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Re: [dinosaur] Dinosauria reclassification joins Ornithischia and Theropoda in Ornithoscelida



> On Mar 22, 2017, at 11:40 PM, Tim Williams <tijawi@gmail.com> wrote:
> 
> Baron et al.'s phylogeny implies that a supinated, grasping hand is
> primitive for dinosaurs, and they further suggest that "the ability to
> grasp with the manus played an important role in early dinosaur
> evolution".  It's an entirely reasonable hypothesis; but I'm
> skeptical.  I lean toward the view that theropod forelimbs weren't
> really all that useful for grasping (especially prey capture).  Like
> Persons & Currie (2017; dx.doi.org/10.1016/j.jtbi.2017.02.032), I
> suspect that the tendency to ascribe great adaptive significance to
> the freed hands of dinosaurs at least partly reflects our own human
> bias.  Most Triassic theropods and herrerasaurids had short forelimbs;
> as Persons & Currie (2017) put it, it's "difficult to envision them
> grappling with any prey that could not have already been seized by the
> jaws".  So I doubt the 'grasping' manus conferred on early dinosaurs
> some evolutionary edge over other archosaurs (including other bipeds).

I have exactly the same doubts. One of my favorite bits of the Persons and 
Currie (2017) paper is that they take on the prey capture hypothesis directly. 
Since they have set up a solid hypothesis for why bipedalism might be so 
prevalent in lineages with a caudofemoralis muscle (and therefore, by 
extension, why forelimbs get reduced multiple times), it may be worth 
considering if the supinated forelimb anatomy in dinosaurs was mostly a side 
effect of the specific pathway they took for forelimb reduction.

Cheers,

—Mike


Michael Habib, MS, PhD
Assistant Professor, Integrative Anatomical Sciences
Keck School of Medicine of USC
University of Southern California
Bishop Research Building; Room 403
1333 San Pablo Street, Los Angeles 90089-9112

Research Associate, Dinosaur Institute
Natural History Museum of Los Angeles County
900 Exposition Blvd, Los Angeles, CA 90007

biologyinmotion@gmail.com
(443) 280-0181