[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: semilunate carpal

Killer raptor wrote:
>the semilunate carpal allowed the hand to swing automatically inward in the same lunging motion that brought the forelimbs forward and downward ("predatory stroke"). So, when the hands contacted the prey they were already in position<
The difficulty I have with the concept of the "predatory stroke" explanation for the evolution of the avian-like wrist (and its semilunate carpal) is that the sideways folding of the wrist most likely made the manus a >weaker< grasping mechanism, not a stronger one. Changing the folding orientation of the wrist from flexion/extension to adduction/extension would create a non-coplanar relationship among the forearm (the origin of the major flexion muscles of the digits), wrist and fingers where a coplanar arrangement existed before. I can't think of any animal that is known to have (or had) a noncoplanar two-joint muscle arrangement, although I would be interested in knowing if others are aware of any.  I suspect that such a musculoskeletal arrangement is inherently weak.

Get your FREE download of MSN Explorer at http://explorer.msn.com/intl.asp