Answering why dinosaurs had feathers is as tricky as answering why birds have feathers, only it’s harder because all the remaining dinosaur feathers have been embedded in rock for the last 65 million years or more.
On top of that, birds are still technically dinosaurs. We’ll get to that, but for now the point is that not all bird feathers are for flight. Take the ostrich as an example; its feathers help it regulate its temperature in warm and arid climates. Yesterday, research published out of the University of Alberta concluded that the feathers of the ornithomimus served a similar purpose in the late Cretaceous climate of Alberta.
The ornithomimus specimen that led to this discovery was first uncovered in 2009 in Dinosaur Provincial Park, encased in a giant slab of rock. Because the fossil was missing it head and forelimbs, it was mostly left alone in lieu of higher-priority fossils. Lead paper author Aaron van der Reest was tasked with opening up and preparing this fossil as an undergraduate project. In the tail area, Reest discovered that, remarkably, the dinosaur’s feathers, in addition to its bones, had become fossilized. This is extremely uncommon because softer tissues rarely withstand the hardships of fossilization and sitting for millions of years.
The preservation of the feathers turned out to be unprecedented among all other specimens found on this continent. Said curator of vertebrate paleontology at the Royal Ontario Museum in Toronto, David Evans, in an interview with The Globe and Mail, “It’s drop-dead gorgeous. It is the most completely feathered dinosaur specimen found in North America to date.” Also present was a patch of the ornithomimus’s leg skin, which, similar to modern birds, didn’t have feathers at all.
The basic structure and bodily attachment of the ornithomimus’s feathers bore a strong resemblance to what’s found in ostriches. This led Reest and his co-authors to conclude that the ornithomimus’s feathers were used for thermal regulation, just as ostriches’s do today.
So what’s an ornithomimus? The name literally means “bird mimic” from the Greek words ornith (bird) and mimos (mimic). Don’t get too attached to this etymology, because in terms of how it relates to birds it just confuses things. Another Greek word “sauros” (meaning “lizard”) makes a regular appearance in naming and categorizing dinosaurs, but don’t get attached to this either because as far as reptiles (or more generally sauropsids, which includes both reptiles and birds) go, lizards are more closely related firstly to snakes and secondly to turtles, than they are to crocodiles and dinosaurs (meaning “terrible lizards”). Confused yet? Scientists were too for a long time, and since then the names have all stuck.
So what does the ornithomimus have in common with today’s birds? They’re both saurischian dinosaurs, meaning “lizard hipped” dinosaurs. Saurischian dinosaurs included sauropods (meaning “lizard footed”) such as the long-necked brontosaurus (yes, it’s real again) and theropods (meaning “beast footed”), such as the T. rex and the velociraptor as well as the ornithomimus and modern birds. As far as we can tell, practically all theropods had feathers.
Ornithomimus and modern birds also belong to a further subgroup called coelurosauria (meaning “hollow tailed lizards”), but here is where they finally split off from each other about 85 million years ago. Modern birds all evolved from a subgroup called the maniraptorans (meaning “hand snatchers”), whereas the ornithomimus belongs to a different subgroup called ornithomimosaurs (meaning “lizards like ornithomimus”).