Walking With Sea Cows, Closing the Gap
by Brian Switek
Sea cows once walked on land. Pezosiren leaves no doubt of that.
This roughly 48 million year old mammal once trod over prehistoric Jamaica, and looked akin to a hippo with the skull of a manatee. Much like Pakicetus in the history of early whales, Pezosiren embodies a critical transitional period in the evolution of manatees and dugongs, yet the place where this amphibious sea cow was found did not match what paleontologists expected.
In the big picture of mammalian evolution, sea cows are paenungulates – members of a group that also encompasses hyraxes, elephants, and extinct branches such as the double-horned Arsinoitherium and the aquatic desmostylians.
The earliest members of these lineages first appear in Africa shortly after the end-Cretaceous extinction of 66 million years ago, with the perplexing exception of the sea cows. The earliest, most archaic progenitors of today’s manatees and dugongs, such as Pezosiren, have been found in Jamaica. Anatomical and genetic evidence is clear that sea cows must have shared an African origin with the other paenungulates, but, until now, no one has picked up the fossil trail of the earliest sirenians.
Today, in PLoS One, paleontologist Julien Benoit and colleagues describe a bone from the Eocene of Tunisia that closes the geographical gap in the sea cow backstory…
(read more: National Geo)
(images: T -uncredited; BL -by TheSuperMat | Wikipedia ; BR - Benoit et al., PLoS ONE)