for National Geographic News
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The fossil remains of a giant rodent that weighed an estimated 1,500 pounds (700 kilograms) is helping scientists form a clearer image of what northern South America was like some eight million years ago.
Heralded as the world's largest rodent, Phoberomys pattersoni looked more like a giant guinea pig (Cavia porcellus) than an oversized house rat (Rattus rattus) and it apparently flourished on a diet of vegetation, not scraps dropped on the kitchen floor.
"Phoberomys was most likely a herbivore, and I seriously doubt it was a pest," said Marcelo Sánchez-Villagra, a paleontologist at the University of Tübingen in Germany. "When thinking of Phoberomys, think guinea pig, not rat."
Orangel Aguilera, a zoologist with the Universidad Francisco de Miranda in Venezuela, together with a colleague, discovered the Phoberomys fossils in 1999 in the Urumaco Formation, a desert region near the northwest coast of Venezuela.
Sánchez-Villagra and Ines Horovitz, a professor of organismic biology, ecology, and evolution at the University of California, Los Angeles, together with Aguilera, performed detailed studies of the fossils beginning in 2002. The team's report was published in the September 19 issue of the journal Science.
"It's really an exciting find," said Louise Emmons, a field biologist who specializes in neotropical mammals at the Smithsonian Institution in Washington, D.C.
Filling the Void
Most fossils from South America have been recovered from the southern portion of the continent, so discoveries in the northern part fill a notorious void in the fossil record, said Horovitz.
"The remains of Phoberomys and the fauna associated with it give us clues about the members of a specific kind of ecological community in this area of South America: that of a coastal community, which was very different from what we see nowadays," she said.
Aguilera has recovered several other fossils from the ancient coastal lagoons during ongoing research partially funded by the National Geographic Society. Among the discoveries are several ancient fish species related to living fish in the Orinoco and Amazon rivers.
"These discoveries reveal the presence of a proto-Orinoquian fauna, which suggests that the fossil deposits in Urumaco are related to the old delta of the Orinoco River," said Aguilera.
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