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

ABSTRACT-A new species of protocetid archaeocete. Eocetus wardii n. sp., is named based on material from the late Lutetian (middle Eocene, 43-44 Ma) Comfort Member of the Castle Hayne Formation, North Carolina. This material includes portions of the skull, thoracic, lumbar and caudal vertebrae, ribs, and the right innominate. The innominate (pelvis exclusive of the sacral vertebrae) has some characters in common with the innominata of other protocetids, including sufficient size to support a weight-bearing hind limb. This suggests that Eocetus wardii was capable of both terrestrial and aquatic locomotion. The innominate also includes some features in common with basilosaurid archaeocetes including a shift in the relative positions of the pubis and obturator foramen. In addition, the bone histology of Eocetus is found to be very different from that of other archaeocetes and sirenians (sea cows and dugongs). The ribs and vertebrae are composed of a central area of trabecular bone enveloped by layers of dense cortical bone. Eocetus has previously only been known from a few specimens from Gebel Mokattam near Cairo, Egypt. This identification makes Eocetus the only protocetid archaeocete genus known from both sides of the Atlantic Ocean.

INTRODUCTION

EOCETUS SCHWEINFURTHI was first described around the turn of the century, but no more new information about Eocetus has been discovered until now. It was originally called Mesocetus schweinfurthi by Fraas (1904a), but was almost immediately renamed Eocetus schweinfurthi (Fraas, 1904b), since the generic name Mesocetus had already been used for a different whale (Mesocetus Van Beneden, 1880, Mysticeti). The holotype specimen of E. schweinfurthi is a poorly preserved skull, including some teeth, that was recovered from Gebel Mokattam near Cairo, Egypt.

When Fraas (1904a) described the holotype specimen of Eocetus schweinfurthi, he also referred to it some odd vertebrae from Egypt that had been described earlier by Stromer (1903) as Zeuglodon macrospondylus. Since the holotype specimen of E. schweinfurthi does not include vertebrae, the referral of these lumbar vertebrae has remained questionable. Later, Stromer (1908) referred two additional lumbar vertebrae from Egypt to E. schweinfurthi based on comparison with the original vertebrae of Z. macrospondylus (E. schweinfurthi).

Additional specimens belonging to a new species of Eocetus, Eocetus wardii n. sp., include cranial material, ribs, vertebrae, and an innominate, and have been recognized in the collections of the United States National Museum of Natural History. Surprisingly, these specimens were not recovered from Gebel Mokattam, Egypt, but from the Comfort Member of the Castle Hayne Formation in North Carolina. Protocetid archaeocetes such as E. wardii have only recently been described from North America (Hulbert and Petkewich, 1991; Hulbert et al., 1998; Albright, 1996; Geisler and Sanders, 1996; Uhen, 1996, 1998) based on more than isolated individual bones (Kellogg, 1936). A list of all North American protocetids that have been described in papers and in abstracts is included in Table 1, with distribution information and a brief list of material known from each taxon.

The new material of Eocetus wardii is described in detail herein and compared with the holotype of Eocetus schweinfurthi and specimens previously referred to E. schweinfurthi. The innominate of E. wardii in particular is compared to the innominata of other protocetids and basilosaurids. In addition, the histology of Eocetus bone is briefly examined and compared to that of other archaeocetes and sirenians. Lastly, the phylogenetic position of Eocetus is discussed in light of the anatomical and histological data presented.

The specimens discussed here are located at the British Museum of Natural History, London (BMNH), Department of Geology Museum, University of Ibadan, Nigeria (GMUI), Geological Survey of Pakistan-University of Michigan Museum of Paleontology Collection, Islamabad (GSP-UM), Georgia Southern Museum, Statesboro (GSM), Naturmuseum Senckenberg, Frankfurt am Main (NSFM), Staatliches Museum fur Naturkunde, Stuttgart (SMNS), and the United States National Museum of Natural History, Washington DC (USNM).

SYSTEMATIC PALEONTOLOGY

Order CETACEA Brisson, 1762

Suborder ARCHAEOCETI Flower, 1883

Family PROTOCETIDAE Stromer, 1908

Type genus.-Protocetus Fraas, 1904.

Diagnosis-Thewissen et al. (1996) characterized members of the family Protocetidae as having a supraorbital shield, greatly enlarged mandibular foramina, a reduced nasopharyngeal duct (compared to Ambulocetus), and reduced hind limbs. All nonbasilosaurid archaeocetes, including protocetids, are characterized as retaining M^sup 3^, lacking well-developed accessory denticles on the cheek teeth, and having primitively oriented innominata that lack a greatly elongated pubis. The family Protocetidae is most likely paraphyletic, giving rise to the Basilosauridae (Thewissen et al., 1996; see below).

Included subfamilies.-Protocetinae Stromer, 1908; Indocetinae Gingerich et al., 1993.