The tale of the giant ‘guinea pigs’ of Venezuela ; Fossilized rodents were buffalo-size
Scientists have found fossils of what they say is the largest rodent that ever lived, a 9-foot-long, buffalo-size creature with a long tail and powerful teeth that foraged along the riverbanks of Venezuela about 8 million years ago.
Scientists said Phoberomys pattersoni probably weighed up to 1,545 pounds, about 10 times the size of today’s largest rodent, the South American capybara, and nearly 2,500 times bigger than a 10- ounce rat.
“We like to say they are like guinea pigs, to mention something that people are more likely to recognize,” said Marcelo Sanchez- Villagra, a zoologist from Germany’s University of Tubingen and a member of the Venezuelan-led team that unearthed the remains three years ago in the fabled Urumaco fossil fields east of Maracaibo.
But Sanchez-Villagra said that among rodents, a huge mammalian order that includes field mice, hamsters, squirrels, beavers, and chinchillas, Phoberomys is most closely akin to the pacarana – a rare, 33-pound foraging animal from the western reaches of the Amazon jungle.
Sanchez-Villagra said the find, reported in today’s issue of the journal Science, provided further evidence that Urumaco, today an arid desert town near the Caribbean coast hard by Venezuela’s western oilfields, was once part of a lush tropical delta fed by an ancient river that flowed north along the eastern slope of the Andes.
“The environment was very diverse,” Sanchez-Villagra said in a telephone interview. “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 Bryan 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 8 1/2feet 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. Investigators named it Phoberomys pattersoni, in honor of Patterson, who died in 1979.
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.
Phoberomys had much heavier hind legs than front legs, indicating a relative lack of speed, and large, strong teeth for grinding the grass, leaves, and other swamp vegetation that probably made up its diet.
“I wouldn’t say the find is a tremendous surprise, but it’s pretty spectacular, ” said anatomist John Fleagle of New York’s Stony Brook University. “South America has a long history of gigantic rodents, and this is the biggest yet.”
For millions of years, Fleagle explained, South America was an “island continent” where “all sorts of strange creatures developed in isolation.” Suddenly, “between 30 [million] and 25 million years ago, primates and rodents appeared out of nowhere and radiated all over the continent,” he added.
And unlike other continents, where rodents competed for food and habitat with other small, aggressive mammals, South America offered few rivals, so rodents “went berserk,” he said.
One enduring difficulty with South American paleontology, however, “is that most of what we know is based on findings in Patagonia,” the vast, windswept desert in the continent’s southern cone, said Sanchez-Villagra. “This is a major problem.”
Urumaco presented a major opportunity to expand knowledge of the continent, for the 8 million-year-old deposit was relatively close to the spot where Earth’s restless crust brought Pacific islands ashore 3 million years ago to form the land bridge that would link the two Americas.
“When it happened, there was a huge, intense exchange of fauna,” Sanchez-Villagra said. “There was a lot of extinction on both sides,” although the disappearance of Phoberomys remains a mystery: “One likely reason for extinction is climate change,” he said. “This area was forest, swampy, full of vegetation, and 8 million years later it’s a desert.”
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