?Behemotops cf. proteus (Domning, Ray and McKenna 1986, Beatty and Cockburn 2015; Oligocene, 34-23 mya) was originally described on the basis of short, deep, but largely complete (missing the retroarticular process) and immature mandible USNM 244035. Another short, deep mandible with a distinctly different architecture and preserving the retroarticular process, USNM 244033 was also also assigned to this genus. Neither of these mandible fit the skull of another specimen, Behemotops cf. proteus RBCM.EH2007.008.0001, which preserves the left half of much of the skull, but no mandible. It is so different from the holotype it needs a new genus.

Behemotops is a desmostylian, a sister to Paleoparadoxia and basal to the rorqual whales, like Eschrichtius.

In Behemotops the jaws are largely toothless and what teeth remain are short and small. Is it possible that baleen first appeared with this taxon? The rostum and presumably the mandible curved ventrally. The nares were greatly elongated and dorsal, as in whales.

A caudal vertebra associated with the RBCM skeleton was ascribed to a dolphin-sized whale, since all other desmostylians have a vestigial tail. Given the transitional nesting of Behemotops as a stem mysticete, perhaps this whale-like caudal vertebra belongs to it.

Miocaperea pulchra (Bisconti 2012; late Miocene, 7–8 Ma; 40cm skull length) was considered a Miocene ancestor of Caperea. Here it nests between Behemotops (above) and Eschrichtius, the gray whale. The post-crania in these taxa are not well known, so they could have had legs or flippers.