A MORPHOLOGICAL DESCRIPTION OF BAPTEMYS WYOMINGENSIS AND AN ANALYSIS OF ITS PHYLOGENETIC RELATIONSHIP WITHIN KINOSTERNOIDEA (TESTUDINES)

At present, Kinosternoidae includes the extant mud and musk turtles (Kinosternidae) and the Central-American river turtle, Dermatemys mawii. Kinosternids are semi-aquatic and range from southeastern Canada to southern Brazil. Dermatemys mawii is riverine and restricted to Central America. Baptemys, an Eocene turtle from North America, has historically been allied to D.mawii within Dermatemydidae, but this relationship has never been rigorously tested in a global analysis.

Molecular data and multiple morphological characters support monophyly of Kinosternoidae, but kinosternids and D. mawii are vastly different in their morphology and the relationships of Dermatemys are controversial. Dermatemys mawii is highly adapted to consuming aquatic vegetation and is thus much more similar in gestalt to some emydids than to kinosternids. Dermatemys mawii is sometimes placed among tortoises (Testudinoidea) by a number of traits pertaining to their fully ossified shell and the development of a secondary palate. Different placements of D. mawii indicate radically different historical biogeographic scenarios and sequences of character evolution. Few relevant morphological characters have been used in global analyses of turtle relationships, and several fossil taxa are known that could prove critical to resolving this debate.

Baptemys wyomingensis is the best-sampled fossil dermatemydid. A detailed description of B. wyomingensis, along with a consideration of its phylogenetic relationships, indicates additional morphological support for a close relationship with Dermatemys and a placement for D. mawii and Baptemys within Kinosternoidae.