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NewUpperPennsylvanianArmoredDissorophidRecords(Temnospondyli,Dissorophoidea)fromtheU.S.Midcontinentand...

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New Upper Pennsylvanian armored dissorophid records(Temnospondyli, Dissorophoidea) from the U.S.midcontinent and the stratigraphic distributions ofdissorophidsWilliam May a , Adam K. Huttenlocker b , Jason D. Pardo c , Jeff Benca b & Bryan J. Small da Department of Vertebrate Paleontology , Sam Noble Oklahoma Museum of Natural History ,Norman, Oklahoma, 73072, U.S.A.b Department of Biology , University of Washington , Seattle, Washington, 98195, U.S.A.c 661 Arden Lane , Pittsburgh, Pennsylvania, 15243, U.S.A.d Department of Earth Sciences , Denver Museum of Nature and Science , Denver, Colorado,80205, U.S.A.Published online: 11 Jul 2011.

To cite this article: William May , Adam K. Huttenlocker , Jason D. Pardo , Jeff Benca & Bryan J. Small (2011) New UpperPennsylvanian armored dissorophid records (Temnospondyli, Dissorophoidea) from the U.S. midcontinent and the stratigraphicdistributions of dissorophids, Journal of Vertebrate Paleontology, 31:4, 907-912, DOI: 10.1080/02724634.2011.582532

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Journal of Vertebrate Paleontology 31(4):907–912, July 2011© 2011 by the Society of Vertebrate Paleontology

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NEW UPPER PENNSYLVANIAN ARMORED DISSOROPHID RECORDS (TEMNOSPONDYLI,DISSOROPHOIDEA) FROM THE U.S. MIDCONTINENT AND THE STRATIGRAPHICDISTRIBUTIONS OF DISSOROPHIDS

WILLIAM MAY,1 ADAM K. HUTTENLOCKER,*,2 JASON D. PARDO,3 JEFF BENCA,2 and BRYAN J. SMALL4;1Department of Vertebrate Paleontology, Sam Noble Oklahoma Museum of Natural History, Norman, Oklahoma 73072, U.S.A.;2Department of Biology, University of Washington, Seattle, Washington 98195, U.S.A., huttenla@u.washington.edu; 3661 ArdenLane, Pittsburgh, Pennsylvania 15243, U.S.A.; 4Department of Earth Sciences, Denver Museum of Nature and Science, Denver,Colorado 80205, U.S.A.

Dissorophids (Olsoniformes) represent a highly terrestrialfamily of predatory temnospondyls from the late Paleozoic ofLaurasia, and are distinguished by conspicuous dorsal armoroverlying the neural spines and a hyperossified dermal skull(Carroll, 1964; DeMar, 1966; Bolt, 1974a, 1974b; Dilkes andBrown, 2007; Dilkes, 2009; Reisz et al., 2009). Although dis-sorophid diversity apparently reached its apex during the de-position of the late Early Permian (Artinskian-Kungurian) redbeds of the North American midcontinent (Carroll, 1964; De-Mar, 1966; Bolt, 1974b), the earlier temporal and spatial distri-butions of the family during the Carboniferous-Permian (C-P)transition remain unclear. More problematic, the trematopid ol-soniforms, understood by current phylogenetic studies to be thesister taxon to the dissorophids (Anderson et al., 2008a, 2008b;Reisz et al., 2009), are well represented in Upper Pennsylvaniansediments across Euramerica (Berman et al., 2010). This phylo-genetic relationship predicts that early dissorophids were presentand, given the widespread distribution of uppermost Carbonif-erous trematopids, perhaps widespread prior to the C-P bound-ary. Here, we review occurrences of purported dissorophid fos-sils from the Carboniferous and earliest Permian of the north-ern midcontinent and eastern interior United States, and reporton new collecting in Nebraska and central Oklahoma by Uni-versity of Washington Burke Museum, Denver Museum of Na-ture and Science, and Sam Noble Oklahoma Museum of NaturalHistory during summer 2009. This review reduces the significantstratigraphic and biogeographic gap that separates the Carbonif-erous and Permian diversifications of the major groups of Olsoni-formes.

