Oldest Dinosaur Found?

Just when you thought dinosaurs couldn't get any older, the oldest dinosaur has been found in Africa, a new study says.

The fossils push back the dawn of the dinosaurs to around 240 million years ago—about 10 to 15 million years earlier than previously thought, scientists say.

Dubbed Nyasasaurus parringtoni, the animal is only known from an upper arm and some back bones discovered in Tanzania in the 1930s but only recently studied in detail.

Prior to the new analysis, the oldest known dinosaur fossils belonged to small, lightly built, meat-eating creatures found in South America that dated to around 230 million years ago.

(See pictures: "Oldest Dinosaur Nests Found in South Africa.")

Oldest Dinosaur Still a Mystery

Very little is known about Nyasasaurus. Based on the fossils, scientists estimate it was between 6.5 to 10 feet (2 to 3 meters) long, including its tail. But no skull bones have been found yet, so it's unclear what the animal ate or even whether it walked on two legs or four.

However, the creature does have one distinguishing characteristic linking it to dinosaurs: a bony crest that runs along its upper arm bone.

"It's called a deltopectoral crest, and it holds shoulder muscles to the upper arm bone. All dinosaurs have this elongated crest," explained study leader Sterling Nesbitt, a paleontologist at the University of Washington.

But there's not enough information to say definitively whether the creature was a true dinosaur or whether it was the closest cousin of the dinosaurs.

Whichever the case may be, the Nyasasaurus fossil shows that dinosaurs—or their very close relatives—lived alongside another group of reptiles, called the silesaurids, for several millions years before dominating Earth.

"That's important because it shows that dinosaurs were not really anything special when they first appeared ... They were probably rare and they didn't diversify as soon as they showed up," Nesbitt said.

Dinosaurs Came From the South?

The discovery of Nyasasaurus in Tanzania also supports the idea that dinosaurs originated in the southern part of the supercontinent known as Pangaea, said study team member Sarah Werning of the University of California, Berkeley.

(Related: "New T. Rex Cousin Suggests Dinosaurs Arose in South America.")

"At this time, all of southern continents"—including Africa and South America, where the previous earliest dinosaurs were found—"are all linked up," Werning said.

Hans-Dieter Sues, a paleontologist at the National Museum of Natural History in Washington, D.C., who was not involved in the study, agreed that the "bones definitely indicate the presence of a dinosaur-like reptile in the early Middle Triassic of what is now Tanzania." (Prehistoric time line.)

This is a marked shift, he noted, from the thinking among paleontologists just a few decades ago, when such an early origin for dinosaurs was "unthinkable."

"In the 1970s, the fossil record of Triassic dinosaurs was not extensive and the oldest known forms were known only from fragmentary fossils at that time," Sues said.

"People also had no clear ideas how dinosaurs were related to other groups of [reptiles]."

The oldest-dinosaur research is detailed in the current issue of the journal Biology Letters.