UCM 48544 R dent M1e3 UCM 81003 T. graybulliensis (‘Myr. loomisi’) e e e 1.16 0.92 1.09 0.92 1.49 0.85 e

UCM 52038 R dent M1e2 UCM 84126 T. graybulliensis (‘Myr. loomisi’) e e e 1.18 0.98 1.09 0.97 e e e

UCM 48620 R dent P4eM1 UCM 81003 T. graybulliensis 1.40 0.96 0.99 1.14 0.94 e e e e e

UCM 62749 R dent I1, P4eM3 UCM 84117 T. graybulliensis 1.45 1.00 0.93 1.18 0.99 1.05 0.95 1.45 0.85 2.99UCM 62762 R dent P4eM3 UCM 2010009 T. graybulliensis 1.44 0.99 1.05 1.15 0.94 1.04 0.91 1.43 0.87 2.67UCM 65916 R dent I1, P4 UCM 91056 T. graybulliensis 1.38 0.98 1.02 e e e e e e 2.85UCM 70619 L dent M3 UCM 2010009 T. graybulliensis e e e e e e e 1.52 0.88 e

UCM 76919 R dent I1, M1 UCM 89079 T. graybulliensis e e e 1.24 0.99 e e e e 2.96UCM 86800 R dent M1e2 UCM 98074 T. graybulliensis e e e 1.03 0.91 0.96 0.93 e e e

UM 39877 R M2 UM SC-117 T. graybulliensis e e e e e 1.09 0.94 e e e

UM 39878 R M3 UM SC-117 T. graybulliensis e e e e e e e 1.41 0.84 e

UM 39879 R M3 UM SC-117 T. graybulliensis e e e e e e e 1.42 0.88 e

UM 39883 L dent I1eM1, M3 UM SC-117 T. graybulliensis 1.27 0.86 0.88 1.14 0.87 e e 1.47 0.86 2.86UM 39928 R M2 UM SC-117 T. graybulliensis e e e e e 1.07 0.86 e e e

UM 39931 L dent M3 UM SC-117 T. graybulliensis e e e e e e e e 0.75 e

UM 39932 R dent M2 UM SC-117 T. graybulliensis e e e e e 1.04 0.88 e e e

UM 39933 R I1, dent P3eM3 UM SC-117 T. graybulliensis 1.26 0.85 0.87 1.08 0.90 1.04 0.92 1.51 0.84 2.82UM 71015 L M2 UM SC-188 T. graybulliensis e e e e e 1.08 0.93 e e e

UM 82683 R dent I1, P3eM1 UM SC-62 T. graybulliensis 1.39 0.90 e 1.15 e e e e e e

UM 85176 R dent P3eM3 UM SC-327 T. graybulliensis 1.25 e e 1.14 0.96 1.04 0.95 1.52 0.84 e

UM 111236 L dent P2, P4 UM SC-46 T. graybulliensis e e e e e e e e e e

USNM 425561 R P4 UM SC-4 T. graybulliensis 1.38 0.98 1.01 e e e e e e e

USNM 425562 R dent P4eM3 UM SC-4 T. graybulliensis 1.46 0.99 1.03 1.22 1.04 1.14 1.01 1.48 0.87 2.67USNM 425563 L dent P4eM1 UM SC-4 T. graybulliensis 1.29 0.87 0.93 1.12 0.89 e e e e e

USNM 425565 L dent P3eM2 UM SC-4 T. graybulliensis 1.35 0.89 0.90 1.12 0.91 1.10 0.92 e e 2.56USNM 425566 R dent I1, P3eM3 UM SC-4 T. graybulliensis 1.46 0.94 1.00 1.16 0.91 1.11 0.88 e e 2.48USNM 425567 L dent P3eM3 UM SC-4 T. graybulliensis 1.43 0.93 0.95 1.15 0.96 1.09 0.93 e e 2.76USNM 425568 R dent P3eM3 UM SC-4 T. graybulliensis 1.36 0.92 0.91 1.17 0.93 e e e e e

