Re: Re(2): Skin

[ornstn@hookup.net (Ronald Orenstein)]

>Hey, didn't the Russians find a small pterosaur with hair a couple
>of years ago and christened it Sordus pilosus, i.e. Hairy devil?
>If I remember this right, maybe the sentence should read "one
>of the distinctions of being a mammal or a pterosaur..." which is
>of course less impressive-sounding and more fuzzy and conditional
>(just like real-life biology).
>
>Lars Bergquist
>lars_bergquist@public.se

First, there is, I believe, some question as to whether the hairlike
markings on the Sordes fossil are actually hair or something like it, or
just some sort of artifact of fossilization.  Secondly, even if pterosaurs
did have hair this does not mean that pterosaur and mammalian hairs are
homologous structures (the two groups are only distantly related), and for
that matter hair or something like it can be found on bumblebees and even
plants.  Perhaps the statement should read "one of the distinctions of being
a mamma is having MAMMALIAN hair...

But even this won't do at the level of fossils, of course, because (a) hair
generally does not fossilize so we have no idea if all fossil mammals had
it, and (b) we have no idea when hair of the mammalian type arose, though I
would suspect it was before the evolution of the defining mammalian fossil
characteristic (which it in itself pretty arbitrary), the presence of a
single jaw articulation, between the dentary and squamosal, with the loss of
the quadrate-articular articulation (actually retained in the ear ossicles).
I believe that some mammal-like reptiles like Thrinaxodon had pits in the
skull suggesting the presence of vibrissae (which are, of course, hairs,
thoough their function is sensory, not insulating).
--
Ronald I. Orenstein                           Phone: (905) 820-7886 (home)
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