Reptilia, Cryptodira, Testudines, Testudinoidea, Emydidae, Deirochelyinae
PSEUDEMYS WILLIAMSI (ROSE AND WEAVER, 1966)
Common Name: Williams’ cooter
Alternate Scientific Name: Chyrsemys williamsi
Source of Species Name: This species was named to honor Ernest E. Williams, a professor at Harvard University who studied recent and fossil turtles.
Age Range: Late Miocene (early Hemphillian), from about 9 to 7 million years ago.
Florida Fossil Occurrences:
Figure 1. Map of Florida, with black circles indicating counties where fossils of Pseudemys williamsi have been found (the circles do not indicate a specific location within the county where the fossils were found, and some counties may have two or more different locations producing this species).
Florida Fossil Sites with Pseudemys williamsi:
Alachua County—Haile 19A; McGehee Farm
Overall Geographic Range: This species has been only been positively identified from the two Florida localities listed above.
Comments: Pseudemys williamsi is a smooth-shelled fossil cooter known from the late Miocene of Florida. It was first described by Rose and
Weaver (1966) from a nearly complete shell found at the McGehee Farm site in western Alachua County, with many other partial shells and nuchals. Bourque (2013) noted
the presence of Pseudemys williamsi from one other Florida locality, Haile 19A. Webb et al. (1981) briefly mentioned the presence of Pseudemys williamsi from the
Love Site, but did not include it in their faunal list (and no definite specimens are present in the Florida Museum of Natural History collection). Becker (1985)
reported either Pseudemys williamsi or the similar species Pseudemys concinna in his faunal list of the Withlacoochee River 4A site. The preservation of
the few shell elements of Pseudemys at this site suggests they are not Miocene, but instead represent contamination of a Pleistocene or Holocene P. concinna or a
similar smooth-shelled emydid turtle. The turtle fauna from Mixson's Bone Bed in the American Museum of Natural History collection has not been completely studied. Its fauna
is very similar to that of McGehee Farm, so Pseudemys williamsi might be present here.
Pseudemys williamsi is a member of the family Emydidae, which includes the pond and box turtles. Pseudemys williamsi can be distinguished from other similar taxa based on three characteristics. Pseudemys williamsi is smooth-shelled (Fig. 2) unlike the rugose shell of other taxa such as Pseudemys caeleta, and species of Trachemys and Deirochelys. Additionally, Pseudemys williamsi has a short nuchal scute (also commonly referred to as the cervical scute) underlap (Fig. 3) and short gular scute overlap on the epiplastron (Fig. 4). Pseudemys williamsi shares these characteristics with the modern river cooter, Pseudemys concinna. However, the nuchal of Pseudemys concinna is notched and more trapezoidal in shape and the posterior peripherals are slightly notched. The short nuchal underlap and gular overlap can also be used to distinguish Pseudemys williamsi from other emydids such as Pseudemys caeleta, Pseudemys floridana, and species in the Trachemys scripta complex (Rose and Weaver, 1966). Pseudemys williamsi usually co-occurs with other emydid taxa at the localities where it is found, such as Pseudemys caeleta.
Figure 2. Holotype carapace and plastron of Pseudemys williamsi, UF 11561, in dorsal (upper left), ventral (upper right), and left lateral (bottom) views. Anterior to the top in the dorsal and ventral views. Note the un-notched, rectangular pygal and un-notched posterior peripherals, as well as the smooth shell, that can be used to distinguish this species from other co-occurring emydid species.
Figure 3. Nuchals of Pseudemys williamsi, UF 65632 (left), and Pseudemys caeleta, UF 274548 (right) from the McGehee Farm site. The ventral views on the bottom show the short nuchal underlap (outlined) diagnostic of Pseudemys williamsi in comparison with that characteristic in Pseudemys caeleta. Additionally, the nuchal of Pseudemys williamsi is notably smooth compared with the rugose texture on the dorsal side of the Pseudemys caeleta nuchal.
Figure 4. Associated right and left epiplastra and entoplastron, UF 274547, from a McGehee Farm specimen of Pseudemys williamsi in ventral (left) and dorsal (view). The line in pencil on the dorsal view show the short gular scute overlap.
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Scientific Publications and Other References Cited:
Becker, J. J. 1985. Fossil herons (Aves: Areidae) of the late Miocene and early Pliocene of Florida. Journal of Vertbrate Paleontology 5: 24-31. http://www.jstor.org/stable/10.2307/4523028
Bourque, J. R. 2012. Fossil Kinosternidae from the Oligocene and Miocene of Florida, USA. Pp. 459–475 in D. B. Brinkman, P. A. Holroyd, and J. D. Gardner (eds.), Morphology and Evolution of Turtles. Springer Science+Business Media, Dordrecht. DOI: 10.1007/978-94-007-4309-0_25.
Hulbert, R. C. 2001. Fossil Vertebrates of Florida. University Press of Florida, Gainesville.
Rose, F. L., and W.G. Weaver. 1966. Two new species of Chrysemys (=Pseudemys) from the Florida Pliocene. Tulane Studies in Geology 5: 41-48.
Webb, S. D., B. J. MacFadden, and J. A. Baskin. 1981. Geology and paleontology of the Love Bone Bed from the late Miocene of Florida. American Journal of Science 281(5): 513-544. http://ajsonline.org/content/281/5/513.short
Original Author(s): Sean M. Moran
Original Completion Date: December 11, 2012
Editor(s) Name(s): Richard C. Hulbert Jr.
Last Up-dated On: March 29, 2013
Funding to generate the content and images of this and other Fossil Species of Florida web pages partailly provided by the National Science Foundation, grant CSBR 1203222, Jonathan Bloch, Principal Investigator
Copyright © 2012-2013 by Florida Museum of Natural History, University of Florida