An ancient bone bed in a remote Mongolian desert presents tantalizing clues that dinosaurs of a feather may have flocked together for the same reasons modern birds do.
“We’re starting to realize how much birds have inherited from their dinosaur ancestors,” said Gregory Funston, a paleontologist at the University of Alberta and lead author of a paper published Monday in the journal Nature.
Funston and his co-authors have drawn their conclusions from an extensive bone bed of Avimimus fossils discovered a decade ago. The bed is likely to contain the remains of dozens of individuals of the feathered, warm-blooded, beaked dinosaur.
Scientists have long known that some dinosaurs lived together in groups but the Avimimus deposit is unique for two reasons.
The first is that remains from this type of dinosaur have only been found in a group fewer than six times anywhere in the world.
The second reason is even more interesting. Normal flocks would include both adults and juveniles, but almost all the individuals found in the Mongolian bone bed were adults.
“It suggests to us this is the result of behaviour, in which the adults group to exclude young individuals,” said Funston.
It could be mating behaviour, such as when sage grouse gather in large groups of adults. It could be foraging behaviour, as seen in ostriches, which change their diet as they age. Or it could be some other reason, still unknown.
Because the fossils were disturbed by a flood some time after the original bones were deposited, scientists can’t yet surmise exactly what the Avimimus flock was up to when it was wiped out.
Bird behaviour likely provides the best explanation, suggested Funston.
“Once you get to this group of dinosaurs, birds are probably the best comparison. They’re (dinos) probably warm-blooded. They’re all feathered.”
By this time, about 70 million years ago, the earliest birds had already evolved from an ancestor they shared with Avimimus. But scientists have yet to discover a fossil bed of those first birds which holds as many individuals as the dinosaur site in Funston’s paper.
That makes that site one of the oldest examples of the sort of behaviour that modern bird-watchers still witness on a regular basis.
“It’s the furthest down the bird tree we’ve found this kind of behaviour,” Funston said.
“That’s part of why we study these dinosaurs, because they have a common ancestor with birds.
“If we can understand the better fossil record of the dinosaurs, we can better understand that common ancestor. It is really important for understanding how birds started to group together into these flocks and how all these behavioural systems evolved.”
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The site, a two-day drive from the Mongolian capital of Ulaan Baatar where everything researchers need to live and work had to be trucked in, still has much to teach. Funston said only about 12 square metres of a 100-square-metre dig have been excavated.
Further research on the bones could be productive as well. If it turns out males are prevalent, that suggests the fossil bed could be a former site for mating behaviour.
“There’s a lot left to learn, a lot more work to be done.”