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Re: Pterosaur morphological evolution



Mark Witton <Mark.Witton@port.ac.uk> wrote:

> Briefly: Buffetaut et al. (2002) rejected the idea that Hatz. was
> flightless because the structure of its humerus, not the limb
> proportions. Indeed, we don't have a single complete bone for Hatz. The
> expanded humeral diaphysis and millimetre-thick bone walls are
> consistent with being a flier, as is the oversize deltopectoral crest.
> For what it's worth, I figure that the massive DPC would be one of the
> first things to go if pterosaurs abandoned flight: the energy and
> material put into developing and sustaining  their flight musculature
> would be totally wasted in a grounded form, so I imagine all
> osteological correlates of it would disappear quite readily.


Thanks Mark.  Like I said, I hadn't read the original _Hatezgopteryx_
description - I was relying on secondary sources re limb elements.  I
agree that osteological correlates of flight would be lost in a
flightless azhdarchid - except for those musculoskeletal traits
(especially of the pectoral girdle and forelimb) that were retained
for quadrupedal locomotion.  As for the deltopectoral crest, the size
and shape (or its very existence) would probably depend on what role
it kept in terrestrial locomotion.


My original point was that a flightless terrestrial pterosaur - unlike
a flightless terrestrial bird - might be expected to retain long
forelimbs, for use in terrestrial locomotion.  But the thin bone walls
and super-long flight finger would have to go.


Jorge Câmara <jorgefdcamara@gmail.com> wrote:

> If Azhdarchids were flightless, how did they defend themselves from
> the big predators? E.g. Tyrannosaurids. Their running abilities would
> need to be at least on pair with giraffes as in the analogy, but they
> look quite clumsy (well, their long limbs look less clumsy than most
> pterosaurs) with their folded wings and membranes? (Or did they lost
> the membranes?) Even with that, were they fast enough to avoid the
> theropods? Is there any study on their "running" capacities?
> If they faced a tyrannosaurid I think their lightness due to their
> ancestor flight path would be a disavantage, against a several tonnes
> Tyrannosaurid. The bill could be of some use, but how powerful was it
> after being also very light?


In the case of  _Hatzegopteryx_, this was found in the Hateg basin,
and there is good evidence that this was an island in the Late
Cretaceous.  If  _Hatzegopteryx_ was a flightless pterosaur (and I'm
not saying it was - I'm simply talking hypothetically), it may not
have encountered any big predators in its Hateg habitat.  At least,
none larger than the velociraptorine _Balaur_ (~2m?).  _Hatezopteryx_
would have been no less vulnerable than a 6m-long sauropod like
_Magyarosaurus_.





Cheers

Tim