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



On 03/27/2017 02:17 AM, Tim Williams wrote:
> Ruben Safir <ruben@mrbrklyn.com> wrote:
> 
>> in essence there is a cost to the forelimbs not being modified
> 
> 
> If by "modified" you mean shortened - then it's been argued that there
> is a cost to bipeds (especially cursorial bipeds) in retaining long
> forelimbs (e.g., Carrier et al., 2001; Persons & Currie, 2017).  This
> cost can be mitigated by evolving ways to fold/flex the forelimbs
> close(r) to the body.
> 


After adaptation of bipedal locomotion, you would think that there are a
number of archaic body forms which would have a high cost to maintain.
Not just the length of arms, but also side to side lizard movement would
have a high cost to maintain, having arms sprayed out, the stiffness of
the spinal column, the position of the inner ear, and the connection of
the tail to the pelvis.  You wouldn't want a dragging tail.  In all
these cases, maintaining the inherited form would be a high cost.