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Re: Ankle Articulation in Pterosaurs



On Sun, 19 Jan 1997, Amado Narvaez wrote:

> In Wellnhofer's _Illustrated Encyclopedia of Pterosaurs_, however, there
> is a paragraph about ankle/foot articulation with the statement "...the
> ankle could allow right-angled articulation of the foot with the tibia.
> This is an indication of a plantigrade position of the foot (i.e., with
> the sole on the ground) when walking. Thus pterosaurs were not digitigrade
> like birds--walking on the toes--but plantigrade--walking on the soles of
> the feet--like man." (Wellnhofer, p. 57)
> 
> Would this "digitigrade position of the foot" be a dinosaur/bird trait
> that would be useful in explaining to laypeople (myself included) why
> pterosaurs cannot be included among the dinosaurs? (I don't want to use
> the "dinosaurs lived only on the land and could not fly" rationale because
> I want to leave open the option of including birds among the dinosaurs.)

        Except I think it's secondary. There was a poster at SVP I REALLY
should have paid better attention to. It showed what were supposed to be
rhamphorhynch tracks with only the toes touching, and that little backward
toe touching too (put your fingers on the floor, bend the thumb around
backwards so you've got the top of your thumb on the floor, keep the palm
clear- that's what it was like). I got the impression although I didn't
read all that carefully that this is the predicted- and confirmed- track
structure of rhamphorhynchs.
        Now, Pteraichnus- a pterodactyloid- is a completely different
story. The feet were plantigrade, and semi-sprawling, with the manus
prints behind and slightly to the outside of them! Wellnhofer thought the
manus prints should be out farther to the sides, but here's what they did-
if you take the pterosaur and put it in a semi-upright "missing link"
position and bring the wings in to act like crutches, you can get these
prints from a pterodactyloid. So pterodactyloids were not birdlike
runners. This is probably why there have never been any flightless
pterosaurs (well, perhaps on islands). 
        Partial credit will be awarded for the answer "Tyrannosaurus".