New material of North American side-necked turtles (Pleurodira: Bothremydidae)

摘要

New cranial and postcranial material of the pleurodire family Bothremydidae, subtribe Bothremydina, from the Gulf Coastal Plain of North America, clarifies the distribution of the genera Bothremys and Chedighaii. New skull material from the Campanian Tar Heel Formation of North Carolina shows the presence of both Bothremys and Chedighaii, based on a maxilla and lower jaw. Additionally, a series of otic chambers and basicrania, while providing important information on morphology, are identified as subtribe Bothremydina, genus and species indeterminate, as the basicranium alone is insufficient to distinguish Bothremys and Chedighaii. An associated skull-shell specimen belonging to the pleurodire subtribe Bothremydina from the Campanian Mooreville Chalk of Alabama, FMNH PR 247, identified in Gaffney et al. (2006) as Chedighaii barberi, is reinterpreted as belonging to the genus Bothremys. A maxilla and jugal fragment found among the material belonging to FMNH PR 247 shows that this specimen has a skull with deep pits on its triturating surface, diagnostic of the genus Bothremys, and in contrast to the flat triturating surface of Chedighaii. Because FMNH PR 247 has an associated partial skull and shell, it was the basis for placing the species "Podocnemis" barberi Schmidt, 1940, the type of which is a shell, in Chedighaii Gaffney et al., 2006. A result of this identification is that the species "Podocnemis" barberi Schmidt, 1940, cannot be assigned to a genus, as the shell morphology of Chedighaii Gaffney et al., 2006, and Bothremys Leidy, 1865, cannot be distinguished at present. A review of the shell material in the subtribe Bothremydina concludes that shells alone are inadequate to reliably distinguish alpha-level taxa in this group at present. It is likely that ALAB PV 2001.2, NCSM 23681, and YPM PU 12951, here referred to Chedighaii sp., belong to a new species of Chedighaii, distinct from Chedighaii hutchisoni, but the material is too incomplete at present to adequately diagnosis it.