Dinosaur ancestor

Print edition : December 28, 2012

The upper arm bone of Nyasasaurus parringtoni next to a cross section of the bone. The many colours indicate that the bone fibres are disorganised, much like those of early dinosaurs.-

RESEARCHERS have discovered what may be the earliest dinosaur, a creature the size of a Labrador retriever but with a five-foot-long tail, which walked the earth about 10 million years before Eoraptor and Herrerasaurus. The findings mean that the dinosaur lineage appeared 10-15 million years earlier than fossils previously showed, originating in the Middle Triassic.

If Nyasasaurus parringtoni, as the creature has been named, is not the earliest dinosaur, then it is the closest relative found so far, according to Sterling Nesbitt of the University of Washington, the lead author of a paper published in Biology Letters. For 150 years, people have been suggesting that there should be Middle Triassic dinosaurs, but all the evidence is ambiguous, he said. Parringtoni is in honour of the University of Cambridges Rex Parrington, who collected the specimens in the 1930s. The researchers had one humerusor upper arm boneand six vertebrae to work with. They determined that the animal likely stood upright, measured two to three metres in length, was as tall as one metre at the hip and may have weighed 20-60 kilograms.

The bone tissue of Nyasasaurus is exactly what we would expect for an animal at this position on the dinosaur family tree, says Sarah Werning, a co-author from the University of California, Berkeley. Its 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 the later ones, she added.

The bones were collected in south-west Tanzania in the 1930s from the Manda beds, which preserve fossils of many animals from the Triassic period. But it may not be correct to say that dinosaurs originated in that country. When Nyasasaurus lived, the worlds continents were joined in the landmass called Pangaea. Tanzania would have been part of southern Pangaea, which included Africa, South America, Antarctica and Australia.

The late palaeontologist Alan Charig, included as a co-author, described and named the specimen in the 1950s but never documented or published it in a way that was formally recognised. Nyasasaurus and its age have important implications regardless of whether this taxon is a dinosaur or the closest relatives of dinosaurs, Nesbitt said. It establishes that dinosaurs likely evolved earlier than previously expected and refutes the idea that dinosaur diversity burst on to the scene in the late Triassic, a burst of diversification unseen in any other groups at that time.

It now appears that dinosaurs were just part of a large diversification of archosaurs.

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