A novel marine turtle (Pan-Chelonioidea: Ctenochelyidae) from the Maastrichtian Neylandville Marl Formation of north central Texas, U.S.A

Abstract The marine turtle family Ctenochelyidae was a Late Cretaceous North American radiation of Pan-Chelonioidea, broadly distributed along the coastlines of the Atlantic Coastal Plain and Mississippi Embayment. Here, we describe a large, mostly articulated carapace representing a novel species of the ctenochelyid genus Asmodochelys from the Maastrichtian Neylandville Marl Formation in north central Texas. The specimen is diagnosed as a ctenochelyid by its large cordiform carapace with a broad nuchal embayment, prominent neural keel with epineural ossifications, and costoperipheral fontanelles. It has a unique combination of characters: large size (~ 120 cm); epineurals dorsal to N1/2, N3/4, N5/6, and N7/8; robust articulation between costal 1 and peripherals 1–2; lack of postnuchal fontanelles; pronounced anterior horn-like projection of peripheral 1; weakly scalloped posterior peripherals. Maximum parsimony phylogenetic analyses were conducted in TNT v1.6, and in the resulting majority-rule consensus trees, the specimen was positioned at the base of Ctenochelyidae in an unresolved polytomy with Asmodochelys parhami and the unresolved clade of ( Peritresius ornatus + Prionochelys matutina + Ctenochelys acris + Ctenochelys stenoporus ). The Neylandville Marl lies within the faunal zone of the marine oyster Exogyra cancellata, providing a particular marine ecological context that extends from Mexico to New Jersey. The new species extends the stratigraphic range of Asmodochelys into the Maastrichtian of the Gulfian Series, and geographically further west of the Mississippi Embayment to north-central Texas. It is one of the latest surviving members of the Ctenochelyidae persisting into the Maastrichtian, a time of global climatic cooling when other major Campanian marine turtle lineages, such as protostegids and Toxochelys -like early stem-chelonioids faced extinction.