First records of plesiosaur remains in the lower Smoky Hill ChalkMember (Upper Coniacian) of the Niobrara Formation in westernKansasMICHAEL J. EVERHART

Sternberg Museum of Natural History, Fort Hays State University, Hays, Kansas,67601 (meverhar@fhsu.edu)

Although plesiosaurs are known to occur in the Upper Cretaceous Smoky Hill ChalkMember of the Niobrara Formation, their remains are uncommon, rarely complete andunequally distributed in the unit. There are only three reasonably complete plesiosaurskeletons (all Dolichorhynchops osborni) known from the Smoky Hill Chalk inKansas. All three are from the upper one-third (Early Campanian) of the chalk. Otherremains are fragmentary and, in most cases, consist of body parts that could have beenreadily removed by predators or scavengers. Many of these specimens have teeth marksor appear to be partially digested. In spite of observations to the contrary by Willistonand others, reliable stratigraphic and locality information for museum specimens existsonly for plesiosaur remains in the upper portions of the Smoky Hill Chalk (Santonian -Lower Campanian). Recent discoveries reported here suggest that plesiosaurs werepresent throughout the deposition of the chalk, albeit in small numbers.

Keywords: plesiosaur, Dolichorhynchops, marine reptile, Kansas, Smoky HillChalk, Niobrara, Cretaceous, Coniacian, stratigraphy.

TRANSACTIONS OF THE KANSAS

ACADEMY OF SCIENCE

Vol. 106, no. 3/4p. 139-148 (2003)

INTRODUCTION

As a group, plesiosaurs (Sauropterygia) arewell documented in the fossil record of theWestern Interior Sea during the LateCretaceous (Cope 1868, 1869; Williston1906, 1908; Welles 1943, 1952, 1962;Russell 1993; Carpenter 1996, 1997, 1999;Storrs 1999). In Kansas, their remains includeholotypic specimens of the elasmosaurs,Elasmosaurus platyurus Cope 1868, andStyxosaurus snowii (Williston 1890); and thepolycotylids, Polycotylus latipinnis Cope1869, and Dolichorhynchops osborni(Williston 1902). All of the new specimensreported here are fragmentary and are notidentifiable with certainty beyondPlesiosauridae. From their small size andother characteristics, the remains are hereassumed to be from polycotylids and are mostlikely those of the genus, Dolichorhynchops.Samuel W. Williston (1851-1918) was

arguably the most knowledgeablepaleontologist to work in the Smoky HillChalk Member of the Niobrara Chalk between1875 and 1900. On the subject of plesiosaurs,he stated (1893, p.110) that they �are rareeverywhere, but relatively more abundant inthe lower strata.� Four years later (1897, p.245), he elaborated somewhat when he wrote:�The Plesiosaurs occur in about equalabundance throughout the deposits. They areat best comparatively rare, but relatively farmore abundant in the lower beds.� Willistonmade these statements, however, withoutciting specific specimens or localities.Although it is possible that he was referring tothe presence of plesiosaurs in the Cretaceousmarine formations below the Niobrara, hemade a point to define the �lower strata� ofthe Smoky Hill Chalk as the Rudistes Beds(1897, p. 239). Because he was one of thefirst to attempt to define the biostratigraphyof the chalk (Stewart 1990, p. 19; Everhart

2001, p. 61), it is unlikely that he wasreferring to remains from the underlying FortHays Limestone or older formations.

Both Williston (1903, p. 73-74) and Moodie(1911, p. 95) discussed the presence ofisolated embryonic and juvenile plesiosaurpropodials from the Smoky Hill Chalk but didnot provide further locality or stratigraphicinformation. Although Stewart (1990, p. 25)indicated that he was �aware of a few juvenilepropodials ... in the lowermost zones [UpperConiacian] of the Smoky Hill Chalk Member,�he saw no basis for Williston�s remarksconcerning the relative abundance ofplesiosaurs and did not document theoccurrence of plesiosaur remains lower thanthe upper one-third (Upper Santonian - LowerCampanian) of the unit.

