A few days ago I found a nice microfossil site, which is a concentration of small bones and teeth, most not bigger than a quarter. These rich concentrations tell us a lot about what animals were living together in a given ancient ecosystem. In this particular microsite, I found a very nice dromaeosaur, or “raptor” dinosaur tooth likely pertaining to Acheroraptor, one of the last of these famous bird-like dinosaurs. I was lucky enough to name Acheroraptor a couple of years back, and we found that it indeed is very closely related to its famous cousin Velocirpator, of Jurassic Park acclaim.
As most of us who are interested in dinosaurs know, these raptor dinosaurs shared many similarities with their living bird cousins, including feathers and wings, a wish bone, enlarged brain, a sophisticated respiratory system, and in many cases small in size. So why did the ancestors of today’s birds survive the asteroid impact that ended the Age of Dinosaurs, while their ecologically similar, small, feathery raptor cousins die out? This has been one of the biggest mysteries surrounding the K/Pg extinction. And as it turns out, those tiny fossil teeth are really important in addressing that question.
In new research from my lab that was released last month, we analyzed over 3000 teeth of raptor dinosaurs and early birds from the last 18 million years of the age of dinosaurs in order to understand how patterns of their ecology, as judged by the shape of their teeth and related diets. We used teeth because the small, delicate, and hollow bones of small feathered dinosaurs and birds are destroyed before they even become fossils. But the enamel-covered teeth are hard and resilient, and fossilize well. They showed us that these dinosaurs were a consistent and stable part of the ecosystem leading up to the end of the Cretaceous and their extinct very sudden in geological terms- at the K/Pg boundary.
So how did birds survive? The preserved bird and bird-like dinosaur teeth belonged to animals that ate a variety of other animals- like insects and small vertebrates. However, modern birds (Neornithes) differ in having a toothless beak-so we hypothesized that diet might have been a key factor in their survival. And if the feathered bird-like dinosaurs that ate animals went extinct, perhaps birds survived because they could eat plants, or more specifically, seeds. In the conditions in the wake of the asteroid impact, global forest fires raged and the sun was blocked out by debris ejected into the atmosphere. Plants would quickly lose foliage, which would decimate animals, like raptors, that were tied to photosynthetic food webs. But seeds would be high-energy packets of food that would persist on the landscape, and any animal that could access them would have an ecological advantage. IF the ancestors of at least some groups of modern birds could access this resource in the critical time period immediately after the impact, that could have been vital to the survival to the ancestors of at least some groups of our feathered friends we see today.
Learn more about Acheroraptor here: http://www.rom.on.ca/en/about-us/newsroom/press-releases/scientists-reveal-new-raptor-dinosaur-from-north-america
Learn more about raptor extinction and bird survival here: https://evanslab.wordpress.com/2016/04/21/teeth-of-small-feathered-dinosaurs-tell-a-story-of-extinction-and-survival/