USNM 425569 R dent P4eM2 UM SC-4 T. graybulliensis 1.40 0.99 0.99 1.13 0.94 1.09 0.99 e e e

USNM 425570 R dent P4 UM SC-4 T. graybulliensis 1.32 0.86 0.96 e e e e e e 2.64USNM 425571 R dent P4eM1 UM SC-4 T. graybulliensis 1.35 0.89 0.96 1.13 0.92 e e e e e

USNM 425572 L dent P4eM1 UM SC-4 T. graybulliensis 1.44 0.93 1.06 1.14 0.92 e e e e e

USNM 425573 R dent P4eM3 UM SC-4 T. graybulliensis 1.20 0.78 e e e 1.07 0.91 e e 2.53USNM 425574 R dent P4eM2 UM SC-4 T. graybulliensis 1.34 0.95 0.98 1.10 0.90 1.04 0.93 e e 2.61USNM 425575 L dent P3eM3 UM SC-4 T. graybulliensis 1.34 0.89 0.91 1.13 0.88 e e 1.42 0.79 2.63

(continued on next page)

S.G.B. Chester, J.I. Bloch / Journal of Human Evolution 65 (2013) 109e142 139

(continued )

Specimen Element Locality Taxon P4L P4W P4H M1L M1W M2L M2W M3L M3W MD

USNM 425576 L dent P4 UM SC-4 T. graybulliensis 1.23 0.81 0.91 e e e e e e 2.55USNM 425577 R dent P3eM1, M3 UM SC-4 T. graybulliensis 1.31 0.93 e 1.08 0.90 e e 1.42 0.79 2.65USNM 425578 L dent P4eM1 UM SC-4 T. graybulliensis 1.24 0.80 0.91 1.10 0.86 e e e e 2.32USNM 425579 R dent P4eM2 UM SC-4 T. graybulliensis 1.41 0.91 0.96 1.12 0.91 1.04 0.92 e e e

USNM 425580 R edent dent UM SC-4 T. graybulliensis e e e e e e e e e e

USNM 425581 L edent dent UM SC-4 T. graybulliensis e e e e e e e e e e

USNM 425583 R dent I1, P4eM3 UM SC-4 T. graybulliensis 1.30 0.92 0.90 1.09 0.88 1.02 0.90 1.42 0.81 2.70USNM 425785 L dent M2e3 UM SC-4 T. graybulliensis e e e e e 1.07 1.03 1.44 0.92 e

USNM 461201 R dent I1eM3 UM SC-26 T. graybulliensis 1.43 0.94 1.02 1.15 0.96 1.08 0.91 1.44 0.81 2.70USNM 461202 R dent M1e3 UM SC-26 T. graybulliensis e e e 1.17 1.01 1.12 1.02 1.50 0.90 e

USNM 512219 L dent P4eM1 UM SC-4 T. graybulliensis 1.42 0.92 0.95 1.16 0.97 e e e e e

USNM 512220 L dent P3eM2 UM SC-4 T. graybulliensis 1.33 0.86 0.87 1.08 0.84 1.04 0.82 e e e

USNM 512225 L dent P3e4 UM SC-4 T. graybulliensis 1.45 0.87 e e e e e e e e

USNM 512231 R dent P4eM1 UM SC-4 T. graybulliensis 1.39 0.99 e e e e e e e 2.47USNM 512238 R dent P4eM1 UM SC-4 T. graybulliensis 1.38 0.90 0.88 e e e e e e e