Pennsylvanian Dissorophids from the Interior United States

Early records of the armored dissorophids remain sparse.With the exception of records documenting the sail-backed As-treptorhachis ohioensis from the Upper Pennsylvanian (Kasimo-vian?) Conemaugh Group of Ohio (Vaughn, 1971) and possibleremains of Platyhystrix from the Upper Pennsylvanian (Gzhe-lian) Robinson locality of Kansas (Foreman and Martin, 1988),the majority of early records of this group are known fromthe uppermost Pennsylvanian and Lower Permian of the FourCorners region of the southwestern United States, including“Aspidosaurus” (Broiliellus of DeMar, 1966, and Lucas et al.,2010), Conjunctio, Platyhystrix, and perhaps Ecolsonia (althoughthe phylogenetic affinities of Ecolsonia are controversial; e.g.,Berman et al., 2010). New records reported herein were discov-ered at two previously worked uppermost Pennsylvanian (Gzhe-lian) localities (Peru, Nebraska; and Seminole County, Okla-homa [OMNH V1005]; Fig. 1A) and constitute new tentative oc-currences of the morphologically conserved Aspidosaurus known

*Corresponding author.

previously from the Bowie and Wichita groups of north-centralTexas. Dissorophid remains were previously reported from thePeru locality of Nebraska by Ossian (1974) on the basis of twotiny (<5 mm) partial osteoderms. However, both of these frag-ments are elongate anteroposteriorly, are fused to anteroposte-riorly elongate neural spines, and display a deep vascular pit-ting more consistent with nectridean dorsal armor (A.K.H. andJ.D.P., pers. observ.) but inconsistent with dissorophid armor.Fragmentary spine material attributed to Platyhystrix was re-ported at the Robinson locality of Kansas (Wabaunsee Group)(Foreman and Martin, 1988), representing the first tenable recordof a dissorophid in the Pennsylvanian of the Kansas-Nebraska re-gion.

The current study, including some of the first unequivocal dis-sorophid records from the Pennsylvanian of the U.S. midconti-nent, is part of an ongoing revision of the C-P faunas of the north-ern U.S. midcontinent (Kansas, Nebraska) and their stratigraphiccorrelations to other well-known midcontinental localities andfaunas in Oklahoma and Texas. The new records may representa significant downward extension of the stratigraphic record ofAspidosaurus in the midcontinent (previously known from theSakmarian through Kungurian of Texas) and an important con-tribution to the sparse Pennsylvanian dissorophid record.

Institutional Abbreviations—AMNH, American Museum ofNatural History, New York; FMNH, Field Museum of NaturalHistory, Chicago; MCZ, Harvard University Museum of Com-parative Zoology, Cambridge; SNOMNH, Sam Noble OklahomaMuseum of Natural History, Norman; USNM, Smithsonian Insti-tution National Museum of Natural History, Washington D.C.;UWBM, University of Washington Burke Museum, Seattle.

LOCALITIES AND GEOLOGY

OMNH V1005

The OMNH V1005 locality (Fig. 1A) preserves abundant bonewithin a single mudstone horizon bearing concentrated pedo-genic carbonate nodules and representing a small tributary chan-nel fill deposit within the lower Ada Formation of SeminoleCounty, Oklahoma. The sedimentology and vertebrate faunawere described by Kissel and Lehman (2002). The sedimentaryfacies indicated deposition within a well-drained semiarid envi-ronment, possibly more inland in comparison to other contem-porary localities in the midcontinent, and notably did not in-clude coal swamp facies. Kissel and Lehman (2002) reported thepresence of a largely terrestrial fauna, including a temnospondyltentatively assigned to Eryops, the diadectomorph Diasparactus,the synapsid Ophiacodon, and an indeterminate sphenacodon-tian synapsid. The specimens reported here, several neural spineswith fused osteoderms assigned tentatively to cf. Aspidosaurus,were collected by one of us (W.M.) in 2009 as part of ongoing col-lecting at this locality, adding to the initial faunal list reported by

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FIGURE 1. Specimen provenance (A) and selected photographic plates of the newly collected material in stereo-pair (B–F). A, Geologic map ofPermo-Carboniferous exposures in the U.S. northern midcontinent. Light gray, Pennsylvanian system; dark gray, Permian system. B–D, SNOMNH74601 in anterodorsal (B), anterior (C), and lateral (D) views. E–F, UWBM 95000 in anterior (E) and posterior (F) views. Scale bars for B–F equal 5mm.

