Journal of Paleontology, 91(6), 2017, p. 1228–1243 Copyright © 2017, The Paleontological Society 0022-3360/17/0088-0906 doi: 10.1017/jpa.2017.64


More-complete remains of Procolpochelys charlestonensis (Oligocene, South Carolina), an occurrence of Euclastes (upper Eocene, South Carolina), and their bearing on Cenozoic pancheloniid sea turtle distribution and phylogeny


Robert E. Weems,1 and K. Mace Brown2


1Calvert Marine Museum; Solomons, MD 20688; Paleo Quest, Gainesville, VA 20155 ⟨rweems4@gmail.com⟩ 2Museum of Natural History, College of Charleston, Charleston, SC 29424 ⟨brown.mace@gmail.com⟩


Abstract.—New and more-complete material of Procolpochelys charlestonensis Weems and Sanders, 2014 provides the first detailed information on the skull, jaw, and plastron of this species, which occurs in the Oligocene Ashley and Chandler Bridge formations near Charleston, South Carolina. This material allows a much more detailed comparison of this turtle with the co-occurring pancheloniid species Ashleychelys palmeri Weems and Sanders, 2014 and Carolinochelys wilsoni Hay, 1923a, as well as with its Miocene successor Procolpochelys grandaeva (Leidy, 1851). Fused dentaries, found in the Cooper River north of Charleston, belong to the pancheloniid genus Euclastes, previously known only from the Upper Cretaceous and Paleocene. This specimen, apparently from the upper Eocene Parkers Ferry Formation, expands the temporal range of this genus and indicates that Euclastes survived in the North Atlantic basin far longer than was previously known. These new finds, combined with previous records of fossil pancheloniid sea turtles, provide an improved picture of the temporal distribution, evolutionary trends, and likely phylogeny of pancheloniids from the Late Cretaceous to the present.


Introduction


A pancheloniid sea turtle, Carolinochelys wilsoni, was first described from the Oligocene of the Charleston, South Carolina (S.C.) region by Hay (1923a, 1923b) based on a well-preserved skull and a humerus that he presumed represented the same species. Based on a great many specimens found in the Charleston region over the past forty years, Weems and Sanders (2014) recently provided a much more complete description of C. wilsoni and named two more Oligocene pancheloniid species (Ashleychelys palmeri and Procolpochelys charlestonensis). Both Carolinochelys and Ashleychelys were represented by enough material to establish most of their skeletal anatomy, but the third species (Procolpochelys charlestonensis) was largely based on a single specimen that included good carapace material, but only a scattering of other elements. Fortunately this associated material included the humerus, which shows that the humerus Hay (1923b) ascribed to Carolinochelys actually pertains to P. charlestonensis Weems and Sanders, 2014. Recently, much more complete material of P. charlestonensis has been discovered in the Charleston, S.C. region (Fig. 1) and placed in the Mace Brown Museum of Natural History at the College of Charleston. This material is described here to largely complete documentation of the axial skeleton of this turtle, which now can be compared in much greater detail to the skeletons of the other two South Carolina Oligocene pancheloniid species. A pair of fused dentaries, referable to the pancheloniid genus Euclastes, also recently came to light, which


appears to document the persistence of this turtle throughout most or all of the Eocene.


Materials and methods


Repositories and institutional abbreviations.—The material examined for this study is housed in the College of Charleston Natural History Museum (CCNHM) and in the vertebrate paleontology collections of the Charleston Museum (ChM PV). Anatomical nomenclature used in the descriptions provided herein follows Gaffney (1979), especially his fig. 9.


Systematic paleontology Class Reptilia Laurenti, 1768


Order Testudines Linnaeus, 1758 Suborder Eucryptodira Gaffney, 1975


Family Pancheloniidae Joyce, Parham, and Gauthier, 2004 Genus Procolpochelys Hay, 1908


Procolpochelys grandaeva (Leidy, 1851) Figures 2, 3, 6


Materials.—CCNHM 893, associated skull and lower jaws; CCNHM 300.1, associated carapace and plastron.


Occurrence.—These specimens were collected from the Chandler Bridge Formation (upper Oligocene, mid-Chattian) in Charleston County, South Carolina. More specific locality data


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