Scientists believe that a set of fossilised bones, which has been kept for more than half a century in the Natural History Museum in London, belongs to the earliest-known dinosaur.
They say the fossils, which were first unearthed in the 1930s in Tanzania, are those of a creature the size of a Labrador retriever, but with a five foot-long tail, that walked the Earth about 10 million years before more familiar dinosaurs like the small, swift-footed Eoraptor and Herrerasaurus.
The findings mean that the dinosaur lineage appeared 10 million to 15 million years earlier than fossils previously showed, originating in the Middle Triassic rather than in the Late Triassic period.
"If the newly named Nyasasaurus parringtoni is not the earliest dinosaur, then it is the closest relative found so far," according to Sterling Nesbitt, a University of Washington postdoctoral researcher in biology and lead author of the study.
The researchers had one humerus - or upper arm bone - and six vertebrae to work with. They determined that the animal likely stood upright, measured 7 to 10 feet in length (2 to 3 meters), was as tall as 3 feet at the hip (1 meter) and may have weighed between 45 and 135 pounds (20 to 60 kilograms).
Though the fossilized bones were collected from Tanzania, it may not be correct to say dinosaurs originated in that country. When Nyasasaurus parringtoni lived, the world's continents were joined in the landmass called Pangaea. Tanzania would have been part of Southern Pangaea that included Africa, South America, Antarctica and Australia.
"The new findings place the early evolution of dinosaurs and dinosaur-like reptiles firmly in the southern continents," said co-author Paul Barrett at the Natural History Museum, London.
The bones of the new animal reveal a number of characteristics common to early dinosaurs and their close relatives. For example, the bone tissues in the upper arm bone appear as if they are woven haphazardly and not laid down in an organized way. This indicates rapid growth, a common feature of dinosaurs and their close relatives.
"We can tell from the bone tissues that Nyasasaurus had a lot of bone cells and blood vessels. In living animals, we only see this many bone cells and blood vessels in animals that grow quickly, like some mammals or birds," said co-author Sarah Werning at the University of California, Berkeley, who did the bone analysis.
"The bone tissue of Nyasasaurus is exactly what we would expect for an animal at this position on the dinosaur family tree. It's a very good example of a transitional fossil; the bone tissue shows that Nyasasaurus grew about as fast as other primitive dinosaurs, but not as fast as later ones," she added.
Another example is the upper arm bone's distinctively enlarged crest, needed to anchor the upper arm muscles. The feature, known as an elongated deltopectoral crest, is also common to all early dinosaurs.
"Nyasasaurus and its age have important implications regardless of whether this taxon is a dinosaur or the closest relatives of dinosaurs. 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, a burst of diversification unseen in any other groups at that time," Nesbitt said.
It now appears that dinosaurs were just part of a large diversification of archosaurs. Archosaurs were among the dominant land animals during the Triassic period 250 million to 200 million years ago and include dinosaurs, crocodiles and their kin.
"Dinosaurs are just part of this archosaur diversification, an explosion of new forms soon after the Permian extinction," Nesbitt said.
The paper describing the discovery has been published online in Biology Letters, a journal of the United Kingdom's Royal Society. (ANI)