Antaecetus

Antaecetus is an extinct genus of pachycetine basilosaurid from the middle Eocene Aridal Formation of Morocco as well as the Fayum, Egypt. Antaecetus, although known from fewer remains in total, is markedly more complete than the closely related Pachycetus, with one specimen preserving large parts of the vertebral column up to the lumbar vertebrae and a well preserved skull. Based on these remains Antaecetus appears to have been smaller than Pachycetus, with a proportionally smaller head and much more gracile teeth. Both genera however share a highly osteosclerotic and pachyostotic skeleton, greatly increasing their weight and possibly serving as additional ballast. In turn the elongation and thickening of the vertebrae severely impacts the animals movement, most likely causing it to have been much slower and far less mobile than other archaeocetes. It has been proposed that Antaecetus was a slow moving inhabitant of shallow coastal waters, where it would ambush fish and marine molluscs. Only a single species of Antaecetus is known, Antaecetus aithai, which was originally described as a species of Pachycetus.

History and naming

Initially thought to represent a species of Platyosphys (now Pachycetus), Antaecetus was described in 2015 based on fossils from the Aridal Formation of the Gueran depression, southwestern Morocco. The fossil material, consisting of a partial skull (later thought to have been that of Eocetus), a tympanic bulla and various vertebrae was recovered in 2014 along with remains of various other basal whales, leading to the recognition of the Gueran depression as an important assemblage for research on early cetaceans. Several years after this initial paper was published a second publication was released, dealing in part with the taxonomy of Platyosphys in an attempt to clarify its status.