The world was full of birds 66,000,000 years ago. Some of them would have seemed familiar — Vegavis, related to modern geese and ducks, would have looked something like a goose or a duck. Ichthyornis Dispar, though not an ancestor and only a cousin of modern birds, would probably have looked exactly like a gull or tern, but with teeth.
Others were very different — Enantiornithine birds (or opposite birds) looked like flying velociraptors, with long tails that didn’t fan out and snouts rather than beaks. Then there were the maniraptors — dinosaurs that glided around from tree to tree with four wings.
Many palaeontologists have long believed that dinosaurs went extinct gradually, with the Chixculub impact only finishing off what had already begun. But Derek Larson, a paleontologist at the Philip J. Currie Dinosaur Museum in Alberta, studied maniraptoran (bird like) dinosaurs over their last 18 million years, and saw no loss in diversity in that time.
Then 66 million years ago they completely vanished. These were well adapted bird like creatures — and if birds survived, why not them? Why not the other birds, just as well adapted as the modern forms, and much more numerous?
Larson and team have a theory.
phys.org/...
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. Working backwards, Larson and his colleagues hypothesized 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, the researchers 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.
"There were bird-like dinosaurs with teeth up until the end of the Cretaceous, where they all died off very abruptly," says Larson. "Some groups of beaked birds may have been able to survive the extinction event because they were able to eat seeds.”
Now, a healthy note of skepticism from me. Genetic evidence suggests that many of the derived clads of modern birds had already evolved by the end of the Cretaceous. Vegavis (the duck-like bird I mentioned above) was already on the path to the Anatidae (ducks and geese) and certainly ate no seeds. Charadriiforme birds (gulls, terns, waders, sandpipers), are known from the Cretaceous (PDF), one quite remarkably similar to the modern Stone Curlew. These also definitely did not eat seeds.
That said, seed consumption certainly would have kept land birds going at a time when there was no vegetation — the ancestors of doves/pigeons and perchers might not have had anything else to eat.
In a dead world filled with debris, detritus, and ruin, seeds might have been the closest thing to a living food source around. Mammals and crocodilians could get by on the dead ruins of the Cretaceous, but perhaps birds got by on some of the last seeds of the Cretaceous.