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Re: Pterosaurs and ABSRD (sensu Williams)



Dermal structures are varied and can develop in anytweird stuff. Of course hairs
and scales may have similar chemical components and develop in different paths.
But I think that is far from the Longisquama question. The question here was not
that dermal stturctures could turn into hairy integument, but that Longisquama
structures wer homologous to feathers and could be a model for their
development... that was Ruben's and Feduccia assertion.
I'd go with Prum's model of the development of a feather anytime. I visualize
early protodinosaurs as spiny creatures that kept evolving into getting a more
and more sophisticated coat of insulatory quills (may be helping them to jump
from brach to branch like squirrels, if we want to defend the Trees Down Theory)
that finally started to show signs of branching.
The 'velcro' effect of the new dromaeosaur arms integument seems to support
this.

Dinogeorge@aol.com wrote:

> In a message dated 5/20/01 1:01:30 PM EST, luisrey@ndirect.co.uk writes:
>
> << Should be clear by now that this is not any evolutionary step towards a
> true feather. >>
>
> Longisquama "feathers" were probably not on the evolutionary path toward true
> feathers, but they could very well be structures that evolved independently,
> along a different path, from earlier dermal structures that did evolve into
> feathers in theropods.
>
> I suspect some Permian and Triassic prolacertiforms, among which several
> lineages are well known to have been arboreal climbing and gliding reptiles,
> already had such dermal structures. In pterosaurs, these developed into a
> hairy coat; in certain archosaurs, these developed into scutes; in other
> archosaurs, these developed into true feathers. The protein in feathers would
> have had a multitude of uses, just as hair in mammals developed into
> fingernails and claws, glyptodont armor(??), armadillo shells, rhino horns,
> and pangolin scales.

--
Luis Rey

Visit my website on http://www.ndirect.co.uk/~luisrey