Dorudon

### location

ancient Tethys Sea, which used to connect the Mediterranean Sea and the Indian Ocean.

***Dorudon*** ("spear-tooth") is a genus of extinct basilosaurid ancient whales that lived alongside *Basilosaurus* 40.4 to 33.9 million years ago in the Eocene. It was a small whale, with *D. atrox* measuring 5 metres (16 ft) long and weighing 1–2.2 metric tons (1.1–2.4 short tons). *Dorudon* lived in warm seas around the world and fed on small fish and mollusks. Fossils have been found along the former shorelines of the Tethys Sea in present-day Egypt and Pakistan, as well as in the United States, New Zealand, and Western Sahara.

Gibbes 1845 described *Dorudon serratus* based on a fragmentary maxilla and a few teeth found in South Carolina. He concluded that the teeth must have belonged to a mammal since they were two-rooted, that they must have been teeth from a juvenile since they were hollow, and also noted their similarity to the teeth then described for *Zeuglodon* (*Basilosaurus*). When exploring the type locality, Gibbes discovered a lower jaw and twelve caudal vertebrae, which he felt obliged to assign to *Zeuglodon* together with his original material. Gibbes concluded that *Dorudon* were juvenile *Zeuglodon* and consequently withdrew his new genus. He did however allow Louis Agassiz at Harvard to examine his specimens, and the Swiss professor replied that these were neither teeth of a juvenile nor those of *Zeuglodon*, but of a separate genus just as Gibbes had first proposed.

Andrews 1906 described *Prozeuglodon atrox* (="Proto-*Basilosaurus*") based on a nearly complete skull, a dentary, and three associated vertebrae presented to him by the Geological Museum of Cairo. Kellogg 1936, however, realized that Andrews' specimen was a juvenile, and, he assumed, the same species as *Zeuglodon isis*, described by Andrews 1906. Kellogg also realized that the generic name *Zeuglodon* was invalid and therefore recombined it *Prozeuglodon isis*. Since then many specimens have been referred to *Prozeuglodon atrox*, including virtually every part of the skeleton, and it has become obvious that it is a separate genus, not a juvenile "Proto-*Zeuglodon*". Kellogg placed several of the species of *Zeuglodon* described from Egypt in the early 20th century (including *Z. osiris*, *Z. zitteli*, *Z. elliotsmithii*, and *Z. sensitivius*) in the genus *Dorudon*. Gingerich 1992 synonymized these four species and grouped them as *Saghacetus osiris*.

The current taxonomic status of *Dorudon* is based on Uhen 2004's revision of *Dorudon* and detailed description of *D. atrox*. Before this, the taxonomy of *Dorudon* was in disarray and based on a limited set of specimens.

*D. atrox* is known from Egypt, *D. serratus* from Georgia and South Carolina in the United States. The type species *D. serratus* was, and still is, based solely on two partial maxillae with a few teeth, cranial fragments, and a dozen vertebrae with some additional material, collected but not described by Gibbes, and referred to the type species. Before Uhen 2004, *D. atrox* was based solely on Andrews holotype skull, lower jaw, and the vertebrae he referred to it, but is now the best known archaeocete species.

The two species of *Dorudon* differ from other members of Dorudontinae mainly in size: they are considerably larger than *Saghacetus* and slightly larger than *Zygorhiza*, but also differ from both these genera in dental and/or cranial morphology. The limited known material for *D. serratus* makes it difficult to compare the two species of *Dorudon*. Uhen 2004 placed *D. atrox* in the same genus as *D. serratus* because of similarities in size and morphology, but kept them as separate species because of differences in dental morphology. Even-though *D. serratus* is the type species, the description of *Dorudon* is largely based on *D. atrox* because of its completeness. The cranial morphology of *D. atrox* makes it distinct from all other archaeocetes.