A little prehistory… In the Middle Triassic 240-some million years ago, the archosaurs diverged into the crocodilian line and the avian line—which includes birds and dinosaurs and silesaurs, a dino-like sister group.

In this week’s Nature, scientists announced a new species of silesaur, Asilisaurus kongwe, now the oldest archosaur of the avian lineage.

“It was to dinosaurs much like chimps are to humans—kind of cousins,” author Randall Irmis from the Utah Museum of Natural History told BBC News.

While dinosaurs roamed the earth for 160 million years, silesaurs existed for 45 million. But this Labrador retriever-sized animal is about 10 million years older than the oldest known dinosaur (National Geographic). Since silesaurs and dinosaurs diverged from a common ancestor, they should have existed during the same time frame. This means the diversification of the lineage leading to dinosaurs goes back a lot further in time than scientists previously thought.

“Asilisaurus is one of the most complete close dinosaur relatives found to date,” said lead author Sterling Nesbitt from the University of Texas at Austin (but a former classmate of mine from University of California, Berkeley and Columbia University). The team pieced together the 243-million-year-old creature out of bits from at least a dozen individuals found near the town of Litumba Ndyosi, Ruhuhu Basin, Tanzania in 2007. Leaf-shaped teeth within a beak-like jaw allowed it to eat fibrous leaves off primordial palms and ferns. Its name comes from asili, Swahili for ancestor and kongwe, Swahili for ancient.

“It was a weird little creature,” Irmis said (BBC). “We always thought the earliest relatives were small, bipedal, carnivorous animals. These walked on four legs and had beaks and herbivore-like teeth.”

What’s the link between primitive reptiles and dinosaurs? The balance of opinion has alternated between more reptilian ancestors, which walked on all fours, and two-legged animals that had bird-shaped bodies but couldn’t fly, according to ScienceNOW, which says, “Recently, the idea of two-legged dino ancestors had been winning out, but the new find yanks the trend back toward quadrupeds.”

“We were really surprised,” Irmis told Wired. “It shows that there’s this real ecological diversity.”

“Everyone loves dinosaurs, but this new evidence suggests that they were really only one of several large and distinct groups of animals that exploded in diversity in the Triassic,” Nesbitt told The Times.

Image: S. Nesbitt