USNM 512242 L dent M3 UM SC-4 T. graybulliensis e e e e e e e 1.45 0.83 e

USNM 512252 R dent M3 UM SC-4 T. graybulliensis e e e e e e e 1.45 0.85 e

USNM 512254 L dent M3 UM SC-4 T. graybulliensis e e e e e e e 1.39 0.85 e

USNM 512255 R dent M3 UM SC-4 T. graybulliensis e e e e e e e 1.52 0.91 e

USNM 512260 L M1 UM SC-4 T. graybulliensis e e e 1.11 0.87 e e e e e

USNM 512263 L M2 UM SC-4 T. graybulliensis e e e e e e 0.96 e e e

USNM 512266 L M3 UM SC-4 T. graybulliensis e e e e e e e 1.43 0.79 e

USNM 512268 R M1 UM SC-4 T. graybulliensis e e e 1.12 0.93 e e e e e

USNM 512271 L M3 UM SC-4 T. graybulliensis e e e e e e e 1.55 0.95 e

USNM 512275 L M3 UM SC-4 T. graybulliensis e e e e e e e 1.46 0.87 e

USNM 512277 R M1 UM SC-4 T. graybulliensis e e e 1.05 0.88 e e e e e

USNM 512282 L M3 UM SC-4 T. graybulliensis e e e e e e e 1.37 0.81 e

USNM 512285 L M2 UM SC-4 T. graybulliensis e e e e e e 0.95 e e e

USNM 512772 L Mx UM SC-4 T. graybulliensis e e e e e e e e e e

USNM 512786 L M3 UM SC-4 T. graybulliensis e e e e e e e 1.30 0.86 e

USNM 516544 L dent M3 UM SC-4 T. graybulliensis e e e e e e e 1.35 0.82 e

YPM 17898 R dent P3e4 PU Bone Hill T. graybulliensis 1.35 0.90 e e e e e e e e

Average P4eM3 CM 2433 T. tribos 1.29 0.96 0.91 1.03 0.90 1.09 0.86 1.47 0.84

Appendix B. Characteretaxon matrix

Characteretaxon matrix for the phylogenetic analysis of Micromomyidae performed in this study. Missing data are coded as ‘?’. Abbrevi-ations: A, polymorphism for states 0 and 1; B, polymorphism for states 1 and 2.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

P. lowii 1 2 0 0 0 1 0 0 0 0 1 0 0 0 0 0 0 0P. janisae 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1F. fremdi 0 0 0 1 0 1 1 1 0 0 1 0 1 1 1 0 1 1M. silvercouleei 1 ? ? ? 1 0 1 1 1 1 1 ? 1 1 0 0 ? ?F. vossae 0 ? ? 1 0 1 1 1 0 1 1 0 1 1 1 ? ? ?F. gunnelli 0 ? ? ? 0 1 1 1 0 0 1 ? 1 ? ? ? ? ?D. willwoodensis ? ? ? ? 2 1 1 1 1 1 0 ? 1 ? ? ? ? ?D. szalayi 1 1 1 2 2 0 1 1 1 1 0 1 1 1 0 1 2 1D. millennius ? 2 1 2 2 1 1 1 1 1 1 1 1 1 0 0 ? ?D. dulcifer ? 2 1 2 1 1 1 1 1 1 0 1 1 1 0 1 2 1T. tribos ? 1 0 1 2 2 1 0 1 1 1 1 1 1 0 0 3 1T. graybulliensis 2 B 0 1 1 2 1 0 1 1 1 1 1 1 0 0 3 1C. antelucanus 1 ? ? 1 1 1 1 1 1 1 0 1 1 1 0 0 2 1

19 20 21 22 23 24 25 26 27 28

P. lowii 0 0 0 0 1 0 0 0 1 0P. janisae 0 0 ? ? ? 0 0 0 0 0F. fremdi 0 0 0 0 0 0 0 0 0 0M. silvercouleei 0 0 ? ? ? ? ? ? ? ?F. vossae ? ? ? ? ? ? ? ? ? ?F. gunnelli ? 0 ? ? ? ? ? ? ? ?D. willwoodensis 0 ? ? ? ? ? ? ? ? ?D. szalayi 0 1 1 2 2 1 1 1 0 1D. millennius 0 1 1 2 2 1 1 0 0 ?D. dulcifer ? ? ? 2 2 1 1 1 0 ?T. tribos 1 1 0 A 1 0 1 0 1 1T. graybulliensis 1 1 0 1 1 0 1 0 1 1C. antelucanus 0 1 0 0 1 0 1 0 0 0

S.G.B. Chester, J.I. Bloch / Journal of Human Evolution 65 (2013) 109e142140

S.G.B. Chester, J.I. Bloch / Journal of Human Evolution 65 (2013) 109e142 141

Appendix C

Descriptions of dental and gnathic characters used in the cla-distic analysis.

