Pezosiren - AbsoluteAstronomy.com

Pezosiren portelli is the name given to an early sirenian represented by a Jamaican fossil skeleton, described in 2001 by Daryl Domning, a marine mammal paleontologist at Howard University

Howard University

Howard University is a federally chartered, non-profit, private, coeducational, nonsectarian, historically black university located in Washington, D.C., United States...

in Washington, DC. It is believed to have lived 50 million years ago, perhaps with a hippopotamus

Hippopotamus

The hippopotamus , or hippo, from the ancient Greek for "river horse" , is a large, mostly herbivorous mammal in sub-Saharan Africa, and one of only two extant species in the family Hippopotamidae After the elephant and rhinoceros, the hippopotamus is the third largest land mammal and the heaviest...

-like amphibious lifestyle, and is a perfect example of a transitional form between a land mammal and a sea mammal.

It had the skull and basic body shared by most modern sirenians, like manatee

Manatee

Manatees are large, fully aquatic, mostly herbivorous marine mammals sometimes known as sea cows...

s and dugong

Dugong

The dugong is a large marine mammal which, together with the manatees, is one of four living species of the order Sirenia. It is the only living representative of the once-diverse family Dugongidae; its closest modern relative, Steller's sea cow , was hunted to extinction in the 18th century...

s, but also had four normal limbs with well-developed feet and hands, still adapted for walking on land.

Discovery

In the 1990s vertebrate fossils were found in lagoon deposits at Seven Rivers in Jamaica by Daryl Domning and colleagues. The site is rich in fossils, and yielded hundreds of bones of mainly aquatic vertebrates, bats and possibly a primate. In 2001 Domning described a walking sirenian from this site as Pezosiren portelli, based on a nearly complete skeleton. It is the first known quadrupedal sirenian, and is considered a transitional form between land and sea sirenians. Pezosiren had four limbs perfectly adapted to walking instead of flippers but at the same time the typical skull, teeth and horizontal tooth replacement of the fully aquatic, ‘normal’ sirenians. Its heavy ribs, providing ballast, indicate that it was semi-aquatic, perhaps like a hippo. The Seven Rivers site is not only one of the very rare examples of a non-cave deposit in the West Indies, but also the oldest discovered so far, with an age of late Early or early Middle Eocene. The formation was attributed to the late Early or early Middle Eocene by Robinson in 1988.
The presence of this land mammal in Jamaica can be explained as evidence of an Eocene land bridge connecting North America, the Mexican Arc, the Chortis Block, the Nicaragua Rise and Jamaica. Whatever might be the origin of this sirenian, it had no further impact in the history of the Antillean mammals, because Jamaica became submerged soon after and with it any terrestrial forms. The rest of the accompanying fossil fauna consists mainly of aquatic vertebrates—fishes, crocodilians and turtles- and a rhinocerotid species (Hyrachus).

Discovery

Further reading