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Re: Kickboxing Cassowary



Augusto Haro wrote:

Eagles do not wrestle with prey larger than themselves, except for
trained eagles that can grasp wolves. However, I doubt this being
natural behavior. And theropod limb bones, while not pneumatic
according to Britt (1991), have thin walls according to Sereno (1999).

Actually, wild eagles do kill prey much larger than themselves. I have several references regarding the capture of pronghorns by eagles. One study actually weighed the juvie pronghorns, and the average mass was 15 kg. An average golden eagle is about 4.5 to 5 kg. Additionally, we can look at the loads sustained by other pneumatic taxa, such as peregrine falcons, which sustain massive decelerations pulling out of hunting stoops.


In any case, the thin-walled bones of eagles do not make them weak. Pneumatic bones are only weaker than thick-walled bones if the diameter is equal - but bird bones have expanded external dimensions. Avian long bones are actually *stronger* in bending and torsion than their mammalian counterparts. The internal bracing reduces the risk of failure by local buckling, which becomes more probable in thin-walled bones. Failure by buckling is an important factor for a predator struggling with prey, and this appears to be why birds of prey have slightly thickened cortical bone relative to other terrestrial birds (I have a paper in the pipeline on this, actually - here's hoping the reviewers like it). However, it only takes a rather small increase in cortical breadth to vastly decrease the local buckling (again, as in modern raptors and owls). The walls of dromeosaurid long bones were not especially thin compared to many terrestrial birds, even though they might have been thin compared to those of mammals. There isn't any evidence to suggest that they were especially fragile, in any case.

Cheers,

--Mike


Michael Habib, M.S. PhD. Candidate Center for Functional Anatomy and Evolution Johns Hopkins School of Medicine 1830 E. Monument Street Baltimore, MD 21205 (443) 280 0181 habib@jhmi.edu