WASHINGTON - A rodent the size of a buffalo? Researchers say they have found fossils for a 1,545-pound giant that thrived millions of years ago in a swampy South American forest.
"Imagine a weird guinea pig, but huge, with a long tail for balancing on its hind legs and continuously growing teeth," said Marcelo R. Sanchez-Villagra of the University of Tubingen in Germany, the first author of a study appearing this week in Science (www.sciencemag.org)
The formal name of the rodent is Phoberomys pattersoni. The last term is in honor of Bryan Patterson, a Harvard professor who led a fossil-collection expedition to Venezuela in the 1970s. Informally, the skeleton is called Goya.
Researchers found the fossils in a semidesert area of Venezuela, about 250 miles west of Caracas.
When Goya lived there, some 6-million to 8-million years ago, the area was a lush paradise for a large plant eater.
"It was forested and swampy with a big river and a lot of vegetation," Sanchez-Villagra said.
The giant rodent grazed on grasses, which he must have eaten in large amounts to support his great size. Goya had fur, a smooth head with small ears and eyes, and a large tail that enabled it to balance on two hind legs to watch for predators, Sanchez-Villagra said.
"The environment was very diverse," he said. "There were lagoons and forested areas very near the seashore and fauna from a large river," probably connected to today's Orinoco, which flows east from the Amazon.
Urumaco sits on the site of an old oilfield where a petroleum geologist in 1952 discovered a rock layer rich in fossils - especially of turtles, crocodiles and other reptiles. In 1970 zoologist Roger Wood, then a Harvard graduate student, saw the exhibits at Venezuela's Central University and enlisted the university's help in mounting an expedition with his world-renowned mentor, Harvard mammalogist Patterson.
Urumaco "had a special attraction, because it was the northern-most paleontological site in South America at the time," recalled Wood, who teaches at New Jersey's Richard Stockton College. Thus it offered a unique desert exposure in a latitude where a blanket of tropical forest makes systematic excavation unfeasible.
The expedition yielded spectacular reptile finds, including several huge crocodile species and a turtle shell 81/2 feet long - still the largest turtle ever found: "We didn't find much in the way of mammals," Wood said, but a later expedition unearthed several teeth from a very large mammal.
It wasn't until 2000 that an expedition led by Orangel Aguilera of Venezuela's Universidad Nacional Experimental Francisco de Miranda found a nearly complete Phoberomys skeleton and a partial skull. It took three years of analysis to fully describe the creature.
There were a lot of predators for it to worry about, Sanchez-Villagra said.
"We know that there were crocodiles in the same location where we found this animal," said Sanchez-Villagra. "They were some of the largest crocs ever - more than 10 meters (33 feet) long."
Goya also had to worry about a large carnivore called the marsupial cat, and huge flesh-eating birds called phorracoids, he said.
Phoberomys pattersoni lived during a time when South America was isolated from the rest of the world. The isthmus of Panama had not linked the two Americas, and the southern animals evolved independently of those on the other continents.
That changed about 3-million years ago. The shifting land masses became joined at what is now Panama and animals from the two Americas began to mix. That may have spelled the demise of Goya, although it remains a mystery exactly why the animal went extinct, Sanchez-Villagra said.
"Many animals from North America made it to South America and many from the south went north," he said. "When that happened, many of the animals from South America became extinct because of competition."
In an analysis of the Sanchez-Villagra study, R. McNeill Alexander of the University of Leeds, England, wrote in Science that the large rodent may have died out because it simply couldn't escape predators.
Alexander said most rodents are small enough to hide in the ground when threatened, but Phoberomys pattersoni was too large to burrow. As do most large animals, it would have to depend on running to escape a predator.
Sanchez-Villagra said Goya's skeleton, particularly the leg bones, suggests that it walked differently from most modern rodents, such as its close cousin the guinea pig. Mice, rats and guinea pigs scamper along in a crouched position, with legs bent at the knee and elbow.
Because of Goya's mass, however, it had to stand straight, more like a sheep than a mouse.
As a result, Alexander wrote in Science, "Seen from a distance, it would have looked much more like a buffalo than like a scaled-up guinea pig."
- Information from the Washington Post was used in this report.