First polycotylid remains
from the Fort Hays Limestone
Copyright © 2009 by Mike Everhart
Created 02/09/2009 - Updated 09/18/2009
RIGHT: Dolichorhynchops osborni; Adapted from an original pen and ink drawing by Russell Hawley, used with permission.
In September, 2005, while on a weekend hunt for sharks teeth, Ramo and Pam Decker discovered large plesiosaur bones exposed at the edge of the quarry on the surface of the basal Fort Hays Limestone Member of the Niobrara Formation. The bones had been uncovered by machinery that ground up the limestone for roadbed material. Part of the specimen had already been lost and the rest would be destroyed with the next pass of the machine. Over the next two weeks, the Deckers were able to safely collect the remains. When they contacted me, I was amazed to learn of the discovery. It had been well over a hundred years since a plesiosaur had been found in the Fort Hays Limestone (coincidentally, about 15 miles south near the town of Jewell, in Jewell County), and few people since had actively collected from that rock unit. Here is a quote from Prof. B.F. Mudge, 1876, regarding this area and the long necked plesiosaur (YPM 1640 - "Elasmosaurus nobilis" Williston 1906) that he collected there:
Its fossils are Inocerami, fragments of Haploscapha [rudists], Ostrea, with occasional remains of fish and Saurians. The vertebrates are so rare that we never wasted our time in hunting them in this stratum; still, our largest Saurian, Brimosaurus of Leidy, was found in Jewell County. B.F. Mudge, 1876
Fortunately, they didn't know that they were "wasting their time" hunting fossils in the Fort Hays Limestone, and were thus able to show me not only the polycotylid plesiosaur specimen, but the other specimens of bony fish and shark teeth that they had collected from the surrounding area. They were also generous in donating the polycotylid specimen to the Sternberg Museum where it is curated as FHSM VP-16459. We presented a paper at the 2006 Annual Meeting of the Kansas Academy of Science:
*Everhart, M.J., Sternberg Museum of Natural History, R. Decker and P. Decker, Mankato, Kansas. 2006. EARLIEST REMAINS OF DOLICHORHYNCHOPS OSBORNI (PLESIOSAURIA: POLYCOTYLIDAE) FROM THE BASAL FORT HAYS LIMESTONE, JEWELL COUNTY, KANSAS.
The Fort Hays Limestone Member of the Niobrara Chalk was deposited in the Western Interior Sea during the maximum transgressive phase of the Niobrara Cyclothem (early Coniacian). The water was relatively deep, well-aerated and far enough from shore as to be beyond the influence of terrestrial sediments. The member ranges from 17-24 m in thickness and consists of several relatively resistant beds of chalky limestone separated by thin layers of chalky shale. Although rich in invertebrate remains, the Fort Hays has produced few vertebrate specimens. In 2005, polycotylid plesiosaur (Dolichorhynchops osborni) remains were collected from the basal Fort Hays in Jewell County, Kansas. The specimen (FHSM VP-16459) consists of a semi-articulated series of 24 dorsal vertebrae, pelvic and pectoral girdle fragments, ribs, and distal limb elements. Dolichorhynchops was previously known from the Campanian age Smoky Hill Chalk and Pierre Shale, although fragmentary remains of polycotylids have been reported from the upper Coniacian. The new specimen is only the second plesiosaur and the third marine reptile collected from the Fort Hays. Remains of Xiphactinus, Cimolichthys, Protosphyraena and several species of shark teeth have been collected by the authors from the same stratigraphic level. The new specimen significantly extends the temporal range of Dolichorhynchops and adds to our knowledge of the faunal diversity of the Western Interior Sea during early Coniacian time.
FHSM VP-16459 - Features:
> The remains represent an adult polycotylid, slightly larger than KUVP 1300 or FHSM VP-404, based on the size of the vertebrae.
> Almost all of the dorsal vertebrae present, including 1 or more sacrals, and a posterior cervical.
> No cranial material present
> Most of the vertebrae were found in articulation.
> The centra of the larger vertebrae are about 7 cm in diameter, and 4-5 cm in length
> Elements of pectoral and pelvic girdles present (damaged); many ribs and fragments of bone
> Distal elements of at least one paddle present
> One gastrolith was found in contact with a dorsal vertebra
> Some evidence of scavenging is present (bite marks / shark tooth)
> A portion of the remains were briefly colonized by oysters before burial
Since then, with some gentle reminders from Bruce Schumacher, I have come to realize the specimen does not contain sufficient diagnostic features to actually identify it as Dolichorhynchops osborni (or Trinacromerum bentonianum). The last Trinacromerum remains occur in the Fairport Chalk (Middle Turonian - See Schumacher and Everhart, 2005)... and the first identifiable Dolichorhynchops remains occur in the early Campanian (Carpenter, 1996; Everhart, 2003)... leaving a gap of over 6 million years where no species of polycotylid has ever been positively identified from the Western Interior Sea.
In 2003, I described some very fragmentary, partially digested plesiosaur remains from the lower Smoky Hill Chalk (Late Coniacian) that were "probably" Dolichorhynchops, but did not exhibit any good diagnostic features. Based on the characteristics of the vertebrae of FHSM VP-16459, I could say with some confidence that the remains were NOT from Polycotylus latipinnis Cope 1869... the first polycotylid described from the Smoky Hill Chalk. What I cannot do is distinguish FHSM VP-16459 from Trinacromerum on the basis of the remaining vertebrae or limb elements. Most likely it is Dolichorhynchops, possibly an earlier form, but for now I have to identify it as something that looks like (cf.) Dolichorhynchops. Additional specimens would be helpful as would a better definition of the post-cranial differences between the various species. So many fossils, so little time....
