How birds out-survived mass extinction that wiped out dinosaursApr 25(AZINS) When the dinosaurs became extinct, may small bird-like dinosaurs disappeared along with giants like Tyrannosaurus and Triceratops. Why only some of them survived to become modern-day birds remains a mystery.

Researchers suggest that abrupt ecological changes following a meteor impact may have been more detrimental to carnivorous bird-like dinosaurs, and early modern birds with toothless beaks were able to survive on seeds when other food sources declined.

"The small bird-like dinosaurs in the Cretaceous, the maniraptoran dinosaurs, are not a well-understood group," said Derek Larson, a palaeontologist at the Philip J Currie Dinosaur Museum in Canada.

"They're 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 Larson, who is also a PhD candidate at the University of Toronto.

The researchers began by studying whether the extinction at the end of the Cretaceous was an abrupt event or a progressive decline simply capped off by the meteor impact.

The fossil record holds evidence to support both scenarios, depending on which dinosaurs are being examined.

Delving into the bird-like dinosaurs, Larson collected data describing 3,104 fossilised teeth from four different maniraptoran families.

Researchers were looking for patterns of diversity in the teeth, which spanned 18 million years.

The data indicated a rich and stable ecosystem over millions of years and suggested that these bird-like dinosaurs were abruptly killed off by an event at the end of the Cretaceous period.

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.

Researchers hypothesised that the last common ancestor of today's birds was a toothless seed eater with a beak.

Coupled with the tooth data indicating an abrupt Cretaceous extinction, they suggest that a number of the lineages giving rise to today's birds were those able to survive on seeds after the meteor impact.

The strike would have affected sun-dependent leaf and fruit production in plants, but hardy seeds could have been a food source until other options became available again.

The study was published in the journal Current Biology.