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 remains a mystery. Now, researchers reporting April 21 in Current Biology 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," says first author Derek Larson, a paleontologist at the Philip J. Currie Dinosaur Museum in Alberta and PhD candidate at the University of Toronto. "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. The question is, why did that difference occur when these groups were so similar?"
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.