Emu crouched, one-foot on the ground running clue to dinosaur bipedal running (free pdf)
Ben Creisler
Pasha A. van Bijlert, Anne S. Schulp, and Karl T. Bates (2024)
Muscle-controlled physics simulations of bird locomotion resolve the grounded running paradox
Science Advances 10(39): eado0936
DOI: 10.1126/sciadv.ado0936
https://www.science.org/doi/10.1126/sciadv.ado0936
Humans and birds use very different running styles. Unlike humans, birds adopt “grounded running” at intermediate speeds—a running gait where at least one foot always maintains ground contact. Avian grounded running is a paradox: Animals usually minimize locomotor energy expenditure, but birds prefer grounded running despite incurring higher energy costs. Using predictive gait simulations of the emu (Dromaius novaehollandiae), we resolve this paradox by demonstrating that grounded running represents an optimal gait for birds, from both energetics and muscle excitations perspectives. Our virtual experiments decoupled effects of posture and tendon elasticity, biomechanically relevant anatomical features that cannot be isolated in real birds. The avian body plan prevents (near) vertical leg postures, making the running style used by humans impossible. Under this anatomical constraint, grounded running is optimal if the muscles produce the highest forces in crouched postures, as is true in most birds. Shared anatomical features suggest that, as a behavior, avian grounded running first evolved within non-avian dinosaurs.
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Ben Creisler
New Scientist
3 min.
Adrian Boeye
Reading over this publication is really quite interesting (I strongly suspect I will be rereading this article several times over the next few weeks), and a lot of these findings converge with other work. While I am not sure we can draw direct one to one comparisons from avian dinosaurs to extinct theropod dinosaurs due to some fundamental differences in anatomy (biggest of these being the tail or lack thereof), there is still a lot that is really useful here, and contradictory to my previous point these are due to other similarities in anatomy (particularly the structure of the leg and anterior COM). Given the findings about anatomy and muscle optimums for energy efficiency and performance, the conclusions are pretty easy to follow and concur with the direct observations. The inevitable follow up question for a lot of us, and I suspect people who are interested in the really large theropods, is what does this mean for our models of their running performance, and what is the posture that produces the highest speed? I don’t know and I am curious to see what others have to say or speculate upon, but hopefully we get some more research on this subject over the next few years, it should be quite interesting.
At the very least, I do think there is some interesting speculation that can be done with regards to duty factor, types of locomotion, and how quick an animal can move. Looking back at Sellers et al. 2017, even the fast input they used had a pretty high duty factor, and of course the grounded gait had a duty factor that had no aerial phase. That said, both of these inputs still put out a fairly respectable pace. Although their model of T. rex does not represent a supercharged sprinter, I think there is a fair argument to be made that even with a fairly high duty factor an animal can move at a pretty decent clip while considering the anatomy of an animal and overall muscle performance. Certainly the findings of this new study seem to suggest a fairly dynamic kind of motion that allows for an efficient and reasonably quick gait, even if that style of locomotion seems weird to our eyes.