Kissel and Lehman (2002) and the overall terrestrial compositionof the fauna. This material represents the earliest stratigraphicoccurrence of armored dissorophids in Oklahoma, predating oc-currences of Cacops morrisi (Reisz et al., 2009) and Fayella chick-ashaensis (Olson, 1972) by as much as 25 million years.

Peru Locality

This locality (Fig. 1A) preserves bone within thin, isolatedlenses within the ‘Indian Cave Sandstone’ exposures of Peru, Ne-braska. The exposures are preserved as shear sandstone cliffs

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along an abandoned railroad right-of-way and hiking trail, fac-ing the Missouri River floodplain to the northeast of Peru. TheIndian Cave Sandstone, an informal unit, has been recently rein-terpreted as a series of disjunct incised valley fills from the upperPennsylvanian of southeastern Nebraska and Kansas (Fischbeinet al., 2009); the Peru exposures represent an incised valley fill inthe uppermost Pennsylvanian Towle Shale Member of the On-aga Formation (Admire Group). The sediments include fine- tocoarse-grained large-scale trough cross-bedded sandstones withsilty and carbonaceous lenses bearing plant, invertebrate, andvertebrate remains, representing a transitional or estuarine pa-leoenvironment. The highly disarticulated nature of the tetrapodfossils indicates some transport within the basin. The vertebratefauna was surveyed by Ossian (1974), who interpreted the faunaas a largely autochthonous estuarine or nearshore marine assem-blage dominated by actinopterygians and chondrichthyans, withfrequent occurrences of disarticulated (probably transported)terrestrial material preserving isolated remains of lungfish aswell as temnospondyls, lepospondyls, and amniotes, includingPhlegethontia, Ophiderpeton, Diploceraspis, Diplocaulus, Dendr-erpeton, Captorhinus, and indeterminate material dubiously at-tributed to dissorophids and ‘microsaurs.’ The new specimenreported here was collected by the authors in the summer of2009.

DESCRIPTION

The terminology herein largely follows that of DeMar (1966)and Bolt (1974b).

SNOMNH Material

Three isolated neural spines with fused dermal armor(SNOMNH 74601, 74602, and 74603) were discovered by one ofus (W.M.) at the Seminole County OMNH V1005 locality, andare herein referred to cf. Aspidosaurus Broili (1904). This tenta-tive identification is based on comparisons of the dermal armorof those specimens described here and others referred to As-pidosaurus, including MCZ 1258, FMNH UC 1205, and USNM22075 (DeMar, 1966:figs. 7–9); MCZ 2740 (Carroll, 1964:fig. 18);and AMNH 23412, 23418, and 23420 (pers. observ.). Shared fea-tures include an apparently single series of non-overlapping roof-shaped armor—having ventrolaterally oriented flanges—fused totheir respective neural spines.

One of the well-preserved specimens, SNOMNH 74601 (Figs.1B–D, 2C–E), includes the greater portion of the neural spinedorsal to the zygapophyses, with an overlying dermal osteodermfused to the spine. The neural spine, approximately 15 mm inheight, is medially compressed and bears paired longitudinal foreand aft ridges and a median ridge likely indicating the attach-ments of the spinal extensor muscles and interspinal ligament,respectively. The overlying osteoderms of SNOMNH 74601 and74602 are fused strongly to the neural spine. The dimensions ofthe dorsal osteoderm are approximately 14 mm in width and 12mm in anteroposterior length. The osteoderm demonstrates wellthe typical roof-like structure of Aspidosaurus, with ventrolateralflanges angled close to 90 degrees in anterior view (Figs. 1C, 2D)and a saddle-shaped, rugosely ornamented region approximately4 mm in anteroposterior length confined to the transverse midlineof the spine and having a strong transverse orientation. Thereis an unsculptured region both anterior and posterior to thisornamented region, where the bone is extremely smooth andappears faceted. The ‘facets’ may correspond to articulationsbetween successive osteoderms in individuals having well-developed armor, although they have been described as ‘non-overlapping’ by Berman and Lucas (2003), in contrast to thedouble-layered armor of Dissorophus and Cacops (Bolt, 1974b;Dilkes and Brown, 2007; Dilkes, 2009).

