A capybara jaw (Rodentia, Caviidae, Hydrochoerinae) and an isolated lower tooth fragment were recovered from dredge spoils on Pelican Island in Galveston Bay, Gulf Coast of Texas. The attached matrix on the jaw and most of the dredged material is clay, indicative of the latest Pleistocene Beaumont Formation which underlies the Holocene deposits. In the latest Pleistocene (Rancholabrean) of the United States, capybaras are known from along the Gulf and Atlantic coasts in Texas, Florida, Georgia, South Carolina, and Virginia.These Rancholabrean capybaras have been assigned to three different taxa: Neochoerus pinckneyi Hay, 1923 for the largest size specimens, Hydrochoerus holmesiSimpson, 1928 for the somewhat smaller specimens, or Neochoerus aesopiLeidy, 1853, a name that had been considered invalid because it was not adequately diagnosed, if there is only one late Pleistocene species of North American capybara.
The p4 in the new Texas mandible is much smaller than the genotype of N. pinckneyi from the Aransas River in South Texas and similar in size to H. holmesi from the Pleistocene of Florida and Recent H. hydrochaeris. However cheek tooth size and occlusal pattern in Recent capybaras varies significantly with age. Hydrochoerus holmesi cannot be distinguished from N. pinckneyi. None of the late Pleistocene capybaras of South Carolina, including the type and referred specimens of N. aesopi, have any characteristics to differentiate them from H. holmesi or N. pinckneyi. We therefore assign all the Texas and South Carolina specimens to N. aesopi.