For years, paleontologists have disagreed over whether birds from the Cretaceous period went out with a whimper — dying out gradually over the course of millions of years — or with a bang — getting wiped out by the same mass extinction event that is believed to have killed off Earth's most recent (and final) wave of dinosaurs.
Now, by conducting an extensive analysis of bird fossils collected from museums all around the world, a team of researchers has provided members of the "bang" camp with what scientists are calling definitive proof that most archaic birds perished in the same mass extinction event as the dinosaurs.
About 65 million years ago, a major ecological shift led to the end of the Cretaceous period, all but obliterating the last living dinosaurs on Earth. What caused the ecological collapse and widespread extinction is often debated, though large-scale catastrophic events like meteorite impact (depicted as comically large in the top image, the meteorite responsible for the mass extinction is estimated to have been close to be upwards of 6 miles in diameter) and volcanic activity are believed to have been the most likely causes.
For as rare as dinosaur fossils are, the discovery of the light and fragile bones of prehistoric birds is even rarer. According to Yale paleontologist Nicholas Longrich, debates over the effects of the mass extinction on avian populations persist due in no small part to the poor fossil record of Late Cretaceous birds.
So what do you do when you've only got a handful of bones to work with? Simple: study everything you've got. To do so, Longrich put together a team of paleontologists and gathered together fossil specimens representing a total of 17 evolutionarily diverse avian species. While all of the specimens were originally discovered in North America, time had seen the samples distributed to museums at every corner of the globe — a fact that had long made their study incredibly difficult.
"The birds that had been discovered hadn't really been studied in a rigorous way," Longrich said. "We took a much more detailed look at the relationships between these bones and these birds than anyone had done before."
The researchers' findings, which are published in this week's Proceedings of the National Academy of Sciences, reveal that all of the specimens examined lived to within 300,000 years of the mass extinction event 65 million years ago. In other words, all of these birds (and presumably many others) had persisted throughout the Cretaceous period — evolving, adapting, and thriving — right up until the mass extinction event.
"This proves that these species went extinct very abruptly, in terms of geological time scales," said Longrich. The research team also notes that not one bird in the wide range of archaic specimens they examined is known to have survived into the Paleogene, the geologic period immediately following the mass extinction event of 65mya.
"There's been growing evidence that these birds were wiped out at the same time as the dinosaurs," Longrich said. "But this new evidence effectively closes the book on the debate."