Multispecies leatherback assemblage from the Chandler Bridge and Ashley formations (Oligocene) of South Carolina, USA

Abstract

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 Egyptemys) from the upper Oligocene Chandler Bridge Formation and two (Natemys 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 carapacial sunflower pattern specific to this genus. Additionally, two Natemys morphotypes (Natemys sp. 1 and 2) are distinguished based on differences in ossicle thickness and internal structure. We refer two ossicles to cf. Psephophorus 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 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.

New Skeletons of the Ancient Dolphin Xenorophus sloanii and Xenorophus simplicidens sp. nov. (Mammalia, Cetacea) from the Oligocene of South Carolina and the Ontogeny, Functional Anatomy, Asymmetry, Pathology, and Evolution of the Earliest Odontoceti

“…The Ashley Formation preserves calcareous marine invertebrates including the gastropod Epitonium sp., the oyster Cubitostrea sp., and the barnacle Concavus sp., though little formal study of the marine invertebrate assemblage has been published [58]. Fossil vertebrates from the Ashley Formation include sharks [59], bony fish [60], sea turtles [55,[61][62][63], sea birds (Boessenecker, pers. obs.…”

A megatoothed shark (Carcharocles angustidens) nursery in the Oligocene Charleston Embayment, South Carolina, USA

“…At the McKewn subdivision locality, the basal bonebed is rich in large, brown, irregularly-shaped nodules, and there is a second bonebed 70 cm higher that is less richly fossiliferous but dominated by tan to light gray phosphate nodules 1-3 cm in diameter. A more detailed description of the stratigraphy at this Fallon and Boessenecker (2020). locality is provided by McCuen et al (2020).…”