For the study published today, the team of paleontologists collected marine life from contemporary near-shore environments around the Isthmus of Panama and then compared them to the fossil record from the southwestern Caribbean during the last 10 million years.

"Bivalves such as clams and mussels are common in our contemporary samples along the Pacific side of the Isthmus where there's seasonal upwelling: really cold, nutrient-rich water pumped to the surface by the trade winds from December to April," said Jeremy Jackson, professor at Scripps and Smithsonian Tropical Research Institute emeritus.

"Corals and algae are more common in the more nutrient-poor, warmer waters on the Caribbean side."

Several approaches were used to reconstruct the environmental and ecological conditions of the Caribbean as the Isthmus rose. "Changes in the body size of fossil cupuladriid bryozoans indicate the strength of upwelling; the types of fossil foraminifera in the samples tell us the depth of the water; and percent shelly material and percent mud in the sediments give us ideas about the amount of food in the water column," O'Dea said.

The team also measured which animals and plants dominated the sea floor by weighing the fossils and monitoring changes in the proportional weights of different ecological groups through time. Ken Johnson and Jon Todd of London's Natural History Museum documented exact timing of coral and snail species, showing that up to 50 percent of species went extinct between 2 and 1 million years ago.

The environment and the ecology changed as the Isthmus closed. Water temperature stabilized in the Caribbean and carbonate deposition increased considerably between 4 and 3 million years ago. At this time corals and algae began to dominate in terms of numbers. "We don't start seeing extinction rates really increasing for a
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Contact: Beth King
kingb@si.edu
202-786-2094, ext 8216
Smithsonian Tropical Research Institute
12-Mar-2007