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Re: Pterosaur morphological evolution

Looks to be a very interesting paper!  Pretty impressive for a Masters Thesis 
project, too.  My only disappointment was the caption of the press release 
labeling Quetzalcoatlus as "probably flightless" - considering that Mark Witton 
and I wrote an entire PLoS ONE manuscript debunking this idea (more or less), 
it was a bit annoying.  But so it goes.

One thing I am not sure I agree with (but I'll wait until I get the full paper 
here shortly to really weigh in) is the "unexpected" nature of separation 
between rhamphorhynchoid morphospace and derived pterosaur morphospace.  The 
abstract specifically says "This separation is unexpected, especially in view 
of common constraints on anatomy caused by the requirements of flight".  I see 
this punt a lot: it's the idea that flight is so "difficult" (whatever that 
means) that flying animals must be hugely constrained.  It's a neat idea, but 
it doesn't play out in practice: there is plenty of morphological variation in 
all of the major groups of flyers, especially insects, and at this point I feel 
that saying "flying animals must be constrained" doesn't mean much more than 
saying "walking animals must be constrained".  I'd be curious to know if other 
DMLers have thoughts on this issue.


--Mike H.

On Jul 6, 2011, at 11:12 AM, bh480@scn.org wrote:

> From: Ben Creisler
> bh480@scn.org
> A new online paper:
> Katherine C. Prentice, Marcello Ruta & Michael J. Benton (2011)
> Evolution of morphological disparity in pterosaurs.
> Journal of Systematic Palaeontology (advance online publication)
> DOI:10.1080/14772019.2011.565081
> http://www.tandfonline.com/doi/abs/10.1080/14772019.2011.565081
> Abstract
> Pterosaurs were important flying vertebrates for most of the Mesozoic, from
> the Late Triassic to the end of the Cretaceous (225--65 Ma). They varied
> enormously through time in overall size (with wing spans from about 250 mm
> to about 12 m), and in features of their cranial and postcranial skeletons.
> Comparisons of disparity based on discrete cladistic characters show that
> the basal paraphyletic rhamphorhynchoids (Triassic–Early Cretaceous)
> occupied a distinct, and relatively small, region of morphospace compared
> to the derived pterodactyloids (Late Jurassic–Late Cretaceous). This
> separation is unexpected, especially in view of common constraints on
> anatomy caused by the requirements of flight. Pterodactyloid disparity
> shifted through time, with different, small portions of morphospace
> occupied in the Late Jurassic and Late Cretaceous, and a much larger
> portion in the Early Cretaceous. This explosion in disparity after 100 Ma
> of evolution is matched by the highest diversity of the clade: evidently,
> pterosaurs express a rather 'top heavy' clade shape, and this is reflected
> in delayed morphological evolution, again an unexpected finding. The
> expansion of disparity among pterodactyloids was comparable across
> subclades: pairwise comparisons among the four pterodactyloid superfamilies
> show that, for the most part, these clades display significant
> morphological separation, except in the case of Dsungaripteroidea and
> Azhdarchoidea. Finally, there is no evidence that rhamphorhynchoids as a
> whole were outcompeted by pterodactyloids, or that pterosaurs were driven
> to extinction by the rise of birds.
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Michael Habib
Assistant Professor of Biology
Chatham University
Woodland Road, Pittsburgh PA  15232
Buhl Hall, Room 226A
(443) 280-0181