After an asteroid impact that killed carnivorous bird-like dinosaurs some 65 million years ago, birds with toothless beaks survived on seeds in the absence of other food sources, say Canadian researchers.
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When the dinosaurs became extinct, plenty of small bird-like dinosaurs disappeared along with giants like Tyrannosaurus and Triceratops.
Why only some of them survived to become modern day birds remained a mystery, researchers noted.
"The small bird-like dinosaurs in the Cretaceous -- the maniraptoran dinosaurs -- are not a well understood group. They are some of the closest relatives to modern birds and at the end of the Cretaceous, many went extinct, including the toothed birds but modern crown-group birds managed to survive the extinction," said first author of the study Derek Larson.
The team of researchers investigated whether the extinction at the end of the Cretaceous was an abrupt event or a progressive decline simply capped by the meteor impact.
Larson and his colleagues looked for patterns of diversity in the teeth, which spanned 18 million years (up until the end of the Cretaceous).
"The maniraptoran dinosaurs maintained a very steady level of variation through the last 18 million years of the Cretaceous. They abruptly became extinct just at the boundary," Larson said in a paper that appeared in the journal Current Biology.
The team suspected that diet might have played a part in the survival of the lineage that produced today's birds and they used dietary information and previously published group relationships from modern day birds to infer what their ancestors might have eaten.
Larson and his colleagues hypothesized that the last common ancestor of today's birds was a toothless seed eater with a beak.
"There were bird-like dinosaurs with teeth up until the end of the Cretaceous, where they all died off very abruptly," said Larson, adding, "Some groups of beaked birds may have been able to survive the extinction event because they were able to eat seeds."