In his survey of fossil vertebrates of Kansas,Lane (1946, p. 303-310) reviewed plesiosaurspecimens from Kansas in the University ofKansas Museum of Natural History (KUVP)and other museum collections. Among thepolycotylids from the Smoky Hill Chalk, helists (Lane 1946, p. 306) three specimens ofPolycotylus from Logan County (KUVP5916, 1308, 1312) and four from WallaceCounty (KUVP 1320, 1321, 1323 and 1324).Bennett (2000) noted that exposures of thechalk in Logan and Wallace counties are in theupper one-half of the formation (MiddleSantonian through Lower Campanian), whilethose in Rooks, Graham, Ellis, Trego andGove counties are in the lower half of theformation (Upper Coniacian through LowerSantonian). Thus, all of the KUVP specimenslisted by Lane are apparently from the upperchalk.

More recently, Storrs (1999) examinedspecimens of plesiosaurs from the NiobraraChalk of North America, and Carpenter(1996) reviewed the records of short-neckedplesiosaurs from the Cretaceous of theWestern Interior of North America. NeitherStorrs nor Carpenter reported any plesiosaurs

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from the lower two-thirds of the Smoky HillChalk. Regarding one Gove County specimen,Storrs (1999, p. 5; see also Williston 1906)concluded that Elasmosaurus sternbergiWilliston 1906 (KUVP 1312), collected byCharles Sternberg in 1895, was from theupper chalk (Santonian). Storrs (1999, p. 9)also indicated that the holotype ofDolichorhyncops osborni (KUVP 1300)came from the Smoky Hill Chalk (Campanian)of Logan County, Kansas. Carpenter (1996, p.271) concurred, noting that KUVP 1300 wascollected �east of Wallace� in Stewart�s(1990, p. 23) zone of Hesperornis. Bonner(1964, p. 41) reported the Trinacromerumosborni (FHSM VP-404; now D. osborni, perCarpenter 1997, p. 193) in the SternbergMuseum of Natural History at Fort Hays StateUniversity was collected from Logan County,a mile southwest of Russell Springs.

A third, nearly complete D. osborni specimen(MCZ 1064) collected by G. F. Sternberg(Sternberg and Walker 1957, p. 57) in 1926was also discovered in Logan County(Carpenter 1996, p. 271). Charles Sternberg(1922, p. 119; Everhart, in press) reportedpartially digested plesiosaur bones (USNM9468) as gut contents within a largeTylosaurus proriger (USNM 8898) mosasaurfrom an exposure along [Twin] Butte Creek inLogan County. The plesiosaur has beententatively identified as a juvenile polycotylid(O�Keefe, pers. com. 2001). The horizon ofall these Logan County localities is in theupper one-third (Upper Santonian throughLower Campanian) of Smoky Hill Chalk.

According to the records of the Yale PeabodyMuseum (YPM), B.F. Mudge collected theremains of a polycotylid (YPM 1643) in1875 from the Niobrara chalk in TregoCounty but no further locality information isavailable. Williston (1898, p. 31) recalled thathe and Brous assisted Mudge in collecting forYale College along the Saline and Smoky HillRivers in 1874 and 1875, most likely in Ellisand Trego Counties where Mudge had

Transactions of the Kansas Academy of Science 106(3/4), 2003 141

collected in 1873 (Peterson 1987, p. 232).Exposures of the Niobrara in Trego Countyinclude the Fort Hays Limestone and lowerone-third of the Smoky Hill Chalk (UpperConiacian to Lower Santonian). AlthoughYPM 1643 may be Upper Coniacian to LowerSantonian in age, there is not enough localityinformation available to be certain.

A review of the literature, and the collectionsin the Sternberg Museum of Natural Historyat Fort Hays State University (FHSM), theUniversity of Kansas Museum of NaturalHistory (KUVP), the Denver Museum ofNature and Science, the University ofNebraska State Museum and the United StatesNational Museum (USNM), suggests that theoccurrence of plesiosaurs in the lower onethird of the Smoky Hill Chalk (UpperConiacian) has not been previouslysubstantiated by specimens with well-documented locality or stratigraphic data.

