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Re: Dilophosaurus Forelimb Bone Maladies

The non-reduction of theropod forelimbs [including claws] may have had 
something to do with grooming
and/ or transportation of young from one nest site to another. The only extant 
vertebrates that I can think 
of off hand that transport their young in their forelimbs are primates and 
birds. Both facultative and obligate
From: owner-DINOSAUR@usc.edu <owner-DINOSAUR@usc.edu> on behalf of Tim Williams 
Sent: March 1, 2016 12:05 AM
To: dinosaur
Subject: Re: Dilophosaurus Forelimb Bone Maladies

Mike Habib <biologyinmotion@gmail.com> wrote:

> Good observations - to me, the simply explanation is that it didn't dispatch 
> sizable prey. Most living predators eat things that are effectively bit sized 
> (maybe
>  a couple of bites). That goes for everything from canids to varanids. Yes, a 
> few clades have their one or two big game specialists, but those are rare. 
> Only
> cats really have a bunch of big game hunters, but big felids are just weird.

Yes, among theropods big game hunters were likely the exception, not
the rule.  Tyrannosaurines and velociraptorines come to mind as
exceptions, since there is evidence that they targeted large prey
(i.e. larger or of comparable size to themselves).  But
_Dilophosaurus_ likely preferred small prey.  And because the
forelimbs couldn't reach the mouth, and the forelimbs couldn't readily
contact the ground (not without adopting some yoga-like pose), they
were of little use for prey capture or prey manipulation.

To be honest, I'm surprised that many theropods had forelimbs at all.
In some theropods they were so downsized that they must have been next
to useless (such as _Limusaurus_).  Carnotaurines went the whole hog
and effectively dispensed with forelimbs altogether (though, oddly,
the coracoid was not reduced).  Why wasn't this more widespread?

Then again, I can't readily explain why most non-avian theropods
retained a hallux (first toe) - it was too short and too high to be of
much use.  Some lineages got rid of it (like ornithomimosaurs).  But
most theropods did retain the hallux, and it took on crucial functions
in some lineages (therizinosaurs, deinonychosaurs, birds - weight
support, predation, perching, respectively).  Similarly, the forelimb
took on an extremely useful function in birds.