Simon F. Mitchell, Contributor
Fossil skeleton of pezosiren portelli - the manatee that walked - on display in the Geology Museum, University of the West Indies.
JAMAICA HAS a geological history stretching back at least 140 million years. Jamaica began as a volcanic island, like the islands of the eastern Caribbean.
From 40 to 55 million years ago (during the Eocene era), volcanism gradually ceased and the island was submerged by the sea forming a series of shallow-water carbonate banks, much like the modern Bahamas. Jamaica and the Blue Mountains only began to be uplifted some 14 million years ago. The transition from volcanic island to carbonate banks represents an important geological interval for Jamaica. It is during this time that the yellow limestone was deposited and represents extensive river deltas and shallow lagoon and bay systems.
The yellow limestone is now seen as a possible source for hydrocarbons in the current oil exploration occurring off the south coast. Geologists from the University of the West Indies (UWI) have been researching these deposits for the past 50 years.
In 1990, Roger Portell of the Florida Museum of National History discovered a series of fossil manatee bones near Seven Rivers in St. James. Over the past 12 years a team from UWI (Steve Donovan (formerly of UWI), Simon Mitchell and Thomas Stemann), Howard University (Daryl Doming) and Florida Museum of Natural History (Roger Portell) has been excavating the site supported by the National Geographic Society.
The site contains a wealth of fossil vertebrate remains including lizards, turtles, crocodiles, sea cows (manatees) and a rhinoceros. The sea cow has been named pezosiren portelli and is the most complete, primitive sea cow yet discovered. It is unique to Jamaica. Pezosiren was a pig-size animal with a length of 2.1 metres; it had a short neck, a barrel-shaped trunk, a moderate-length tail and four short legs. The morphology of the skeleton of pezosiren is comparable to that of similar-sized land mammals and indicates that pezosiren was capable of supporting its body weight out of water.
Pezosiren is a distant relation of the endangered manatee that has flippers, and lives in the shallow seas around Jamaica. Other characteristics (such as details of the nasal opening and the thick ribs), however, suggest that pezosiren spent much of its time in the water.
Thus it represents a unique glimpse in the evolution of the sea cows (a missing link) when they moved from the land into the water. The skeleton is displayed in the Geology Museum at the University of the West Indies.
