Fossil teeth suggest that seeds saved bird ancestors from extinction
The team of researchers, which also included David Evans of the Royal Ontario Museum and the University of Toronto and Caleb Brown of the Royal Tyrrell Museum of Paleontology, began by investigating 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 fossilized teeth from four different maniraptoran families. Some were already published, but much of the information came from Larson's own work at the microscope, cataloging the shape and size of each tooth.
In the end, the tooth data favored the latter interpretation. "The maniraptoran dinosaurs maintained a very steady level of variation through the last 18 million years of the Cretaceous," says Larson. "They abruptly became extinct just at the boundary."
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."
Source: Cell Press [April 21, 2016]