Here's a photographic summary of what we have recovered and prepared to date for FHSM VP-16459:
|LEFT: Drawing adapted from original field sketch of the specimen
by Ramo Decker.
RIGHT: Dorsal vertebrae and ribs in left lateral view.
|LEFT: Three articulated, anteriormost dorsal vertebrae (left) and
the last cervical vertebra (right), left ventrolateral view.
RIGHT: Two views of two dorsal vertebrae that were preserved in their natural articulation.
|LEFT: Three views of a single dorsal vertebra.
RIGHT: Three dorsal vertebrae in posterior view.
|LEFT: A complete dorsal vertebra with fused ribs. This apparently
indicates that the plesiosaur was relatively old at death. Possibly a pathology?
RIGHT: A single dorsal vertebrae with a rib fragment lying across the dorsal process.
|LEFT: One of the ilia that attach the pelvic girdle to the
RIGHT: Distal elements of at least one of the paddles.
|LEFT: One of the dorsal vertebra of VP-16459with a gastrolith
pressed against the dorsal process.
RIGHT: A close up of the gastrolith lying next to the bone.
FAR RIGHT: A close-up of the gastrolith. This is the only one found to date in association with this specimen.
|LEFT: Serrated bite marks on one of the dorsal spines of the
RIGHT: A single tooth of Squalicorax falcatus found in association with the remains.
|LEFT: A map of the Western Interior Sea during Early Coniacian
time (87-89 mya) showing the approximate locations of (1) the type specimen of Dolichorhynchops
osborni (Logan County); (2) the unidentified remains of polycotylid plesiosaurs from
Gove County and; (3) FHSM VP-16459 in the Fort Hays Limestone of Jewell County.
RIGHT: Stratigraphic column showing the occurrence of plesiosaurs in the Fort Hays Limestone, Fairport Chalk and Greenhorn Limestone (Adapted from Schumacher and Everhart (2005).
Preliminary faunal list - Jewell County
Basal Fort Hays Limestone Codell Sandstone
(Early Coniacian ~ 89 mya) (Middle Turonian ~ 91 mya)
Elasmosaurid (Mudge, 1874) Mosasaurs (Tylosaurus sp.?)
cf. Dolichorhynchops sp. (Decker, 2005) Hadrodus sp.
Xiphactinus audax Albulidae indet.
Protosphyraena cf. perniciosa
Cretoxyrhina mantelli Cretoxyrhina mantelli
Squalicorax falcatus Squalicorax falcatus
Cretodus sp. Cretalamna appendiculata
Cardabiodon sp. Hybodus sp.
Carpenter, K. 1996. A Review of short-necked plesiosaurs from the Cretaceous of the western interior, North America. Neues Jahrbuch fuer Geologie und Palaeontologie Abhandlungen (Stuttgart) 201(2):259-287.
Cope, E. D. 1869. [Remarks on fossil reptiles, Clidastes propython, Polycotylus latipinnis, Ornithotarsus immanis.]. Proceedings of the American Philosophical Society xi p. 117. (meeting of June 18, 1869)
Cragin, F. W. 1888. Preliminary description of a new or little known saurian from the Benton of Kansas, American Geologist 2:404-407.
Everhart, M. J. 2003. First records of plesiosaur remains in the lower Smoky Hill Chalk Member (Upper Coniacian) of the Niobrara Formation in western Kansas. Kansas Academy of Science, Transactions 106(3-4):139-148.
Everhart, Michael J. 2005. Oceans of Kansas - A Natural History of the Western Interior Sea. Indiana University Press, 320 pp. ISBN: 0253345472
Everhart, M. J. 2007. Sea Monsters: Prehistoric Creatures of the Deep. National Geographic, 192 p.ISBN-13:978-1426200854
Everhart, M.J., R. Decker and P. Decker. 2006. Earliest remains of Dolichorhynchops osborni (Plesiosauria: Polycotylidae) from the basal Fort Hays Limestone, Jewell County, Kansas. Abstracts from the 138th> Annual Meeting, Kansas Academy of Science, Transactions 109(3-4):251.
Mudge, B. F. 1876. Notes on the Tertiary and Cretaceous periods of Kansas. Bulletin U.S. Geological Survey Territories (Hayden), 2(3):211-221.
O'Keefe, F. R. 2008. Cranial anatomy and taxonomy of Dolichorhynchops bonneri new combination, a polycotylid plesiosaur from the Pierre Shale of Wyoming and South Dakota. Journal of Vertebrate Paleontology 28(3): 664-676.
R.L. and Gillette, D.D. 2009. Unusual occurrence
of gastroliths in a polycotylid plesiosaur from the Upper Cretaceous Tropic Shale,
Schumacher, B. A. and M. J. Everhart. 2005. A stratigraphic and taxonomic review of plesiosaurs from the old Fort Benton Group of central Kansas: A new assessment of old records. Paludicola 5(2):33-54.
Sternberg, G. F. and M. V. Walker. 1957. Report on a plesiosaur skeleton from western Kansas. Kansas Academy of Science, Transactions, 60(1):86-87.
Williston, S. W. 1902. Restoration of Dolichorhynchops osborni, a new Cretaceous plesiosaur. Kansas University Science Bulletin, 1(9):241-244, 1 plate.
Williston, S. W. 1908. North American plesiosaurs: Trinacromerum. Journal of Geology 16:715-735. figs. 1-15.
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