Paleogene dermochelyid species richness far exceeded that of today. Leatherback sea
turtles were most species rich in the Paleogene, but their richness declined sharply
during the Neogene with only one species existing today, Dermochelys coriacea. We
describe the fossil remains of three leatherback genera (Natemys, Psephophorus, and
Egvptemys) from the upper Oligocene Chandler Bridge Formation and two (Natent vs and
Psephophorus) from the lower Oligocene Ashley Formation of South Carolina, USA. The
fossils consist of isolated and some associated carapacial ossicles. Several ossicles
are referred to Natemys sp. because their scalloped edges are indicative of the campacial
sunflower pattern specific to this genus. Additionally, two Natemys morphotypes (siatemys
sp. 1 and 2) are distinguished based on differences in ossicle thickness and internal
structure. We refer two ossicles to cf. Psephophorus sp. because of their internal
diploic structure and because one has a dorsal radial pattern while the other has
a prominent ridge that exhibits strong visceral concavity. Finally, we refer one ossicle
to cf. Egyptemys sp. because it has a shallow keel that shows little expression on
the visceral surface, although we also acknowledge the ossicle's similarity to some
ridged ossicles of the genus Psephophorus. These ossicles represent the first multispecies
assemblage of leatherback fossils reported worldwide. Furthermore, the specimens fill
both temporal and geographic gaps for extinct leatherback genera and represent the
first formally described dermochelyids from South Carolina and the Oligocene of the
Atlantic Coastal Plain.
