Rodhocetus is one of several extinct whale genera that possess land mammal characteristics, thus demonstrating the evolutionary transition from land to sea.
The first species to be discovered (Rhodocetus kasrani) exhibited such features as a large pelvis fused to the vertebrae, hind legs, and differentiated teeth. Of a recently discovered species (Rodhocetus balochistanensis), the ankle bones were recovered, further strengthening the already well-founded link to artiodactyls, and weakening the link to mesonychids.
Rodhocetus balochistanensis is in fact believed to demonstrate a direct evolutionary link to artiodactyls (modern examples of which include hippopotamuses, now believed to be the closest cousin species of the cetaceans). The structure of the ankle bones of this species, the trochlea, is double-spooled. This trait is only known in artiodactyls, as all other mammalian orders have a single-spooled trochlea. This matches studies of the genetic relations between whales and other animals. Previous fossil-based hypotheses that whales were directly descended from mesonychids have been largely overturned.
The ear bones of Rodhocetus are already very whale-like, though the swimming style is very different. Rodhocetus is more obviously aquatic than earlier known species (e.g. Ambulocetus) and had large, paddling hind feet to propel it through the water. It also had a strong tail which may have helped to act as a rudder.
ManyRodhocetus may have swum like a modern otter, but through a principal components analysis done in 2003, Philip Gingerich demonstrated that its limb proportions were closer to that of the Russian desman.
The first fossils of this species were found in Balochistan Province, Pakistan in 2001 by Philip Gingerich. Dating from about 47 million years ago, they are one of a series of recent discoveries, including the pakicetids, which have thrown considerable light on the previously mysterious evolutionary origin of whales.
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