The first complete fossil of fierce prehistoric predator known as a gorgon has been found in South Africa.

Palaeontologists from the South African Museum and the University of Washington in the USA have unearthed what appears to be the first complete fossil of a gorgonopsid, a ferocious predator with both reptilian and mammalian features. It became extinct 250 million years ago.

During a search on the mile-high plateau in South Africa's Karoo region Roger Smith, the museum's curator of geology, found a small bone fragment jutting from a rock. The rock was in a sedimentary layer representing the geological boundary between the Permian and Triassic periods.

The fossilised bone was part of an almost complete skeleton of the mysterious pre-dinosaur also known as a gorgon. Skulls are the most common gorgon fossil discovery. But torsos are rare, probably because they were scattered by scavengers after the animal's death.

Scientists rate the discovery as highly important and it is the second significant find announced in recent days, following the revelation of a near complete skeleton of a three million year old ape-man.

The ferocious predators were up to 3 metres long

Despite more than 150 years of collecting in the Karoo, one of the richest fossil beds on Earth, this is the first complete gorgon skeleton found.

The South African Museum's collection contains more than 12,000 skeletons from the Karoo, a desert region, and includes several hundred partial gorgon specimens. Gorgon fossils have also been found in China and Russia, but again none are complete.

The discovery will allow for the first time insights into the anatomy of a gorgon's torso and limbs, and it should resolve a long debate about whether the creatures held their legs beneath them like mammals or splayed from the body like reptiles.

Gorgonopsids were the largest predators of the late Palaeozoic, the era just before dinosaurs. They grew as large as 10 feet (three metres) long and were among the most ferocious predators ever.

Their heads appeared dog-like, with large sabre-tooth upper canine teeth up to 4 inches long. But despite their somewhat mammalian appearance, their eyes were set at the sides of the head like those of a lizard, and the body was probably covered with scales rather than hair.