Sorry, I pulled the wrong Gatesy citation. The one I listed was the
abstract and not the full paper. The full paper is:

Bipedalism, flight, and the evolution of theropod locomotor diversity
Gatesy-SM; Middleton-KM
The evolution of theropod flight has been characterized as a shift from one
to three locomotor modules. Basal theropods, which were terrestrial bipeds,
had a single locomotor module composed of the hind limb and tail. In birds,
aerial locomotion was acquired with the origination of the wing module and
a decoupling of the hind limb and tail into separate pelvic and caudal
modules. This increase in modularity is thought to have granted birds more
locomotor ''options'' than non-avian theropods. More specifically, an
aerial locomotor system could have eased constraints on the hind limb and
allowed specialization for habitats and lifestyles unavailable to
non-birds. If so, bird hind limbs should be more disparate than those of
non-avian theropods. We addressed this hypothesis by visualizing one aspect
of limb design, the proportions of the three main segments, using ternary
diagrams. Our results show that avian hind limb proportions are much more
disparate than those of non-avian theropods. This broad range of limb
design correlates with a radiation in locomotor diversity founded on three
locomotor modules. We propose that birds have reached regions of proportion
morphospace that are off limits to bipeds with only one locomotor module.
In comparison, the limbs of non-avian theropods are conservatively
proportioned. Despite great variation in body size, theropods other than
birds do not exhibit specializations for locomotion other than terrestrial
bipedalism. Although ether aspects of size and shape need to be analyzed,
the relationship between modular flexibility and morphological disparity
appears to play an important role in theropod locomotor evolution.

It is definitely worth a read if you are interested in the topic of leg
morphology and evolution.


Dan Ferris, Ph.D.
Department of Electrical Engineering
University of Washington
Box 352500
Seattle, WA 98195-2500

Fax: (206) 543-3842
Phone: (206) 616-4936
Alt. Phone: (206) 277-6358

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