FIGURE 2. Line drawings of cf. Aspidosaurus UWBM 95000 (A–B)and SNOMNH 74601 (C–E). UWBM 95000 in anterior (A) and posterior(B) views. SNOMNH 74601 in lateral (C), anterior (D), and anterodorsal(E) views. Abbreviations: f, facet; fl, ventrolaterally oriented flange; ns,neural spine; s, saddle. Scale bar equals 5 mm.

UWBM 95000

An additional specimen (Figs. 1E, F, 2A, B)—an isolated neu-ral spine with a fused, dorsally located osteoderm—was recov-ered during the same 2009 field season from a poorly sorted,coarse-grained sandstone lens within fluviatile sediments of theOnaga Formation near Peru, Nebraska. The nature of the ma-trix and the incorporation of poorly preserved bony fragmentsand coarse clasts indicate that the specimen underwent substan-tial high-energy transport before final burial. Little of the neuralspine is preserved and much of the osteoderm is embedded in acoarse, highly indurated matrix (not figured), making preparationdifficult.

The exposed osteoderm is wider than in the SNOMNH spec-imens reported in the previous section. It is approximately 18.5mm in transverse width and 7 mm in anteroposterior length. Inanterior and posterior views, the angle of the lateral flanges rel-ative to the midline is relatively obtuse, approximately 120 de-grees (compared to ∼90–100 degrees in other anteriorly locatedAspidosaurus osteoderms of this type), thereby creating a shallowroof-like structure. The extremely short but wide nature of the os-teoderm superficially resembles that of Broiliellus (e.g., DeMar,1966:fig. 4). However, a tentative assignment to Aspidosauruscannot be ruled out, because there is considerable variation in As-pidosaurus osteoderms, with some being quite short with stronglytransverse lateral ridges (e.g., MCZ 2740; Carroll, 1964:fig. 18)depending on their position within the vertebral column (i.e.,

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more caudally; Berman and Lucas, 2003) or perhaps their on-togenetic stage (Bolt, 1974b). Osteoderms exhibiting this roof-like morphology have been referred to as ‘type 2’ Aspidosaurusspines by Berman and Lucas (2003). Also, unlike Broiliellus, theosteoderm is completely fused to the neural spine and the or-namentation is somewhat more restricted. Particularly, there isa narrow, ornamented ‘saddle’ bordered by anterior and poste-rior ‘facets’ (as described above for SNOMNH 74601 and 74602)that is about 2.5 mm in anteroposterior length and 18.5 mm inwidth (the entire transverse width of the osteoderm). The pre-dominantly transverse orientation of this saddle resembles ante-rior osteoderms belonging to small, possibly juvenile, specimensof Aspidosaurus (e.g., MCZ 2740; AMNH 23420); this arrange-ment differs from that of Cacops or Dissorophus, for example, inthat the ornamented region is not oriented longitudinally (as inthe latter taxa), but rather transversely and is therefore visible inlateral view. Other dissorophids, such as Broiliellus, Cacops, andDissorophus, apparently lacked this saddle-like morphology.

DISCUSSION

Taxonomic Identification and Composition of Aspidosaurus

The unique morphology of the dermal armor allows at leasta provisional assignment of the new material to the dissorophidgenus Aspidosaurus. This material represents the first tentativerecords of this genus in the northern midcontinent and per-haps the oldest known occurrences of this taxon in the United

States (i.e., if “Aspidosaurus” novomexicanus can be confidentlyreferred to Broiliellus as recommended by DeMar [1966] andBerman and Lucas [2003]). However, given the disarticulated na-ture of the referred material and the high degree of regional (andperhaps ontogenetic) variation exhibited in Aspidosaurus armor,it is not likely that the material can be resolved to the level ofspecies. Furthermore, it has been cautioned that the taxonomiccomposition of small dissorophids from the Bowie Group andyounger formations of Texas might be conflated due to separatespecies designations for specimens that might ultimately prove tobe juveniles of pre-existing taxa (Bolt, 1974b; Hook 1989). Forcompleteness, the correlation chart presented here (Fig. 3) pre-serves most currently recognized dissorophid species and, conse-quently, does not account for these potential synonymies. Thus,although it is outside the scope of this paper, we suggest that asystematic review of the Archer City dissorophids is needed inorder to better resolve the current understanding of the tempo-ral diversity of the Dissorophidae. The taxa Aspidosaurus api-calis, A. glascocki, and A. crucifer were not compared or includedin Figure 3, because the fragmentary nature of their represen-tative material caused them to be considered nomena dubia (asrecommended by Berman and Lucas, 2003). We have also ex-cluded “Broiliellus” hektotopos of the Dunkard Basin (Bermanand Berman, 1975) because the type and only specimen demon-strates a number of amphibamid synapomorphies and is likely nota member of the genus Broiliellus or of the Dissorophidae as it iscurrently diagnosed. Incidentally, “B.” hektotopos may represent