In his discussion of the occurrence of short-necked plesiosaurs, Carpenter (1996, p. 284),determined that the genus Trinacromerum hasa 3.3-million-year range from UpperCenomanian into the Turonian, and the genusDolichorhynchops has a 4-million-year rangebeginning in the earliest Campanian. Thissuggests that there is an almost 6-million-year gap in the current fossil record of theWestern Interior Sea that is unoccupied bypolycotylids between the lower MiddleTuronian and the beginning of the Campanian.Within the Smoky Hill Chalk in Kansas, thisgap extends from the Upper Coniacianthrough the end of the Santonian. This intervalalso corresponds to the greatest expansion ofthe Western Interior Sea (Hattin 1982, p. 59),and the beginnings of the subsequentregression, a period in which the near-shore,shallow water environments, and possibly thepreferred habitats of polycotylids, were thefurthest away from the depositional area ofthe Smoky Hill Chalk in western Kansas.Here, I report on six unassociated,fragmentary plesiosaur specimens from the

Upper Coniacian of the Smoky Hill Chalk(Fig. 1) in Ellis, Gove and Lane counties,Kansas. Five of these specimens werecollected by the author between 1988 and1992, and the sixth was collected by J.D.Stewart of the Los Angeles County Museumof Natural History in my presence in 1990.Taken as a group, these specimens documentthe presence of plesiosaurs near the base ofthe chalk through the Upper Coniacian, andinto the Lower Santonian. Although notproviding a continuous record of plesiosaursthroughout the Smoky Hill Chalk (Fig. 2), thismaterial indicates their presence in much ofthe unit.

ABBREVIATIONS

The abbreviations for institutions referred toin the text are: ESU - Emporia StateUniversity Johnston Geology Museum,Emporia, KS; FHSM - Sternberg Museum ofNatural History, Fort Hays State University,Hays, KS; KUVP - University of KansasVertebrate Paleontology Collection,Lawrence, KS; LACMNH - Los AngelesCounty Museum of Natural History, Los

Figure 1. Approximate locations of fragmentaryplesiosaur specimens reported here by county:1) FHSM VP-13962, 2) FHSM VP-13963, 3)FHSM VP-13964, 4) FHSM VP-13965, 5) FHSMVP-13966, and 6) LACMNH 148920.

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Angeles, CA.; MCZ - Museum of ComparativeZoology, Harvard, Cambridge, MA; andUSNM; United States National Museum,Washington, D.C.

MATERIALS

The specimens (Fig. 3) reported here include:FHSM VP-13962 - The proximal end of animmature plesiosaur propodial, 12 cm inlength and 4 cm in maximum diameter at thebroken end; FHSM VP-13963 - A partiallydigested plesiosaur caudal(?) vertebra, 3 cmin length and 3 cm in diameter; FHSM VP-13964 - Partial (distal end) plesiosaurpropodial, 10 cm in width, 10.5 cm in lengthand 3 cm in thickness, and a smaller fragmentfrom a girdle element; FHSM VP-13965 -Three (3) plesiosaur caudal vertebrae, 2-3 cm

in diameter); FHSM VP-13966 - Fragmentsof a small polycotylid skull and lower jaws;and, LACMNH 148920 - Partial plesiosaurhind limb, including a complete femur,metapodials and phalanges.

DISCUSSION

All of these remains noted above representbody parts (head, limbs, tail) that were readilydetachable from a living plesiosaur or acarcass by large predators or scavengers.Major portions of the outer surface of thebone on all of these remains, exceptLACMNH 148920, have been eroded away ina manner that is consistent with the surfacepitting and erosion observed on partiallydigested bones. Examples include mosasaurbones apparently consumed by sharks(Shimada 1997, p. 928; Everhart 1999),plesiosaur bones reported as gut contents of aTylosaurus (Everhart, in press), and hadrosaurbones described by Varricchio (2001, p. 402-404) as gut contents of a tyrannosaurid.

Prior to these discoveries, plesiosaurs wereconspicuous by their absence in the lowerSmoky Hill Chalk of western Kansas.Although Williston (1897, p. 245-246),Bennett (2000, p. 2) and others have indicatedthat while most of the vertebrate remainsfrom the chalk now in museum collectionsare from the upper one-half of the member,the lower chalk contains as many species(Stewart 1990, p. 29-30). Based on their fieldexperience, earlier collectors also believedthat fossils from the upper chalk were morecomplete and in better condition than those inthe lower chalk. This belief has created a biasregarding collecting in the lower chalk eventhough early workers, such as Benjamin F.Mudge, discovered many specimens (Everhart2002, p. 34-35) from the more eastern(older) exposures. E.D. Cope (1872, 1875)described a number of fish and reptile typespecimens from Mudge�s lower chalkcollection.

