The Earliest Dinosaur, or Maybe Its Closest Kin

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Mark Witton/Natural History Museum

Researchers may have discovered the earliest dinosaur yet, or at least its closest relative.

The creature, named Nyasasaurus parringtoni, was the size of a Labrador retriever but with a five-foot-long tail. It roamed the earth about 243 million years ago, 10 million years before other early dinosaurs, like Eoraptor and Herrerasaurus.

“We’re being cautious about saying it’s the earliest dinosaur,” said Sarah Werning a paleontologist at the University of California, Berkeley, and an author of the study, which appears in the journal Biology Letters. “But if it’s not, it’s the closest cousin found to dinosaurs so far.”

The fossilized bones of Nyasasaurus parringtoni were excavated in the 1930s in Tanzania and reside in the Natural History Museum of London. The bones include one humerus, or upper arm bone, and six vertebrae.

The researchers found that the fossilized bones had an abundance of bone cells and blood vessels.

“We only see that many in animals that grow really fast,” Ms. Werning said. “It was growing about as fast as other early dinosaurs.”

The upper arm bone also has an enlarged crest, to anchor upper arm muscles — another feature common in early dinosaurs.

The fossils were first described in the 1950s by the paleontologist Alan J. Charig in his doctoral dissertation.

Dr. Charig, who died in 1997, is named as a co-author of the paper.