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Re: Pterosaur morphological evolution

Very impressive indeed for a Masters study.  There is certainly a lot
to chew on.  Intriguingly, the non-pterosaurian taxa (_Scleromochlus_,
_Herrerasaurus_, _Ornithosuchus_) fall within the same tight
morphospace as the rhamphorhynchoids.

One comment within the paper that I would perhaps quibble with relates
to the proposed division of ecospace:

    "We know that the Jehol Group in China, spanning some 11
     ma, has yielded large numbers of birds and pterosaurs that
     presumably occupied different ecological niches, the birds
     flitting amongst the trees and feeding largely on insects and
     fruit (two species fed on fishes), and the pterosaurs swooping
     over the lake and feeding on fishes and aquatic invertebrates
     around the margins (Zhou 2004)."

I don't think the pterosaur/bird division of ecospace was so
clear-cut.  For one, the Jehol anurognathid _Dendrorhynchoides_ has
been interpreted as an arboreal, insect-catching pterosaur.  So has
_Nemicolopterus_, another Jehol Group taxon that has been described as
being the most specialized of all pterosaurs for arboreality (with the
caveat that it may turn out to be a juvenile of the tapejarid
_Sinopterus_).  On the other hand, the arboreal and flight abilities
of certain Jehol birds were also not that impressive, especially the
jeholornithids and confuciusornithids - so it's difficult to envision
these birds flitting amongst the trees.  Although many Jehol birds had
perching adaptations that suggest that they were arboreal, and appear
to have been decent fliers.

Further, many Jehol birds appear to have had lifestyles associated
with water, especially wading (e.g, _Yixianornis_, _Hongshanornis_,
_Longirostravis_, _Archaeorhynchus_) - although the diets of
individual taxa varied (catching fish; probing in the mud; feeding on
water plants).  The "two species" that "fed on fishes" are presumably
_Confuciusornis_ and _Yanornis_, considering we have direct fossil
evidence to support fish-eating habits.

So the ecospace occupied by birds and pterosaurs within the Jehol
biota might have had a substantial overlap where aquatic habits were
concerned - and, to a lesser extent, arboreality and/or aerial



On Thu, Jul 7, 2011 at 1:12 AM, bh480@scn.org <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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