An arm bone and a handful of vertebrae have yielded a surprising truth: The age of the dinosaur began earlier than anyone ever suspected.
A new bone analysis of fossils collected in Tanzania in the 1930s reveal that Nyasasaurus parringtoni -- a creature the size of a Labrador retriever with a five-foot-long tail -- may be the earliest dinosaur on Earth, plodding across the planet some 243 million years ago.
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, according to Sterling Nesbitt, a University of Washington postdoctoral researcher in biology and lead author of a paper published online Dec. 5 in Biology Letters.
"If the newly named Nyasasaurus parringtoni is not the earliest dinosaur, then it is the closest relative found so far," Nesbitt said.
Working with one humerus or upper arm bone and six vertebrae, Nesbitt and colleagues determined that Nyasasaurus likely stood upright, measured 7 to 10 feet in length, was as tall as 3 feet at the hip and weighed as much as 135 pounds.
Unusual looks aside, the analysis of the bones, which were kept partly in London’s Natural History Museum and partly in the South African Museum in Cape Town, prove that dinosaurs have been around for an awfully long time.
"For 150 years, people have been suggesting that there should be Middle Triassic dinosaurs, but all the evidence is ambiguous," Nesbitt said. "Some scientists used fossilized footprints, but we now know that other animals from that time have a very similar foot. Other scientists pointed to a single dinosaur-like characteristic in a single bone, but that can be misleading because some characteristics evolved in a number of reptile groups and are not a result of a shared ancestry."
The fossilized bones were collected 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 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.
"The bone tissue of Nyasasaurus is exactly what we would expect for an animal at this position on the dinosaur family tree," said co-author Sarah Werning at the University of California, Berkeley, who did the bone analysis. “The bone tissue shows that Nyasasaurus grew about as fast as other primitive dinosaurs, but not as fast as later ones."
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.
"What's really neat about this specimen is that it has a lot of history. Found in the '30s, first described in the 1950s but never published, then its name pops up but is never validated. Now 80 years later, we're putting it all together," Nesbitt said.