[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: book reviews, parsimony and some loose ends

From: Dinogeorge@aol.com

 >... I maintain that bipedality in dinosaurs is an >abnormal
 > vertebrate stance< necessitated by the evolution of the forelimbs
 > into wings, during which the forelimbs lost their portal locomotor
 > function. BADD theory simply says that bipedality happens from time
 > to time, that it happened to dinosaurs, and that this allowed(?)
 > their forelimbs to become wings (why wings?). ...

Actually, I partly agree.

Bipedality may need special preadaptations to evolve.

One point/possibility I came up with while recuperating from surgery is
that there are essentially *two* types of extant arboreal animals (other
than flyers and gliders).

One type is the typical arboreal quadruped, exemplified by squirrels,
lorises, and even most monkeys.

The second type is the long-armed brachiator/leaper. This type has
evolved at least three times that I know of (all in primates, to be
sure): apes (especially gibbons), spider monkeys (new world), and
the indri of Madasgascar.

Now it is interesting that these long armed arboreal forms tend to
use a bipedal walking stance when on the ground (invariably so
for gibbons).

Now the significnce of this to me is how this might relate to the
origin of flight.  A patagium in an arboreal quadruped would tend
to involve all four limbs, resulting in the flying squirrel type
of glider.

However, in a brachiator any airfoil would tend to be concentrated on
the forelimbs, which will also already be strongly muscled and mobile.
Is it possible that this might overcome the difficulty in transitioning
from gliding to powered flight?

Certainly many of the known basal coelurosaurs and maniraptors had
quite long, grasping arms, which might be related to such a brachiating
style ancestry. (After all, that is where *our* long, grasping arms
came from!!!)

swf@elsegundoca.ncr.com         sarima@ix.netcom.com

The peace of God be with you.