Fossil reptile was champion chewer

The skull is remarkably well-preserved

By BBC News Online's Helen Briggs

The skull of a small creature that walked the Earth before the dinosaurs could explain how plant-eating vertebrates came to dominate land.

The squirrel-sized reptile was equipped with a mighty jaw of teeth that enabled it to shred plants with astonishing efficiency.

Scientists believe that the ability to process high fibre plant matter was the key to early success on land.

The fossils were found on the Vyatka River, central Russia

Evidence from the fossil record shows that around the same time that the animal appeared, about 260 million years ago, there was a burst of vertebrate life on land.

The animal, Suminia, is among a group of plant-eaters on the evolutionary line to mammals.

Called Anomodonts (an-om-o-donts), they were the dominant land creatures more than 250 million years ago, long before even the dinosaurs had appeared on Earth.

The creature had large eyes, big teeth and was probably scaly.

'Superbly preserved'

The skull of Suminia was found in central Russia, about 800 kilometres (497 miles ) east of Moscow, on the Vyatka river.

If you look at living animals, the most successful in terms of plant eaters are those that chew their food quite extensively in their mouth

Robert Reisz, University of Toronto

"It is a superbly preserved skull," said Robert Reisz of the University of Toronto in Mississauga, Canada. "This is the oldest land animal in which we can see how the teeth come together and work against each other."

Suminia is unusual because it had very large teeth that occluded, or met. This is not seen in iguanas, crocodiles and most other reptilian vertebrates.

By studying the pattern of wear on the teeth, Professor Reisz and co-researcher Natalia Rybczynski of Duke University, North Carolina, US, have been able to deduce that the animal was almost exclusively a plant-eater.

High-fibre diet

Tell-tale horizontal scratches on its serrated teeth reveal that it would have been capable of chewing plant material in its mouth.

In contrast, older land-dwelling plant-eaters simply swallowed leaves whole.

"If you look at living animals, the most successful in terms of plant eaters are those that chew their food quite extensively in their mouth," Professor Reisz told BBC News Online. "It suggests to us that this is a great evolutionary innovation."

Plant-eaters dominate the Earth, even today

Even today, plant-eating animals, such as gazelles and antelopes, dominate the landscape compared with top predators like lions and tigers.

Being able to gain energy by chewing high-fibre vegetation may have been essential for warm-blooded animals.

And the rise of the herbivores would have in turn provided food for predators.

If this is the case, modern-day herbivorous mammals may owe their munching ability to the mammal-like reptile that lived 260 million years ago.

The work is published in the journal Nature.