Simocetus, Xenorophus, Kogia, Physeter and Livyatan (Leviathan)

Simocetus rayi (Fordyce 2002) nests basal to extant odontocetes in the LRT with laterally oriented teeth. Distinct from related taxa, Simocetus had a domed head for the naris along with a toothless premaxilla. The coronoid process was absent.

Xenorophus sloanii (Leidy 1869, Boessenecker and Geisler 2023, Late Oligocene) nests with the much larger Livyatan in the LRT, not with dolphins and not prior to Simocetus, despite its dolphin-like size.

Livyatan melvillei (originally Leviathan melvillei Lambert et al. 2010; 3m skull length; late Miocene) is a transitonal taxon linking archaeocetes, like Aetiocetus, with odontocetes like Physeter and Tursiops. Giant teeth line short, wide jaws.

Physeter macrocephalus (sperm whale; extant; Linneaus 1758; 4m skull length, 16m total length) is the largest member of the Odontoceti, or toothed whale and the largest tenrec. All teeth are missing from the premaxilla and maxilla. The dished-out rostrum and forehead house a large oil-filled organ used in echolocation. Odontoceti have five fingers.

Kogia sima (Owen 1866, up to 2.7m long) is the extant dwarf sperm whale. The small size, lack of upper teeth and short rostum built for sucking are three indicators of neotony.

Boessenecker RW and Geisler JH 2023. New Skeletons of the Ancient Dolphin Xenorophus sloanii and Xenorophus simplicidens sp. nov. (Mammalia, Cetacea) from the Oligocene of South Carolina and the Ontogeny, Functional Anatomy, Asymmetry, Pathology, and Evolution of the Earliest Odontoceti. Diversity 2023, 15, 1154.
https:// doi.org/10.3390/d15111154

Fordyce RE 2002. Simocetus rayi (Odontoceti: Simocetidae, New Family): A bizarre new archaic Oligocene dolphin from the Eastern North Pacific. Pp. 185–222 In Emry, RJ (ed), Cenozoic Mammals of Land and Sea: Tributes to the career of Clayton E. Ray. Smithsonian Contributions to Paleobiology 93.

Leidy J. 1869. The extinct mammalian fauna of Dakota and Nebraska, including an account of some allied forms from other localities, together with a synopsis of the mammalian remains of North America. J. Acad. Nat. Sci. Phila. Second Ser. 1869, 7, 8–472.

Linnaeus C 1758. Systema naturæ per regna tria naturæ, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio decima, reformata.'

Lambert O et al. (6 co-authors) 2010. The giant bite of a new raptorial sperm whale from the Miocene epoch of Peru. Nature 466:105–108.

Owen R 1866. On some Indian Cetacea collected by Walter Elliot, Esq. Transactions of the Zoological Society of London. 6 (1): 17–47.

wiki/Simocetus
wiki/Dwarf_sperm_whale
wiki/Physeter
wiki/Livyatan (Leviathan)
wiki/Xenorophus