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On Fri, 8 Dec 1995, Ronald Orenstein wrote:

> GO writes:
> >It's nice to be corrected in the BCF direction! Reversible ankles, you say?!
> >Love it!
> Reversible ankles are also found in two cats, the Margay and the Clouded
> Leopard.  They permit a quadrupedal animal to descend a tree headfirst or to
> hang from a limb by its hind feet while grasping prey (that's why a Margay
> can come down a tree headfirst and a domestic cat can't).  They might not
> show up in an arboreal theropod - after all many arboreal or partly arboreal
> mammals (like other cats) don't have them, and they possibly would be less
> likely in a biped (which could get down a tree by shinnying tail first or,
> like a tree kangaroo, simply jumping out of it.)  I don't know any bird that
> has such a structure.  However, if any such modification did show up in a
> suitable theropod candidate (allowing for the general differences between
> dino and mammal ankle joints - and them might be somewhere else on the leg
> in a dino) it would be, I think, pretty good evidence of arboreality.

        Bakker thinks that Othnielia and his pet dino Drinker (relatives of 
the hypsilophodonts, 5-6 and 2-4 feet respectively, Late Jurassic of 
Colorado, Wyoming, and Utah/ Wyoming) were 
both arboreal forms. He cites a large, opposable first toe, and noted 
something about the ankles- I think it was that they could rotate. I'm 
guessing that he was speaking about the reversible ankle thing.
       I just checked out the ankles for myself, right out of my window. The 
squirrel's toes end up pointing directly out to the sides. 
        Am I right in remembering that some pterosaurs also have reversible 
        -nick L.