Abstract:
Simocetus rayi (new genus, new species) is based upon a skull
and mandible of a small archaic dolphin (Cetacea: Odontoceti)
from the upper Oligocene Alsea Formation of Oregon, bordering
the northeast Pacific. The species shows many primitive features
reminiscent of the archaic odontocete family Agorophiidae: the
cheek teeth appear nonpolydont, the nares and premaxillary sac
fossae lie anteriorly, the orbit and facial fossa are elevated above
the level of the rostrum, the ascending processes of premaxillae
are narrow and long, the supraorbital processes of the maxillae are
narrow, the intertemporal constriction is prominent, and the pterygoid sinus fossae are restricted to the basicranium. These features
are consistent with a basal position among the odontocetes, but
they do not justify placement in the paraphyletic- and probably
polyphyletic-grade family Agorophiidae. Simocetus rayi shows
some unusual autapomorphies (toothless premaxillae, anterior of
rostrum and mandible downtumed) that exclude it from described
taxa of odontocetes, and for this reason it is placed in a new and
currently monotypic family, Simocetidae. Broader relationships
are uncertain; some cranial features hint at affinities with Eurhinodelphinidae. For now, S. rayi is regarded as a specialized archaic
odon-tocete that lies sternward (more basal) to all extant groups of
Odontoceti (namely, Physeteroidea, Ziphiidae, Platanistoidea, and
Delphinida).
Simocetus rayi was perhaps a bottom feeder that preyed through
suction feeding on soft-bodied invertebrates. The inferred presence of nasal turbinals and a vomeronasal organ contrasts with the
situation in living odontocetes. Features of the face and basicranium point to echolocation abilities comparable to those of extant
Odontoceti. Simocetus rayi and other contemporaneous archaic
odontocetes from Oregon and Washington indicate that odontocetes were taxonomically and ecologically diverse by the late Oligocene.
