AN UNEXPECTEDLY DERIVED ODONTOCETE FROM THE ASHLEY FORMATION (UPPER RUPELIAN) OF SOUTH CAROLINA, USA

Fossil whale material from the Oligocene-aged marine beds underlying the region around Charleston, South Carolina, has provided an unparalleled view of post-archaeocete cetacean evolution. Both the Chattian-aged Chandler Bridge Formation and the underlying Rupelian-aged Ashley Formation have yielded dozens of specimens, many yet-to-be described, that document an explosive evolutionary radiation at this time, particularly in odontocetes, but in early mysticetes as well. Specimens include early odontocetes, such as Ashleycetus planicapitis, Xenorophus sloanii, and Agorophius pygmaeus; the earliest baleen-bearing mysticetes, such as Eomysticetus whitmorei and E. carolinensis; and even multiple species of archaeocete-like toothed mysticetes, such as the recently described Coronodon havensteini. Herein, we describe yet another species of odontocete from the Ashley Formation, but one that is surprisingly derived relative to contemporary species noted above that maintain a pronounced intertemporal constriction, with broad exposure of the parietals across the skull roof. In contrast to those taxa, Ediscetus osbornei, gen. et sp. nov., shows an unexpectedly advanced degree of 'telescoping' whereby there is no exposure of the parietals across the vertex of the skull and only minimally exposed 'parietal triangles' at the lateral margins of the nearly lost intertemporal constriction. Phylogenetic analyses of a supermatrix of morphological and molecular data place E. osbornei slightly outside the odontocete crown group, with the presence of double-rooted teeth and a deep maxillary cleft, among other features, supporting this position. The holotype also has a well-developed articular ridge on the petrosal, typically considered a platanistoid synapomorphy, indicating that this character shows more homoplasy than generally realized.