Ancient tail ... an artist's impression of Nyasasaurus parringtoni, either the earliest dinosaur or the closest dinosaur relative yet discovered.
A creature no bigger than a labrador with a metre-long tail that roamed the Earth more than 240 million years ago may have been the world's first dinosaur.
Paleontologists have analysed the bones of what they believe to be the oldest species of dinosaur, named Nyasasaurus parringtoni, which lived between 10 and 15 million years earlier than the oldest known dinosaurs.
"If Nyasasaurus parringtoni is not the earliest dinosaur, then it is the closest relative found so far," said Sterling Nesbitt, a University of Washington researcher and the study's lead author.
From six vertebrae and a single upper arm bone, all excavated in Tanzania in the 1930s, a team of British and American researchers were able to reconstruct some of the nyasasaurus's features: it weighed between 20 and 60 kilograms, stood upright at about a metre tall and had fast-growing bones, typical of early dinosaurs.
When nyasasaurus lived - a period known as the middle Triassic - the world's continents were joined in a giant landmass called Pangaea.
Tanzania was part of Africa which was joined to South America, Antarctica and Australia as the southern section of the supercontinent.
"The new findings place the early evolution of dinosaurs and dinosaur-like reptiles firmly in the southern continents," said Paul Barrett, a study co-author from the National History Museum, London.
The researchers, who published their findings in the Royal Society's journal Biology Letters, found the species was more closely related to birds than crocodilians.
The creature also displayed a number of characteristics common in early dinosaurs, such as a large crest on its upper arm bone to anchor its arm muscles.
Sarah Werning from the University of California, Berkeley, who conducted the bone analysis, said the nyasasaurus's bone tissue was an example of a transitional fossil: the bone showed the species grew as fast as other primitive dinosaurs, but not as fast as later ones.
Dr Nesbitt said the nyasasaurus and its age had important implications, regardless of whether it was a dinosaur or a close relative.
"It establishes that dinosaurs likely evolved earlier than previously expected and refutes the idea that dinosaur diversity burst onto the scene in the late Triassic."
Instead, the researchers believe dinosaurs diversified from a group called archosaurs, which were the dominant creatures living during the Triassic period, 250 million to 200 million years ago.
Nyasasaurus parringtoni is named after Lake Nyasa, also known as Lake Malawi, one of the great rift lakes of Africa which is near to the excavation site.
Correction: An earlier version of this story said archaeologists had examined the dinosaur's bones. They are, in fact, paleontologists.