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Re: Metatarsal fusion/nonfusion: birds/theropods



Darren Tanke wrote:

<snip> 

>  Why is it then that birds have fused tarsometatarsals and theropod
> dinosaurs largely don't? Given the great skeletal similarities between both
> groups this morphological difference is quite striking. Bird and theropod
> feet appear so similar at first and yet not when the fusion/nonfusion
> aspects are taken into consideration. Birds large and small have fused
> tarsometatarsi yet theropods large and small don't (elmisaurids excepted).

To your list of questions (which I couldn't answer if my life depended
on it), I'd like to add one more if I may.  I recall reading somewhere
that all known birds except Archaeopteryx also have a fused wrist,
called a carpo-metacarpus.  Is it possible that metacarpal and
metatarsal fusions are controlled by the same gene or gene complex, and
birds had to make do with fused metatarsals because they needed fused
metacarpals?  And if so, why might they have needed fused metacarpals? 
Extra support or rigidity in the wing?  The largest primary flight
feathers are out near the wrist and hand region of the wing, and it
seems reasonable that that's where some of the heaviest stress will be
during flight.  

-- JSW