It’s not hard to see why paleontologists call ornithomimosaurs the “ostrich mimic” dinosaurs.
The term is a little backwards. If anything, today’s ostriches are mimics of their distant Mesozoic cousins. But, all the same, Struthiomimus and Gallimimus of Jurassic Park fame had the same toothless, long-necked, burly-legged look exhibited by many of today’s flightless birds, albeit with long, three-clawed hands added on. And thanks to a spate of recent discoveries in Canada, we now know that the ornithomimosaurs shared the same plumage pattern as their living relatives, too.
For almost a century artists envisioned dinosaurs like Struthiomimus as shaved, clawed ostriches. And even as evidence mounted that these dinosaurs were fluffy, the fossil feathers themselves remained elusive. Finally, in 2012, paleontologist Darla Zelenitsky and colleagues announced evidence of dinofuzz on three specimens of Ornithomimus from the 75 million year old rock of Canada. While the juveniles seemed to be mostly fuzzy, the arms of one of the adults seemed to show evidence of large, long feathers that would have been superficially similar to those seen on the arms of modern ostriches.
Now Aaron van der Reest, Alexander Wolfe, and Philip Currie have added another fluffy Ornithomimus to the mix, and this one provides a new interpretation of just how feather-covered this dinosaur was.
Discovered in 2009 within Alberta’s Dinosaur Provincial Park, the partial Ornithomimus skeleton preserves soft tissue details never before seen in this species. Simple, wispy feathers run along the neck, chest, back, and tail, and the flexed lower leg is wrapped in fossilized skin.
Ornithomimus wasn’t completely covered with fluff from head to toe, van der Reest and coauthors conclude, but instead had a relatively even covering of simple fuzz over most of the body, with expanded feathers on the arms and naked legs. This distribution of plumage recalls the arrangement on ostriches, emus, and their relatives, the bare-legged look helping the birds dump excess heat to the cooler air. In short, Ornithomimus was an even better ostrich mimic than paleontologists expected.
van der Reest, A., Wolfe, A., Currie, P. 2015. A densely feathered ornithomimid (Dinosauria: Theropoda) from the Upper Cretaceous Dinosaur Park Formation, Alberta, Canada. Cretaceous Research. doi: 10.1016/j.cretres.2015.10.004