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dinosaur hip mechanics (was Re: Big Dinosaur Print)



Dan:

The acetabulum (hip socket) of many dinosaurs has a process called the antitrochanter, essentially a bump on the posterior side of the acetabulum. On the posterior (back) aspect of the femur (thigh bone) is a notch or fossa into which the antitrochanter articulates. It is physcially impossible in many dinosaurs (not all, but many) to rotate the femur much past vertical if the body is horizontal. In other words, in a theropod with a horizontal vertebral column, the femur can swing forward in flexion (Nick Hotton III had reported a value of approximately 60 degrees or so in his 1980 paper in the "A Cold Look at the Warm-Blooded Dinosaurs" book) but is physically stopped by the antitrochanter once it passes a vertical orientation -- in other words, like ourselves, many dinosaurs appear to have had limited femoral extension.

Furthermore, as Greg Paul and others have pointed out, rocking the body into a more vertical position would have strained the pelvic musculature, especially the adductor muscles that hold the femora close to the body.

I am not a theropod expert, however, and I'm sure someone else on the list could enlighten us further on the extent of theropod dinosaur leg movements. From what I can tell from my studies of the hip joint and should joint in sauropods, motion was relatively restricted (big surprise!), but many sauropods have a reduced or almost absent antitrochanter. It seems likely that sauropods had a more pendulum-like leg motion than theropods because of this, but wait for the papers -- oh, how much I wish I had this stuff out now! =)

I may as well take this opportunity to announce that I have accepted an assistant professor at Western Illinois University in their biology this fall (as a functional morphologist) and will be defending the dissertation on sauropod locomotion in April. I will fill you all in on my new address when the great move is finished. Anyway, now you all have to bow before my power as a member of the academic community -- just kidding!!!! =) =P

As the geologist Jonathan Cooley once related to me, "In a Ph.D. program you learn more and more about less and less until pretty soon you know everything about nothing." =)

Matt Bonnan
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