FIGURE 3. Revised stratigraphic distributions of dissorophids in the U.S. midcontinent. Asterisks represent newly reported occurrences from thePennsylvanian of the northern midcontinent. Solid bars represent observed occurrences. Dashed bars represent inferred or approximated occurrenceswhere specimen provenance is imprecisely constrained or poorly documented. Abbreviations: CH, China; CO, Colorado; KS, Kansas; NE, Nebraska;NM, New Mexico; OH, Ohio; OK, Oklahoma; RU, Russia; TX, Texas; UT, Utah. (Stratigraphic ranges and midcontinental chronostratigraphy werecompiled and updated from the following sources: Carroll, 1964; Vaughn, 1971; Olson, 1972; Ossian, 1974; Lewis and Vaughn, 1975; Foreman andMartin, 1988; Hentz, 1988; Hook, 1989; Sumida et al., 1999; Kissel and Lehman, 2002; Reisz et al., 2009; Berman et al., 2010; Lucas et al., 2010.)

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the only Permian amphibamid record from the eastern UnitedStates.

Stratigraphic Distributions of Dissorophids in the U.S.Midcontinent

The complete stratigraphic occurrences of dissorophids aresummarized in Figure 3. Previously, the earliest known dis-sorophids from the midcontinent included fragmentary materialreferred to Aspidosaurus sp. and the fragmentary Brevidorsumprofundum Carroll (1964) discovered near the Pueblo-Morancontact (Archer City Formation sensu Hentz, 1988) of ArcherCounty, Texas. However, because the Brevidorsum material con-sisted only of an incomplete skull, the presence of armor is un-certain (making impossible comparisons to the armor of Aspi-dosaurus). Furthermore, the incomplete nature of the materialhas caused some to question its placement within Dissorophidaeand suggest assignment to another dissorophoid group, such asthe Trematopidae (Hook, 1989). The oldest dissorophid armorknown from this region, three osteoderms fused to their under-lying neural spines, were collected from the lower Archer CityFormation and attributed by Carroll (1964) to the genus Aspi-dosaurus Broili based on the expanded lateral flanges, apparentfusion to the neural spine forming an inverted V-shape, and deepsculpturing along the transverse midline, a pattern consistent withthe type of A. chiton Broili (1904). Additional material has beencollected higher in the section from the Artinskian Petrolia For-mation. These specimens (MCZ 1477 and MCZ 2746) were dis-cussed and illustrated by Carroll (1964), who noted their consid-erable variation, ranging from simple, fused A. chiton-type armorto the hypertrophied Platyhystrix-type ‘spines.’ These and sim-ilarly bizarre specimens (AMNH 23412; MCZ 1477) have beenattributed variably to Aspidosaurus sp. or an Aspidosaurus-likedissorophid (e.g., DeMar, 1966; Bolt, 1974b), and consequentlyraised doubts over the presence of Platyhystrix in the midcon-tinent during this interval (Berman et al., 1981), at least in theTexas-Oklahoma region.

