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Re: Emus a Model for Dinosaurs?



So if the center of locomotion shifts in neornithes forward from acetabulum to the knee, as a compensatory shift in the center of mass / gravity (due primarily to a reduction in the caudal series ), can we assume Caudipteryx grade animals also may have moved via a knee driven mechanism? Is there evidence of a reduced 4th trochanter or other modifications in the morphology of the femora that might support this?

As you point out, although the limb segment length / stride length may vary amongst taxa (both living and extinct), the relative orientation of the pes, when contacting the subtrate should be similar, ratites serving as one of the best living analogs ( and visual models, from the artist's perspective ) around today. Rob Gaston produces a nice cast emu foot, I've used one for reference in the studio for years !

Mike S.

In all fairness, "quite different" is relative. Neornithes limb mechanics are very similar to dinosaurs in their articular contacts (even accounting for fusion of the metapodia and the tibiotarsus). Limb excursion (as Tim and Jim and Jim noted) is generated somewhat differently (shifting from the primitive acetabulum based locomotion to the more derived knee-based limb excursion), but the maximum and minimum ranges of motion are very similar, including off-axis motion (which is important). And the actual plantar surface of the feet (and the internal bones, tendons, and ligaments that create it) of modern cursorial dinosaurs are almost identical in how they function to their Mesozoic brethren. Certainly much better than using most extant placental feet to understand the biomechanics of Mesozoic mammal trackways.

Scott

Scott Hartman
Science Director
Wyoming Dinosaur Center
110 Carter Ranch Rd.
Thermopolis, WY 82443
(800) 455-3466 ext. 230
Cell: (307) 921-8333

www.skeletaldrawing.com

-----Original Message-----
From: jrccea@bellsouth.net
To: andreasj@gmail.com; dinosaur@usc.edu
Sent: Fri, 27 Oct 2006 8:41 AM
Subject: Re: Emus a Model for Dinosaurs?

They are.
JimC

Andreas Johansson wrote:

Aren't neornithine leg mechanics quite different from those of
"classical" theropods?


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