Seeds may have saved bird-like dinosaurs from extinction

by Mary Caperton Morton
Wednesday, July 20, 2016

About 66 million years ago, nearly three-quarters of life on Earth, including all species of nonavian dinosaurs, were wiped out. However, a few species survived the mass extinction event, including the Neornithes, the ancestors of modern birds. A new study suggests they may have done so by relying on seeds when other food sources were scarce.

“The small bird-like dinosaurs in the Cretaceous, the maniraptoran dinosaurs, are not a well-understood group,” said lead author Derek Larson, a paleontologist at the University of Toronto in Ontario, Canada, in a statement. The question is, he said, why did some die out and others survive when these groups were so similar?

Larson and colleagues focused on more than 3,000 fossilized teeth from four different maniraptoran families (Troodontidae, Dromaeosauridae, Richardoestesia, and Aves, which includes the Neornithes), categorizing their size and shape over 18 million years of evolution, up until the end of the Cretaceous. They found that diversity in teeth remained high right up until the end-Cretaceous extinction event, indicating that the toothed maniraptorans were thriving in a rich and stable ecosystem before they all abruptly died off.

The fact that even highly diverse toothed maniraptorans died out so quickly, while the Neornithes survived, led Larson and his colleagues to suggest in Current Biology that the Neornithes likely had already evolved to be toothless, like modern birds. “We propose that diet may have been an extinction filter and suggest that granivory associated with a [toothless] beak was a key ecological trait in the survival of some lineages.”

The dust and debris kicked up by the meteor impact may have inhibited photosynthesis for some time, wreaking havoc on species dependent on leaves and fruit and also on predators higher up the food chain. But toothless species that were already specialized to live on seeds may have made it through the darkest days and gone on to repopulate the planet.

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