Figure 2. Generalized stratigraphy of the SmokyHill Chalk Member showing the correlationbetween Marker Units (MU: Hattin 1982),biostratigraphic zones (Stewart 1990) and theapproximate horizon of Kansas plesiosaurspecimens.

Transactions of the Kansas Academy of Science 106(3/4), 2003 143

Propodials

FHSM VP-13962 was recovered as float on asteep slope within 10 m of the base of theSmoky Hill chalk in northwest Ellis County.The specimen represents the proximal half ofa propodial that would have been about 24 cm

in length if complete. In comparison, thehumerus of a 3 m Dolichorhynchops osborni(FHSM VP-404) is 33.6 cm in length (Bonner1964, p. 53). According to Moodie (1908, p.451), the two nutrient foramina (7 mm and 4mm diameter) located near the middle of theshaft are present only in immature specimens,

Figure 3. 1) FHSM VP-13962 - Proximal half of an immature plesiosaur propodial; 2) FHSM VP-13963 - Partially digested plesiosaur caudal vertebra; 3) FHSM VP- 13964 - Fragment of the distalend of a plesiosaur propodial; 4) FHSM VP-13965 - Three (3) plesiosaur caudal vertebrae; 5) FHSMVP-13966 - Partially digested fragments of the lower jaws (left and right articulars, surangulars, andangulars) of a small polycotylid; 6) LACMNH 148920 - Field photo of plesiosaur hind limb, includingfemur, metapodials and phalanges.

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and �disappear in the adult.� The break in theshaft is fresh and probably indicates that thebone was somewhat more complete prior toeroding out of the chalk.

FHSM VP-13964 includes a fragment of thedistal portion of a plesiosaur propodial and anassociated piece of the pectoral or pelvicgirdle that were discovered as float nearHattin�s (1982) marker unit 5 in southwestGove County. Both fragments have a corrodedexterior appearance but were not sunbleached, and did not appear to be otherwiseweathered. The fragment compares favorablyin size to the propodials of the two adultspecimens of Dolichorhynchops osborni(KUVP 1300 and FHSM VP-404).

LACMNH 148920 consists of a left femur,two podials, four other small elements, eithermetapodials or phalanges (J.D. Stewart, pers.com. 2001). It was collected in north-centralLane County, from just above Hattin�s (1982)marker unit 5. Prior to eroding out, theremains were articulated and the surface ofthe bones appeared unaltered by digestiveprocesses. Field observations indicatedserrated bite marks on the propodial that wereattributable to the shark, Squalicoraxfalcatus. Schwimmer, Stewart and Williams(1997, p. 79) noted evidence of Squalicoraxscavenging on a large variety of marinevertebrates, including Dolichorhynchops sp.(FHSM VP-12059) and Trinacromerumwillistoni (KUVP 5070, now T. bentonianum,per Carpenter 1996, p. 284).

Vertebrae

FHSM VP-13963 is a single caudal vertebra(3 cm in length by 3 cm in diameter) that wasrecovered as float near Hattin�s (1982)marker unit 1 in northwest Ellis County. Thedorsal process is missing and the surface ofthe bone appears to be acid-etched. Threesmall caudal vertebrae (FHSM VP-13965)were discovered as float in western GoveCounty, from between Hattin�s (1982) marker

unit 4 and 5. The measurements of thevertebrae are: 1) 2 cm in length by 3 cm indiameter; 2) 1.7 cm in length by 3 cm indiameter; and 3) 2 cm in length by 2.5 cm indiameter. All appear to have been partiallydigested. The dorsal processes are missingand the bone surfaces are corroded. Thevertebrae were not articulated when collectedbut all appear to have come from near the endof the tail.

