Chrysocetus

Chrysocetus is a genus of extinct archaeocete ceteceans belonging to the Basilosauridae that is known from the Late Eocene of the eastern United States and western Africa. Across its range two species are known, the American Chrysocetus healyorum and the African Chrysocetus fouadassii, named in 2001 and 2015 respectively. Chrysocetus was a comparably small basilosaurid, larger than Saghacetus and Tutcetus but smaller than most other members of this group. In addition to being noted for its well-preserved hip bones, Chrysocetus is unique amongst basilosaurids for possibly having only had a single set of teeth. Though the fusion of the skeleton indicate that the holotype was a juvenile or subadult, the teeth represent the adult condition, having led to the hypothesis that unlike other basilosaurids and like modern whales, Chrysocetus did not replace its teeth but rather kept a single set throughout its life.

==History and naming== The type species, Chrysocetus healyorum, is based on a single subadult specimen from the late middle or early late Eocene of Orangeburg County, South Carolina. Initially, Uhen and Gingerich list the Cross Formation as being the source of the type material, tho later studies regard this horizone as a member of the Tupelo Bay Formation. The holotype, SCSM 87.195, consists of a partial skull with lower jaws, ten teeth, and the hyoid apparatus; 21 vertebrae, some ribs and a sternum; a partial left forelimb; and partial innominates. This species was discovered by Craig and Alice Healy, for which the type species was named, and scientifically described in 2001 by Mark D. Uhen and Phillip D. Gingerich. In their study, the two paleontologists took particular note of the innominate bones, as Chrysocetus was the first dorudontine with preserved pelvic material though its phylogenetic position remains variable across studies.