New species of protocetid archaeocete whale, Eocetus Wardii (Mammalia: Cetacea) from the Middle Eocene of North Carolina

Journal of Paleontology, May 1999 by Uhen, M D

The sides of the acetabulum are very low where the dorsal portion of the obturator foramen is present, suggesting the presence of a poorly defined acetabular notch. There are two excavations within the narrow portion of the acetabulum. Neither one is clearly homologous with structures found in other acetabula, so they will just be described positionally. The more dorsal of the excavations is very large. It originates just dorsal to the center of the narrow portion and is deepest at this origin. It becomes more shallow dorsally, and it broadens to include more of the acetabular surface, taking up about 55 degrees of arc of the circular acetabulum. The other smaller excavation is just ventral and anterior to the center. It is roughly teardrop shaped, with the apex of the teardrop pointing posteriorly. The excavation deepens anteriorly.

The surface of the narrow portion of the acetabulum is similar in shape to the lunate surface of terrestrial mammals and other early cetaceans. Despite this similarity in overall shape, the "lunate surface" is probably formed differently from the lunate surfaces of other mammals. The notch in the acetabulum of other mammals is the acetabular notch, which opens from the center of the acetabulum towards the obturator foramen. In Eocetus, the notch is formed by the more dorsal excavation described above, and it opens towards a ridge on the ischium. There is a pronounced ridge on the ischium just dorsal and ventral to the more dorsal excavation in the acetabulum. This ridge runs posterodorsally, is broad near the acetabulum and the edge of the innominate, and is narrower in the middle. Posterior to the ridge, the ischium thins away from the acetabulum, forming a broad depressed area.

The area anteroventral to the acetabulum is very thick, but rapidly thins toward the anterior edge of the innominate. The ilium extends generally anteriorly from this area and the acetabulum. The ilium comes to a very thin, sharp ventral border, while the dorsal border is much thicker and more rounded. The ilium is dorsoventrally narrowest just proximal (towards the acetabulum) to the break, indicating that the broken portion of the ilium was probably dorsoventrally broader.

Etymology.-The specific epithet, wardii is given in honor of Lauck (Buck) Ward, who discovered the holotype specimen.

Type.-Holotype USNM 310633, thoracic, lumbar, and caudal vertebrae, ribs, portions of skull, and right innominate. Locality, Lanier's Pit, Maple Hill, Pender County, North Carolina. At the end of a dirt road, extending southeastward from SSR 1532, about 0.6 km southwest from the junction of SSR 1532 and NC 50, 3.5 km southeast from Maple Hill (Feldmann et al., 1998). Lanier's Pit is located at approximately 77 deg 40'30"W longitude, 34 deg 37'30"N latitude, USGS Maple Hill quadrangle, 7.5' series.

Referred material.-USNM 449548, thoracic vertebra and portions of two ribs; USNM 449549, centrum of a lumbar vertebra.

Occurrence.-All known specimens are from the Comfort Member of the Castle Hayne Formation (L. W. Ward, personal commun., 1997). The Comfort Member has been shown to be latest Lutetian (NP 16) based on both micro- and macrofossil correlations (Hazel et al., 1984), which would place it in sequence stratigraphic cycle TA 3.5 (Harris and Laws, 1997), equivalent to local Castle Hayne sequence 2 (Harris and Zullo, 1991).