SCIENCE: That Buffalo-Sized Rat Could Have Much to Say

By Sanjay Suri Reprint | | Print |

Sanjay Suri

LONDON, Sep 19 2003 (IPS) - What would you think of a rat that was as big as a buffalo? Even if that was eight million years ago?

For a start, perhaps that this was a long time ago, and that it hardly matters any more. Those millions of years back you had plenty of dinosaurs around, you see them no more, and no one thinks twice about those.

So why think about this rat? Or more politely, this particular giant among the rodents?

Because the discovery of a near complete fossilised skeleton of the animal in what is now north-western Venezuela offers a rare and tantalising clue to that period. And scientists say it offers rare new insights into the whole evolutionary process.

The fossilised skeleton was discovered in a now arid region 250 miles west of Caracas in the town of Urumaco. The remains of this creature are described in the Sep. 19 issue of Science International magazine published by the American Association for the Advancement of Science (AAAS).

"This was clearly a stunning animal," Dr McNeill Alexander from the University of Leeds in Britain told media representatives in London this week. "It was seriously big, which leads to the question, how could a rodent that big be possible?"

And in that size could have lain its downfall, quite literally, because "it might have had trouble supporting its own weight," said Alexander. A study of the characteristics of this animal could reveal important aspects of food habits, the environment and adaptation in the evolutionary process, he said.

Mice crouch on very bent legs, while elephants have had a better time because they keep their legs relatively straight, he said. "The giant rodent fossil raises wonderful questions about the constraints of evolution on size."

The cause of the demise of the giant rodent is unknown. But mammals such as rodents typically escape predators by burrowing into a refuge, he said. Other mammals can escape only by running. The giant rodent could have had a problem either way. "Would large rodents generally be too slow to be successful?" Dr Alexander asked.

The discovery is also leading to new investigations about particularly large animals that came to appear in this part of the world. "This was a place of giants," said Dr Marcelo Sanchez-Villagra from the University of Tuebingen in Germany.

"This is the region that produced the largest crocodiles, and turtles two metres in length."

Curious matters, for most of us. But for scientists, these could contain serious clues.

The northern region of Venezuela holds the key to many mysteries, he says. "Yet, we have known very little about this area because regions covered with vegetation are not the best place to look for fossils. With this work, we are taking steps toward broadening our knowledge of South America as a whole."

The large rodent, that is estimated to have weighed 700 kilograms, is considered an evolutionary sibling to modern-day guinea pigs.

"Imagine a weird guinea pig, but huge, with a long tail for balancing on its hind legs, and continuously growing teeth," says Sanchez-Villagra. "It was semi-aquatic, like the capybara, and probably foraged along a riverbank."

And guinea pigs are of course just that. They are critical in experiments, and the story of the evolution of the guinea pig itself could be particularly revealing.

Researchers found the fossil in mid-May 2000, but never specifically classified it until now. It has now been identified as a close relative of the guinea pig, whose weight has come down from 700 kilograms then to about a kilogram now.

"At a stroke, this giant rodent more than doubles the size range of this remarkable family of animals, and provides fascinating new insights into life some eight million years ago," says Andrew Sugden, managing editor of Science International.

The rodents we are familiar with are small. Mice weigh about 30 grams, and rats about 300 grams. By comparison, the largest living rodent, the South American capybara, seems gigantic with an adult body mass of about 50 kilograms, about as much as a typical sheep. The new discovery shows how small the capybara is in relation to what was.

More, it could say something about the whole process of evolving and becoming.