LONDON, (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 400 kilometres west of

Caracas in the town of Urumaco. The remains of this creature are described in the

September 19 issue of Science International magazine.

"This was clearly a stunning animal," Dr McNeill Alexander from the University

of Leeds in Britain said. "It was seriously big, which leads to the question,

how could a rodent that big be possible?"

In that size could have lain its downfall, 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.

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

clues.

The large rodent, 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 just that. They are critical in experiments, and the story of

the evolution of the guinea pig itself could be particularly revealing.

The rodents we are familiar with are small. Mice weigh about 30 grams, and rats about

300. 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.