Re: AAT Questions...

pete (VINCENT@REG.TRIUMF.CA)
20 Jul 1995 03:00:03 GMT

Ralph L Holloway (rlh2@columbia.edu) sez:
`Alex Duncan's request is a serious one. Please, AAH'ers, please predict
`what the postcranial morphology of the newer Ethiopian fossils (A.
`ramidus) will be like, on the basis of their retention of aquatic
`adaptations. This is a very important question and challenge. R. Holloway.

One doesn't have to be a supporter of AAH to consider what traces
it might present. What can we say about the creatures from the
period in question? For non-aquatic evolution, the original
ancestor has a stronger need to be a gibbon-like brachiator
in order to be prone to bipedalism when it migrates to the
ground. If an aquatic phase is used as a mechanism for
generating bipedalism, the ancestor need not be so erect,
and could have a crouch posture. However that does not
preclude a brachiator for the aquatic ancestor, and at any
rate this characterizes the creature at the beginning of
the phase, not the end.

An aquatic creature would need strong, straight legs for
locomotion, so these would presumably appear early in the
aquatic phase. The need for long brachiator arms would be
gone, so these also should shorten eary.

How would that be different from a post-arboreal ape?
If it was still somewhat arboreal, it would want to
keep its long arms. What about feet? the brachiator
would have had grasping feet, and their loss will
be very dependent on how long the descendant animal
had been on the ground. We presumably have ~4My to
play with. Towards the end of that time, the aquatic
ape would be fully transformed, as in order to be in and
out of the water it would have had to be out of the trees
right at the beginning of that period. The post-arboreal
candidate, however, doesn't have any intermediate destination
to achieve, so it has more time to drift slowly through
its transformation, or it could delay its transition to
near the end of the period, thus it may, though not
necessarily, display more extreme evidence of retained
arboreal traits, such as grasping feet, shorter, bowed
legs, etc.

Thus, my conclusion is, the more modern the structure
of the Ramidus skeleton, the less the aquatic hypothesis
is discounted.

Special disclaimer: I adhere to neither side in the AA
debate, and I have no credentials in physical anthropology
nor anatomy. 

--

==========================================================================

    vincent@triumf.ca   <== faster       %    Pete Vincent

    vincent@freenet.vancouver.bc.ca      % Disclaimer: all I know I

                                         % learned from reading Usenet.