Sat, Sep 20, 2003 page7

• Fossil of giant guinea pig found

  EVOLUTIONARY ENIGMA Scientists in South America were amazed when they unearthed the remains of a rodent that was as big as a cow and weighed 700kg

  • THE GUARDIAN
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  It was three metres long, it weighed 700kg and it grazed on the lush banks of a South American river eight million years ago.

  Phoberomys pattersoni, alias Goya the giant guinea pig, is the biggest rodent ever found, according to the journal Science yesterday.

  In May 2000 researchers began recovering the fossilized bones from a layer of shale in what is now a hot desert region of Venezuela called Urumaco, 402km west of Caracas.

  Only when they found the jaw did they realize that they had found a rodent ten times bigger than any on earth today.

  And only when they had taken a closer look at the almost complete skeleton did they realize they had a caviomorph, cousin to the modern cavy or guinea pig. The bones were found at Tio Gregorio -- and the Spanish diminutive for Gregorio is Goya.

  "Imagine a weird guinea pig, with a long tail for balancing on its hind legs and continuously growing teeth," said Marcelo Sanchez-Villagra of the University of Tubingen in Germany.

  "It was semi-aquatic, like the capybara, and probably foraged along a riverbank."

  There are around 5,000 species of mammal on the planet today. Around 2,000 of them are rodents. The smallest weighs a few grams, the largest, the capybara, a few tens of kilograms.

  The unearthing of a species at least 10 times bigger than all the rest raises huge questions about the pace and direction of evolution -- and economies of scale.

  "This really is a stunning animal," said McNeill Alexander of the University of Leeds, an expert on the mechanics of animals.

  "If you saw this animal at a distance on a misty day it would look much more like a cow or a buffalo than like a guinea pig. Supporting its weight is no problem.

  "How about feeding itself? It would not be very easy to satisfy its appetite, because it is big. It has teeth which are obviously used for grinding abrasive food -- grass."

  Like a cow, the giant guinea pig would have depended upon micro-organisms in its gut to turn grass into nourishment.

  The bigger an animal's gut, the faster the supply of energy from the fermenting grass. But also, the bigger the animal, the more it conserves energy and the less it needs to eat.

  Other rodents have not grown to this sort of size because they tend to run down boltholes to get away from predators, which is why it helps to be small. They cannot outrun their enemies in the open.

  The implication is that Phoberomys had relatively few enemies at the time.

  The Panamanian landbridge formed only three million years ago.

  Until then, South America was separated from the northern continent, and Phoberomys lived in a very different world.

  It would probably have been at home on dry land and in the water, and it lived alongside catfish, turtles with a carapace two metres long, and predators that included a giant flightless, carnivorous bird, a marsupial cat the size of a lion and crocodiles more than nine metres long.
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