A small flat-shelled musk turtle from the Late Miocene of Florida and new Pleistocene records of Sternotherus (Kinosternidae)

The Montbrook Fossil Site in Levy County, Florida, is a Late Miocene (6.0–5.6 Ma) fluvial deposit with a diverse turtle assemblage that includes exceptionally well-preserved musk turtles, genus Sternotherus. Sternotherus pugnatus n. sp. is described from eight partial to nearly complete shells, jaws, a maxilla, and hundreds of isolated postcranial bones. It is a small species with a low, narrow, and smooth carapace that is flat dorsomedially and acarinate except for along the posterior midline, lacks a lateral crest along the bridge peripherals, and has highly reduced to absent axillary and inguinal scutes. A cladistic analysis places S. pugnatus and its sister taxon Sternotherus bonevalleyensis within crown group Sternotherus and sister to the extant species Sternotherus peltifer and Sternotherus depressus. Many of the fossil shells exhibit healed injuries from microbial infections and predation attempts, including pockmarks, parallel scrapes, split carapaces, a broken plastral buttress, and punctures with embedded fish tooth tips, documenting previously unknown predator-prey interactions in early Sternotherus. Early Pleistocene fossils of Sternotherus that immediately post-date Pliocene sea level inundation of Peninsular Florida are also discussed and figured, as are Middle to Late Pleistocene musk turtle fossils including Sternotherus odoratus (dwarf and large forms) and Sternotherus minor. ZooBank Nomenclatural Act—https://zoobank.org/urn:lsid:zoobank.org:act:1D0F91CC-716D-4F0C-8994-D32341EED644