Re: Upright bipedalism in dinos

[ornstn@hookup.net (Ronald Orenstein)]

Skip Dahlgren writes: 

>First, thanks to all who responded to my arachnid question.  The critter was 
>variously identified as an amblypygid, a "wind scorpion," a "sun spider," a 
>"whip scorpion" or "false scorpion," and a solpugid (or solifugid), with this 
>last being the odds-on favorite

As amblypygids and solifugids (really the only two choices; the other names
apply to one or the other) look very different from each other, a quick
check in a picture book on inverts ought to solve your puzzle.


>My question:  are there any known fossil dinos which may have had an erect 
>posture similar to that of the penguins?  The secondary question would be: 
>are there any other birds (ancient or modern, other than those leading to the 
>penguin line) which show similar adaptations (primarily erect posture, but 
>also horizontal/quadrupedal locomotion)?

You must understand that the upright stance of penguins is a consequence of
their hind limbs being reoriented to the posterior end of their bodies as an
adaptation for swimming.  You can see the same sort of thing to a lesser
degree in some other seabirds (notably the extnct Great Auk);  loons have
shifted their feet both backwards and sideways, so that they can barely
progress on land at all (as did the extinct hesperornithids).  I would
therefore not expect to see such an adaptation in a purely terrestrial animal.

Mind you, birds can alter their posture, so that they can at times have
their bodies quite vertically aligned (a robin on your lawn can do this);
and many open-country birds regularly sit quite upright.  A prize case is
the peculiar Plains-Wanderer from Australia, a superficially quail-like
shorebird relative that literally runs around on tiptoe in an extremely
upright posture.  However, these are behavioural posture changes, not the
sort of obligate postural shift you see in a penguin.

I don't think anyone has argued that although (say) Tyrannosaurus may have
normally held its body parallel to the ground, it could not rear upright if
it wanted to.
--
Ronald I. Orenstein                           Phone: (905) 820-7886 (home)
International Wildlife Coalition              Fax/Modem: (905) 569-0116 (home)
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