Subject: Re: Gliders to Fliers? (Was Re: Ruben Strikes Back)

["Larry Febo" <larryf@capital.net>]

>Date: Sat, 25 Sep 1999 23:35:13 PDT
>From: "Matthew Bonnan" <mbonnan@hotmail.com>
>To: dinosaur@usc.edu
>Subject: Re: Gliders to Fliers? (Was Re: Ruben Strikes Back)
>Message-ID: <19990926063514.95727.qmail@hotmail.com>

>(snip)

>How does a stiff-legged, stiff-armed, restricted-handed animal evolve from
a
>tree-dweller in which one finds very different anatomical characters?
>Again, this has nothing to do with systematics or cladograms of any kind.
I
>can just tell you from articulating the forearms of sauropods and
theropods,
>you ain't getting the motions that would appear to be necessary for a
>climbing animal.  While some theropods could have pronated and supinated
>their hands, the range and degree of this would have been far below that
>seen in climbing mammals, and was, in fact, affected by somewhat different
>articulations.

>Again, this is not to outright strike George's bipedality idea as invalid,
>but I'm genuinely interested in why the anatomical features found in both
>dinos and birds are not the ones found in climbing, arboreal mammals or
even
>reptiles.

>My several dollars and two cents,

>Matt Bonnan


This may not be exactly Dinogeorge`s scenario, but it is how I see it. At
first there were arboreal gliders (most likely prolacertiform derived) which
were essentially saurischian ancestors. They were both gliders and climbers
with skin flaps, much like flying squirrels.  Some became more adept at
climbing and became exclusively vegetarian . Among these were prosauropod
ancestors that descended to the ground. Others that remained in the trees
evolved into the ornithischian group ( here I think the backward facing
pubis was an adaptation for more closely hugging tree branches while
climbing). Another group were more adept at the gliding-flying niche, and
these were to evolve into the pteroaur-bird clan.

So, while some developed a climbing habit, and may have had "freer"
forelimbs (ie. the prosauropods and ornithischians), the theropod group were
derived from a group of strictly gliders and fliers that mainly went tree to
tree using their more specialized flight mechanism, and I don`t think these
species did much trunk climbing at all! Hence the restricted arm  movements
of theropods.


______________________________________________________
Get Your Private, Free Email at http://www.hotmail.com