Researchers have found the fossil remains of a dinosaur cousin that lived 243 million years ago, making it the oldest known dinosaur relative.

dinosaur-silesaur

The dinosaur cousin Asilisaurus kongwe live in Africa in the Middle Triassic period. The sail‑backed archosaur Hypselorhachisa appears in the background. ((Marlene Hill Donnelly/Field Museum))

The four-legged creature was part of a group of dinosaur-like animals called silesaurs, close relatives that fall just outside the dinosaur family tree.

The fossils of the new species, Asilisaurus kongwe, were discovered in southern Tanzania in 2007. The name, derived from Swahili and Greek, means "ancient lizard ancestor."

Finding the species was a surprise to the paleontologists, who were expecting the early relatives of dinosaurs to be two-legged carnivores.

"The crazy thing about this new dinosaur discovery is that it is so very different from what we all were expecting, especially the fact that it is herbivorous and walked on four legs," said Randall Irmis, of the University of Utah, in a statement.

The four-legged creature, described in this week's issue of Nature, stood about a metre tall at the hip and was up to three metres long.

The silesaur's triangular teeth and beak-like tip on the lower jaw suggest that they most likely ate plants or both plants and meat.

Silesaurs and dinosaurs lived together through much of the Triassic period, between about 250 million and 200 million years ago.

The fossils of at least 14 individual animals found in 2007 are more than 10 million years older than the oldest known dinosaurs, meaning that silesaurs and dinosaurs had already diverged from a common ancestor by 245 million years ago, the researchers said.

The U.S. and German team of paleontologists said their discovery could mean that other dinosaur cousins, like the flying pterosaurs and small lagerpetids, originated much earlier than previously thought.

"The research suggests that at least three times in the evolution of dinosaurs and their closest relatives, meat-eating animals evolved into animals with diets that included plants," said Irmis.

The research also suggests there are entire groups of undiscovered animals from the early period of dinosaurs and their relatives, Irmis said.

"It's very exciting because the more we learn about the Triassic period, the more we learn about the origin of the dinosaurs and other groups," he said.