EDMONTON — A rare fossil of an eating dinosaur is shedding new light on ancient ecosystems and behaviors.
“It’s one of the few things that really gives you a sense of ecology and behavior in the fossil record,” said University of Alberta paleontologist Corwin Sullivan, who describes what he and his colleagues they found in the womb of a study of 120 million years. old Microraptor Zhaoianus in a recently published paper.
Zhaoianus (pronounced zhay-OHN-us) was a crow-sized, bird-like dinosaur. All in all, but with a bony tail and a jaw full of sharp little teeth instead of a beak, it probably glided through the forests, swamps, and lakeshores of the early Cretaceous period.
“It’s a transition between dinosaurs and birds,” Sullivan said.
This particular Zhaoianus was part of a huge collection of fossils at an institute in China where Sullivan and his co-authors worked. It had never been closely examined until they took a closer look.
Inside the dinosaur’s belly was the unmistakable ankle and foot of a mammal.
“He has a well-defined heel,” Sullivan said. “And the toes: there are no more than three toe bones in each digit, which matches the condition in mammals but not in reptiles.”
It’s rare to find an intact dinosaur, Sullivan said, and even rarer to find a small, intact dinosaur.
“There is a fierce bias against any small, delicate animal that is preserved in the fossil record. Their bones just fall apart.”
The odds of finding a small, intact fossil with an even smaller intact fossil from its last meal are astronomical, Sullivan said.
“Just think about what has to happen. The carnivore fossil has to be fairly intact—the ribcage, at least, fairly preserved. The fossil has to be of an individual that ate shortly before it died.
“And that food had to have had bones or hard shells because it will keep.”
As it happens, there are a couple of other Zhaoianus fossils from the same fossil bed as this one. Sullivan said that’s likely because they were all found in the bed of what was once an ancient lake, an ideal environment for fossilization.
But those other fossils contained birds, lizards and fish. This is the first mammal found in the belly of a Zhaoianus.
The foot on its belly doesn’t look like it came from a climber, so perhaps the raptor fell from the sky on its hunt. Or maybe the dinosaur was simply gorging on carrion it didn’t have to kill at all.
The find shows that Zhaoianus was opportunistic and ate as much as it could, not unlike the crow it superficially resembles.
“Microraptor was running or possibly gliding, feeding on many different types of vertebrates,” Sullivan said. “It wasn’t specialized and that’s interesting.”
It may suggest the same was true of other microraptors, he said.
But aside from its scientific value, Sullivan finds the fossil compelling because it captures a moment millions of years old, a tiny pixel in a bigger picture of a lost world.
“That makes it neat,” he said.
“A lot of the specimens I work with are skeletons or parts of skeletons that don’t contain behavioral signals. When you see a specimen like this, this individual microraptor ate this individual mammal. We have an interaction between two vertebrates. And that’s rare “.
This report by The Canadian Press was first published on December 21, 2022.
— Follow Bob Weber on Twitter at @row1960
TO SHARE:
JOIN THE CONVERSATION
Anyone can read Conversations, but you must be a registered Torstar owner to contribute. If you don’t have a Torstar account yet, you can create one now (it’s free)
Sign in
Sign up
Conversations are the opinions of our readers and are subject to the Code of Conduct. The Star does not endorse these views.