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. The Triassic period extends from about 250 million to 200 million years ago. "If the newly named Nyasasaurus parringtoni is not the earliest dinosaur, then it is the closest relative found so far," according to lead author, Sterling Nesbitt from the University of Washington.
The name “Nyasasaurus parringtoni” combines the lake name “Nyasa” with the term "saurus" meaning lizard and “parringtoni" is in honor of University of Cambridge's Rex Parrington, who collected the specimens in the 1930s.
The fossilized bones were found in Tanzania, but 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 from the Natural History Museum, London.
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).
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," said co-author Sarah Werning at the University of California, Berkeley, who did the bone analysis. "In living animals, we only see this many bone cells and blood vessels in animals that grow quickly, like some mammals or birds."
"The bone tissue of Nyasasaurus is exactly what we would expect for an animal at this position on the dinosaur family tree," she added. "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."
"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 onto the scene in the Late Triassic, a burst of diversification unseen in any other groups at that time."
About 252 million years ago, up to 96% of all marine species and 70% of terrestrial vertebrate species became extinct, marking the end of the Permian and the start of the Triassic Period. It now appears that dinosaurs were just part of a large diversification of land animals (including crocodiles) which occurred after this so called ‘Great Dying’ extinction event.
The full paper is free to read for the next seven days in Biology Letters.