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

Re: Palms in



-----Original Message-----
From: Scott Hartman <scott_hartman@hotmail.com>
To: larryf@capital.net <larryf@capital.net>; scott_hartman@hotmail.com
<scott_hartman@hotmail.com>; mbonnan@hotmail.com <mbonnan@hotmail.com>;
dinosaur@usc.edu <dinosaur@usc.edu>
Date: Sunday, July 09, 2000 3:36 PM
Subject: Re: Palms in

>
>But basal tetanurans don't have well developed semilunates.  And more basal
>theropods probably could pronate their limbs.  Are you suggesting that
birds
>evolved after "ceratosaurs" but prior to tetanurans,  or are you suggesting
>that birds evolved flight without a well developed semilunate, and then
they
>and tetanurans evolved them in parallel?
>


I believe that birds got their start in the Triassic. Unfortunately, their
light skeletons are difficult to preserve, (or we would find more of them),
so it is not possible to show a comparative sequence of the evolving
theropod wrist as it may have evolved in fully flighted forms since the
Triassic. However, If you accept Protoavis as a possible avian candidate ,
some conclusions may be drawn.Interestingly, Chatterjee describes Protoavis
as having a semilunate carpal element, but not as advanced as in modern
birds (not as advanced as Archaeopteryx??). He describes the elbow and wrist
joints as being "coupled" automatically, without much muscular effort, and
their motion restricted to a single plane as in modern birds. He states that
Protoavis, however, did not achieve the strength, rigidity, and
reinforcement required to withstand the strain of sustained flight. He
refers to the wrist bones as showing  "primitive morphology" which may
provide clues to early evolution of flapping flight. He mentions the study
by Vasquez that shows the ulnare in modern birds to be large and
interlocking with the ulna and metacarpal III, preventing the manus from
hyperpronating during the downstroke. In Protoavis, the ulnare is small, and
not interlocking, therefor unable to prevent hyperpronation. Protoavis was
designed for powered flight for short distances at cruising speed.

I obtained the above info from his book "The Rise of Birds" (pg80).
Admittedly, I have not as yet obtained his paper on the subject, (something
I`ll have to remedy).