Skull

Scattered elements from the back half of theskull of a single individual (FHSM VP-13966) were collected as float from justabove Hattin�s (1982) marker unit 5 insoutheastern Gove County. According to KenCarpenter (pers. com. 2001), the remainsinclude the suborbital portion of the leftmaxilla, part of the supraoccipital, a braincasefragment possibly containing a portion of theauditory meatus, a cranial fragment includingthe parietal/frontal suture, an epipterygoid,the left articular, surangular and angular, theright articular, surangular, and angular, andthree dentary fragments.

Fragmentary remains

Many fragmentary, partially digested remainsof mosasaurs have been observed by theauthor from the same Upper Coniacian chalklocalities as these plesiosaur remains. Theseare interpreted as the undigested portions ofsevered skulls, limbs and tails that were laterregurgitated by sharks. In several cases,fragmentary mosasaur remains (FHSM VP-13283, VP-13742 and VP-13746) includeembedded tooth fragments from thelamniform shark, Cretoxyrhina mantelli(Everhart 1999). The partial remains of ashark (C. mantelli, KUVP 68797) thatincludes more than a hundred gastroliths andsuggest predation or scavenging of anelasmosaur are documented from the SmokyHill Chalk (Moodie 1912, p. 377-378;Shimada 1997, p. 929; Everhart 2000, p. 69).

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In addition, Shimada (1997, p. 927) describeda specimen of Cretoxyrhina mantelli (KUVP247) that contains the remains of a 4 mXiphactinus audax as gastric contents. Inanother specimen (ESU 1047), the tip of abroken Cretoxyrhina tooth was embedded ina vertebra associated with the skull of amedium-sized Xiphactinus audax (Shimadaand Everhart, in press). Cretoxyrhina was anapex predator in the Western Interior Sea andelsewhere during Turonian, Coniacian andSantonian time, and reached lengths of 6 m(Shimada, 1997, p. 930) or more. It is likelythat they fed on plesiosaurs as well asmosasaurs and large fish.

The isolated, fragmentary plesiosaur remainsreported here apparently resulted fromfeeding activities of large predators, mostlikely Cretoxyrhina mantelli. Five of the sixspecimens show a characteristic loss of thesurface layer of bone due to corrosion bystomach acids and exhibit damage that issimilar to that visible on hadrosaur bonesidentified as gut contents of a tyrannosauridby Varricchio (2001). Subsurface bonestructures such as the �vascular canals andintertrabecular spaces have been enlarged,giving the bone a spongy appearance clearlydistinct from fresh bone� (Varricchio 2001, p.401-402). These bones are readilydistinguishable from the well preservedmarine reptile remains usually recoveredfrom the Smoky Hill chalk.

CONCLUSION

Plesiosaurs were probably present in smallnumbers in the Western Interior Seathroughout the Late Cretaceous. The scarcityof their remains from lower (UpperConiacian) Smoky Hill Chalk of the NiobraraFormation may indicate that the open, deeperwater of the middle portion of the seaway wasnot a preferred habitat for plesiosaurs. All ofthe fragmentary remains reported here arefrom plesiosaurs that appear to have beendismembered prior to burial, and possibly

represent animals that made rare crossings ofthe seaway or �bloat and float� carcasses thatdrifted in from other locations. The partiallydigested condition of most of the remainsimplicates the lamnid shark, Cretoxyrhinamantelli, as the likely predator or scavenger,although no embedded teeth or bite markshave been associated with these corrodedspecimens. The serrated bite marks ofSqualicorax have also been noted onplesiosaur remains. Further collection ofplesiosaur material from this stratigraphicinterval will enhance our understanding of thepaleoecology in the Western Interior Seaduring the Late Coniacian.

ACKNOWLEDGEMENTS

I thank Robert Purdy and Michael Brett-Surman, United States National Museum,Washington, D.C. for access to and assistancein the Smithsonian collections; KenCarpenter, Denver Museum of Science andNature, Denver, CO for his identification ofthe FHSM VP-13966 skull fragments; F.Robin O�Keefe, New York College ofOsteopathic Medicine, Old Westbury, NY forhis insight into the severely damaged remainsof USNM 9468; and J.D. Stewart, LosAngeles County Museum of Natural History,Los Angeles, CA for the data on LACMNH148920 and for sharing his knowledge of theSmoky Hill Chalk. The suggestions made bytwo anonymous reviewers improved thequality of this paper and are greatlyappreciated.

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