PATAGIA, DINOS HAVE CLASS...

["D.W.Naish" <dwn194@soton.ac.uk>]

Pterosaurs, I think, evolved from archosaurs with quite erect limbs but
secondarily evolved a semi-sprawling posture for flexibility in flight (don't
bother to read the rest unless you're really interested, or you've got loads of
time). 

Let's not launch into the theories on pterosaur wing membranes (=patagia). 
David Unwin and Bakhurina's recent work show that in AT LEAST some pterosaurs
(they studied Sordes) the membrane reaches the ankles and the hind legs were
quite sprawling. Obviously there have been arguments saying that their Sordes
specimens are just post-mortem distortional, but it now appears that they're
right. But this does not condem pterosaurs to a single model. I am of the
opinion that different pterosaurs had different wing configurations:

Smallish (but bigger than Sordes) pterosaurs - Pterodactylus among them - had
membranes reaching the mid part of the thigh (as proven by the Vienna specimen).
Their legs were thus quite free, but still not completely parasagital like in
dinosaurs. No pterosaur walked like a normal bat, with the belly on the ground.
 
Early pterosaurs, and in particular Dimorphodon and its relatives, had totally
free hind limbs and could run bipedally. Pterosaurs seem to have become
secondarily quadrupedal after this, and I don't think that Pteranodon and other
giants could sprint bipedally (as Kev Padian believes.. ). If later pterosaurs
weren't quadrupeds, why did they retain functional hands?

In Pteranodontids the wing membrane attached to the end of the tail. There were
auxilliary membranes between the ankle and inside of thigh which could have 
been used as landing brakes. These pterosaurs freed up their hind limbs and had
extremely flexible, ball and socket joints at the top of the thigh. 

So we can trace some kind of evolution here; pterosaurs evolved from
ornithosuchid-like ancestors and, like them, began as essentially erect-limbed
and able to run bipedally; as pterosaurs became more marine, hind limbs 
became more useful as part of the wing membrane, thus the animals now had to
support weight on their hands also; in many rhamphorhynchoids and
pterodactyloids the wing membrane extended down the thigh; some small 
pterosaurs evolved extremely specialised, broad membranes that reached the 
lower leg; giant, specialised pterosaurs freed the hind-limbs for flexibility
in flight maneouvres and attached the membrane to the tail. 

I don't think that pterosaurs were as adept as climbing as some believe. I 
don't think they hung upside-down like bats. I think that Quetzelcoaltus ate
fish, frogs and things like that and would have taken off by standing erect and
possibly doing a little 'hop'. Tapejara ate fruit!

Controversial? Pa!

"Hello, what have we here..." - - Calrissian, T.E.S.B.

DARREN NAISH
dwn194@soton.ac.uk