Pseudemys williamsi shell

UF 11561, in left lateral view

Pseudemys williamsi

Quick Facts

Common Name: Williams’ cooter

Pseudemys williamsi is a member of the family Emydidae, which includes the pond and box turtles.

This species has been only been positively identified from two Florida localities.

Pseudemys williamsi has a smooth shell and shares several characteristics with the modern river cooter, Pseudemys concinna.

Age Range

  • Late Miocene Epoch; early Hemphillian Land Mammal Age
  • About 9 to 7 million years ago

Scientific Name and Classification

Pseudemys williamsi (Rose and Weaver, 1966)

Source of Species Name: This species was named to honor Ernest E. Williams, a professor at Harvard University who studied recent and fossil turtles.

Classification: Reptilia, Testudines, Cryptodira, Testudinoidea, Emydidae, Deirochelyinae

Alternate Scientific Name: Chrysemys williamsi

Pseudemys williamsi map

Figure 1. Map of Florida, with highlights indicating counties where fossils of this species have been found.

Overall Geographic Range

This species has been only been positively identified from the two Florida localities listed.

Florida Fossil Occurrences

Florida fossil sites with Pseudemys williamsi:


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 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.

Pseudemys williamsi, fig 2

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.

Pseudemys williamsi, fig 3

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.

Pseudemys williamsi, fig 4

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.

 If the diet and habitiat of Pseudemys williamsi resembled that of the living Pseudemys concinna, then it lived primarily in rivers and had a mixed diet of water vegetation and small aquatic animals.


  • Original Author(s): Sean M. Moran
  • Original Completion Date: December 11, 2012
  • Editor(s) Name(s): Richard C. Hulbert Jr.
  • Last Updated On: March 3, 2015
Scientific References (Click to View)


This material is based upon work supported by the National Science Foundation under Grant Number CSBR 1203222, Jonathan Bloch, Principal Investigator. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation. 

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