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Query: Evolution of Pterosaurs



"Pterosaurs -- so close to dinosaurs, yet so far away."

(This following message has nothing to do with dinosaurs, well, almost.  >8:)
 I bet most of you will be happy that I am not writing about dinos again.)

Where exactly did the great pterosaurs originate?  I recall that they came
along a little before the Dinosauria.  Pterosaurs seem to share quite a few
similarities with dinosaurs, their skeletal structure, insulation, birdlike
qualities, warmbloodedness -- but I am aware that most of the pterosaurs'
dinosaurlike qualities evolved separately.  As pterosaurs developed more,
they started looking like furry, giant seabirds with wing membranes instead
of wings -- boy, does Quetzalcoatlus look like a pelican or what? :)  But the
early pterosaurs looked peculiarly like the early dinosaurs (such as Eoraptor
and Herrerasaurus).  
 
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There's a primitive dinosaur if I ever saw one.  ;)

Pterosaurs, as many have suggested, may have risen from the thecodont(s) that
gave rise to the dinosaur empire.  Bakker has suggested that little
squirrel-sized Lagosuchus may have been such a thecodont (it looks close to
both dinosaurs AND pterosaurs).  Bakker, if I remember correctly, envisioned
Lagosuchus as an arboreal, leaping predator, that maybe had descendants with
flight membranes across their arms to make tree life easier.  Then they
figure out, hey, why don't we just go ahead and rule the skies?  So they
modify their fourth finger to support a longer membrane, modify their bodies,
evolve endothermy and insulation -- and become the gulls of the Mesozoic.

Hmm, sounds a little off.  ;)  If this isn't right, what do we do?

Here are a few questions I just have to ask:

1) Why would little thecodonts becomes arboreal in the first place?  To fill
in an unoccupied niche?  Escape from ground-dwelling predators?  

2) Did the skin membrane even evolve as a gliding adaptation?  (Must have...)

3) How did evolution go from thecodonts to actual genuine pterosaurs?  Isn't
there a large gap in the fossil record where the transition took place?

4) If in fact thecodonts evolved skin membranes as gliding adaptions in the
trees, how did they go from membranes to actual wings?  They did achieve
powered flight, correct?  And they must have had a reason for powered flight,
since they sure didn't need it in the trees...

5) The pterosaurs seemed to be fish-eaters from the very beginning.  How did
they go from arboreal thecodonts to sea-going ichthyovores?

6) Suppose pterosaurs and dinosaur DID evolve from the same common ancestor,
a lagosuchid.  It is currently accepted that both pterosaurs and dinosaurs
had endothermic adaptations, or something close to that (a system for keeping
in heat, sometimes gigantothermy as in large sauropods).  Did the two groups
of archosaurs evolve endothermy separately?  Or did they both inherit
endothermy from the common ancestor?

7) Pterosaurs evolved a wide variety of crests, like the lambeosaurine
hadrosaurs.  Was this for counterbalancing the animal in air, or for
sexually-related reasons?

8) Their thecodontian ancestors were quadrupedal/bipedal animals that walked
like any old thecodont.  But as pterosaurs evolved their wings, it has been
suggested that they reverted back to being total awkward quadrupeds when on
land, that folded their wings up against their bodies and balanced on their
arms and sprawled-out hind limbs.   At least that position goes for the
short-tailed pterodactyloid pterosaurs.  But I have often seen
rhamphorynchoids, such as Dimorphodon, in a fully bipedal run.  Why the
difference?

9) Yes, and what did the pterosaurs do when birds came along in the
Cretaceous?

I could go on for a while longer, but once this discussion gets started my
other questions will probably be answered.

Ciao!

Raptor RKC (Rachel Clark)