A uniquely well-preserved dinosaur found in southern Alberta is revealing never-before-seen traits that make the animal live up to its name: Ornithomimus, or “the bird mimic.”
The new specimen is the first of its kind to be found with a complete, feathered tail and clear impressions of the skin around the upper leg and torso.
Together, these new features are providing the fullest depiction yet of the plumage sported by Ornithomimus, said Aaron van der Reest, a paleontology student at the University of Alberta who made the find.
“We now know what the plumage looked like on the tail, and that from the mid-femur [thigh] down, it had bare skin,” said van der Reest, in a press statement.
Small, almost downy feathers appear to run along the chest, back, and top of the tail, but not the tail’s underside, he noted.
Similarly, the plumage is scant along the neck and stops altogether at the middle of the thigh, leaving the dinosaur with mostly bare-skin legs.
This pattern of plumage suggests that Ornithomimus likely bore a striking resemblance to at least one modern flightless bird.
“It would’ve looked a lot like an ostrich,” van der Reest said.
This could have important implications for understanding the physiology of Ornithomimus and other theropods, he added, particularly how they controlled their body heat in the warm climate of the Campanian age.
“Ostriches use bare skin to thermoregulate,” van der Rest said.
“Because the plumage on this specimen is virtually identical to that of an ostrich, we can infer that Ornithomimus was likely doing the same thing, using feathered regions on their body to maintain body temperature.” [See a close relative recently found farther north: “Ostrich-Like Dinosaur Discovered in Alaska“]
Eons of pressure under Alberta’s ancient sediments have left the fuzzy feathers “extremely crushed,” according to the statement, but scanning electron microscopes have revealed the their fossilized protein structures in all three dimensions within the rock.
The specimen also includes a distinct set of ridges in the rock, left by the folds of the dinosaur’s skin where the upper thigh met the abdomen.
It’s the first time that this web of skin has been observed in any dinosaur, the researchers said, and its orientation is similar to that found in modern birds.
The team speculates that the placement of this big skin web may have allowed Ornithomimus to fold its legs underneath it more completely than other theropods could — an ability that may have been useful while resting or brooding on a nest, and yet another trait that it shares with birds.
It’s further evidence of how Ornithomimus makes good on its name, said Dr. Alex Wolfe, an Alberta paleontologist who co-authored the research.
“This specimen … tightens the linkages between dinosaurs and birds, in particular with respect to theropods,” Wolfe said in the statement.
“There are so many components of the morphology of this fossil, as well as the chemistry of the feathers that are essentially indistinguishable from modern birds.”
Van der Reest agreed, adding that the new fossils adds important data about the entire family of dinosaurs to which Ornithomimus belonged.
“We are getting the newest information on what these animals may have looked like, how they maintained body temperatures, and the stages of feather evolution,” he said.
The discovery comes on the heels of a similar find in South Dakota, where a new genus of raptor is shedding light on the anatomy and evolutionary relationships of other feathered theropods. [See the South Dakota find: “Giant Feathered Dinosaur, With ‘Unprecedented’ Features, Discovered in South Dakota“]
For now, one of the key questions that remains is how exactly the Dinosaur Park specimen came to be so well preserved.
Upcoming studies into the dinosaur’s death and deposition may help scientists find more — and more complete — fossils with preserved soft tissues, the researchers said, and aid in the effort to tease apart their complex relationships with living birds. [See a dinosaur recently discovered nearby: “‘Hellboy’ Dinosaur Discovered in Alberta Reveals Evolutionary Surprises“]
“If we can better understand the processes behind the preservation of the feathers in this specimen,” van der Reest said, “we can better predict whether other fossilized animals in the ground will have soft tissues, feathers or skin impressions preserved.”
Van der Reest and his advisors report their findings in the journal Cretaceous Research.
van der Reest, A., Wolfe, A., & Currie, P. (2016). A densely feathered ornithomimid (Dinosauria: Theropoda) from the Upper Cretaceous Dinosaur Park Formation, Alberta, Canada Cretaceous Research, 58, 108-117 DOI: 10.1016/j.cretres.2015.10.004