An Unexpectedly Derived Odontocete from the Ashley Formation (Upper Rupelian) of South Carolina, U.S.A.

—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 const...