Biogeographic Distributions of C-P Dissorophids

The new records of cf. Aspidosaurus from the Peru andOMNH V1005 localities suggest that dissorophids comprised awidespread component of North American dryland faunas latein the Pennsylvanian, but this dissorophid diversity was largelyrestricted to platyhystricine dissorophids (e.g., Aspidosaurus,Platyhystrix, Astreptorhachis), with dissorophines and cacopinesappearing much later. The dissorophid species Platyhystrixrugosus and Aspidosaurus (Broiliellus?) novomexicanus havebeen reported from C-P boundary sequences of the El CobreCanyon Formation in Arroyo del Agua and Canon del Cobre innorthern New Mexico (Lucas et al., 2010). Platyhystrix has alsobeen reported from the C-P Cutler Group of Colorado (Lewisand Vaughn, 1975), and the latest Pennsylvanian (Gzhelian)and possibly earliest Permian (Asselian) Halgaito Formation ofUtah (Sumida et al., 1999), although it is restricted to the lowerthree-quarters of that formation (K. Scott and S. Sumida, pers.comm., 2010). These records establish firmly a Late Pennsylva-nian presence of dissorophids in the Four Corners region of thesouthwestern United States.

Within the eastern interior United States, the dissorophid As-treptorhachis ohioensis is known from the Casselman Formation(Kasimovian?) of Ohio. Astreptorhachis is known only from asingle series of dorsal vertebrae and dorsally expanded dermalarmor that is similar to that of Platyhystrix, except that the suc-cessive dermal armor elements and portions of the neural archesare fused together forming a single, rigid disk (Vaughn, 1971).In the eastern interior, the Casselman Formation represents adry interval within the cyclothems of the Dunkard Basin, andterrestrial taxa, including an archeriid embolomere (Neoptero-

plax conemaughensis) and a trematopid (Fedexia stiegeli), havebeen reported from this formation (Vaughn, 1971; Berman et al.,2010). Pollen records, paleoenvironmental interpretations, andputative drought adaptations of Fedexia (Berman et al., 2010)corroborate the interpretation that early-appearing dissorophidslived primarily in dryland or upland habitats away from the dis-tal floodplain. This hypothesis may explain the general paucity ofdissorophid fossils in deltaic deposits of the midcontinental cy-clothems prior to the C-P transition.

CONCLUSIONS

New records of dissorophid armor from the latest Pennsylva-nian of Nebraska and Oklahoma, in addition to a previous reportfrom Kansas, support the early appearance of Dissorophidae inthe U.S. midcontinent, prior to the C-P boundary. These repre-sent the oldest records of armored dissorophids in the U.S. mid-continent. However, their isolated nature possibly underscoresthe rarity of dissorophids in this low-lying region of the subconti-nent, although sampling bias cannot be ruled out. Although theirremains are extremely rare in fluviodeltaic sediments across themidcontinent, Aspidosaurus and other platyhystricines appearedin each of the physiographically diverse collecting areas of theUnited States by the latest Pennsylvanian, including the FourCorners, midcontinent, and eastern U.S. basins. We predict thatcontinued collecting in the northern midcontinent will improveour understanding of the timing and extent of the dispersal ofdissorophids and other tetrapods into new territory from the Car-boniferous into the Permian.

ACKNOWLEDGMENTS

We would like to acknowledge C. Sidor and the DinosaurFund of UWBM for logistical and travel support in Nebraska;S. Tucker and G. Corner of UNSM for logistical support and ac-cess to comparative material; R. Cifelli, J. Person, and J. Larsenof SNOMNH for access to specimens; C. Mehling and M. Norrellof AMNH for access to comparative material; D. Berman and A.Henrici of Carnegie Museum for access to comparative material;and K. Scott and S. Sumida for providing helpful discussion onbiostratigraphy of the Halgaito Formation, Utah, and relevantreferences. We also thank the handling editor J. Anderson, re-viewer R. Kissel, and an anonymous reviewer for improving themanuscript.

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Submitted February 11, 2011; accepted April 13, 2011.Handling editor: Jason Anderson.

ADDENDUM

Recent U-Pb dating of speleothems from the Richards Spurlocality, Oklahoma, indicate a probable age of 289 +/− 0.68 Ma(Woodhead et al., 2010). Thus, the Permian record of Cacopsmorrisi (Fig. 3) from this locality dates to mid-Sakmarian, andis only approximately 15 Ma younger than the presently reportedCarboniferous material.

Woodhead, J., R. Reisz, D. Fox, R. Drysdale, J. Hellstrom, R. Maas, H.Cheng, and R. L. Edwards 2010. Speleothem climate records fromdeep time? Exploring the potential with an example from the Per-mian. Geology 38:455–458.

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