Web edition: December 5, 2012
Print edition: January 26, 2013; Vol.183 #2 (p. 15)
What may be the most ancient dinosaur ever found — or at least a very close relative to the oldest currently known examples — could push the appearance of the awesome beasts back to 243 million years ago.
Paleontologist Rex Parrington of the University of Cambridge in England discovered the fossil in the early 1930s, preserved in a rock formation known as the Manda Beds in Tanzania’s Ruhuhu Valley. Now, a team of scientists has taken a fresh look at Nyasasaurus parringtoni. It lived during the Anisian age of the Middle Triassic period, about 10 million to 15 million years earlier than the oldest confirmed dinosaurs. The finding suggests dinosaurs evolved and diversified over a longer time frame than scientists thought, the team reports online December 4 in Biology Letters.
So far only fragments of the creature’s backbone and upper arm bone have been found, but these bear telltale features of dinosaurs, such as rapid bone growth. More fragments are needed to determine whether the fossil is in fact the oldest dinosaur or a member of the nearest sister group.
At 2 to 3 meters long and no more than 1 meter tall, Nyasasaurus was hardly a king of the beasts. It would have been slightly larger than a golden retriever but with a very long tail, says Sterling Nesbitt, a paleontologist at the University of Washington in Seattle. Nesbitt and colleagues estimate that the creature weighed about 20 to 60 kilograms.
The team examined the fossil’s structure and microscopic anatomy and then compared it with members of known animal family trees. Computer analyses showed that Nyasasaurus was either part of the dinosaur lineage or an as-yet-unknown group that’s even closer than dinosaurs’ nearest currently known relatives, silesaurids.
“In this case, there’s just not enough evidence to decide which of these two family trees it is,” says paleontologist Stephen Brusatte of the American Museum of Natural History in New York City, who was not involved with the study. “The only way to really figure out what the specimen is is to find more material,” he says.
Regardless of whether Nyasasaurus was a true dinosaur, the finding helps fill in a gap in the fossil record between dinosaurs and the branch that led to them, says paleontologist Randall Irmis of the University of Utah in Salt Lake City.
The earliest confirmed dinosaur fossils are from Argentina, and Nyasasaurus lends further support to the notion that dinosaurs arose in the southern part of the supercontinent Pangaea.
After Parrington discovered the fossil, his doctoral student Alan Charig studied the specimen for 50 years, but never published his work. With their new study, Nesbitt and colleagues have finally brought Nyasasaurus out of obscurity.
As new finds push the dinosaur record back further and further, it gets closer to the end-Permian mass extinction, which wiped out up to three-quarters of terrestrial species 252 million years ago. “It appears dinosaurs arose in the shadow of the greatest extinction of all time,” Nesbitt says.
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