Birds evolved from a group of meat-eating dinosaurs called theropods. That’s the same group that Tyrannosaurus rex belonged to, although birds evolved from small theropods, not huge ones like T. rex.
The oldest bird fossils are about 150 million years old. These ancient birds looked quite a lot like small, feathered dinosaurs and they had much in common. Their mouths still contained sharp teeth. But over time, birds lost their teeth and evolved beaks.
“Birds are living dinosaurs, just as we are mammals,” said Julia Clarke, a paleontologist studying the evolution of flight and a professor with the Department of Geological Sciences at the University of Texas at Austin.
In spite of the physical differences that distinguish all mammals from other species, every animal in that group — living and extinct — can trace certain anatomical characteristics to a common ancestor. And the same is true for birds, Clarke told Live Science.
“They’re firmly nested in that one part of the dinosaur tree,” she said. “All of the species of birds we have today are descendants of one lineage of dinosaur: the theropod dinosaurs.”
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