1. Number of alveoli for P2: (0) 2 alveoli; (1) 1 alveolus; (2) P2absent.

2. P3 length/width: (0) narrow (>1.85); (1) intermediate (1.40e1.85); (2) wide (<1.40).

3. P3 area/M1 area: (0) small (<0.7); (1) large (>0.7).4. P4 area/M1 area: (0) small (<1); (1) intermediate (1.0e1.7); (2)

large (>1.7).5. P4 length/width: (0) narrow (>1.55); (1) intermediate (1.40e

1.55); (2) wide (<1.40).6. P4 length/lingual height: (0) tall (<1.15); (1) intermediate

(1.15e1.35); (2) bunodont (>1.35).7. P4 trenchant (very distinctive) paracristid: (0) absent; (1)

present.8. P4 paraconid: (0) present; (1) absent.9. P4 cristid obliqua: (0) distinctly climbs postvallid for short

distance; (1) does not climb postvallid.10. P4 mesiodorsal slope along paracristid in buccal view: (0)

gradual slope; (1) distinct break in slope.11. P4 distobuccal base: (0) slightly distended (gradual, slight

distension from mesiobuccal to distobuccal base on alveolarrim); (1) moderately distended (considerable dip from mesio-buccal base to lower distobuccal base on alveolar rim).

12. M1 length/width: (0) narrow (>1.4); (1) wide (<1.4).13. Overall size based on M1 or M2 area, or their respective alveoli:

(0) M1 or M2 area (>2 mm2); (1) M1 or M2 area (<2 mm2).14. M1 and or M2 paracristid: (0) weakly flexed; (1) strongly flexed.15. Lowermolar protoconid height relative tometaconid height (0)

subequal or protoconid slightly taller; (1) protoconid consid-erably taller.

16. M2 paraconid: (0) lingually situated; (1) centrally situated.17. M3 hypoconulid: (0) cuspate; (1) slightly inflated, yet cuspate,

narrow, and fairly distinct from hypoconid; (2) extension fromhypoconid and entoconid that tapers distally; (3) wide, distallyprojecting expansion.

18. M3 length relative to M1 length: (0) similar length; (1) M3relatively elongate.

19. Mandibular depth: (0) uniform in depth; (1) increases mesiallyto reach a maximum depth under P4.

20. Position of mesial mental foramen on dentary: (0) below P2; (1)below P3.

21. P2 area/M1 area: (0) small (<0.3); (1) large (>0.3).22. P3 protocone: (0) small cusp or cuspule; (1) distinct cusp on

expanded protocone lobe (2) large, distinct cusp on expandedand lingually extended protocone lobe.

23. P3 area/M1 and or M2 area: (0) small (<0.4); (1) intermediate(0.4e1.0); (2) large (>1.0).

24. P4 area/M1 and or M2 area: (0) small (P4/M1 < 1.65 and orP4/M2 < 1.90); (1) large (P4/M1 > 1.65 and or P4/M2 > 1.90).

25. P4 metacone: (0) distobuccal to paracone; (1) buccal toparacone.

26. P4 protocone: (0) lingually situated; (1) buccally situated.27. P4eM2 lingual cingulum: (0) absent; (1) present.28. M1 toM2width: (0) M2 relatively elongate; (1) similar inwidth.

Appendix D. Supplementary material

Supplementary material associated with this article can befound in the online version at http://dx.doi.org/10.1016/j.jhevol.2013.04.006.

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