Re: Campbell's even crazier than a MANIAC? (archeopteryx

[dinoboygraphics@aol.com]

> > > Now, with respect to retroversion of digit I, perhaps it has not so 
much to do
with perching as it might have to do with the generalised great angle 
between
all digits. There are fossils where even Archaeopteryx seem to have a
retroverted digit I, even if it cannot perch. Metatarsal I seems to be 
rather
freely attached to the rest, so assessing its position seems difficult 
to
assess.<<<

No, because rotation of MT1 like a hinge on the other metatarsals is 
absolutely not how retroversion is accomplished.  Torsion of MT1 during 
development is how it occurs, and it's probably the only way it works.  
The "retroverted" hallices in Archaeopteryx fossils are all 
disarticulated, likewise, there are Archaeopteryx fossils where other 
toes aside from the first look reversed, but they aren't.  The problem 
is that claws are 3d objects that want to roll over as the fossil is 
compressed.  So for example in the Thermopolis specimen every single 
toe is disarticulated, with the hallux rolling one way (probably due to 
being a few degrees in that direction in life) and the other toes 
rolled the other way.  None of the toes are in articulation, and 
looking at the claw position is completely misleading.

Looking at metatarsal morphology shows that MT1 in the specimen does 
not exhibit any torsion, and the toe could not have been offset by more 
than a few degrees.  Don't let an artifact of taphonomy overule the 
morph.


Scott Hartman
Science Director
Wyoming Dinosaur Center
110 Carter Ranch Rd.
Thermopolis, WY 82443
(800) 455-3466 ext. 230
Cell: (307) 921-8333

www.skeletaldrawing.com


-----Original Message-----
From: Augusto Haro <augustoharo@gmail.com>
To: erikboehm07@yahoo.com
Cc: DML list <DINOSAUR@usc.edu>; habib@jhmi.edu
Sent: Wed, 24 Sep 2008 4:42 pm
Subject: Re: Campbell's even crazier than a MANIAC? (archeopteryx



So, agreeing to the ground-up theory, perhaps the most parsimonious 
thing to
admit is that birds had wings of scarce use for locomotion (using thier 
wings
for brooding or courtship), until they get the muscular mass necessary 
in their
pectorals to perform strong flight, without a gliding phase. If they 
could get
into trees (WAIR mediating) their flights might have been longer, but 
the
non-climbing state in the Paleognathae argues against this.

Indeed, apparently among the most basal Palaeognathae and Neognathae 
alive
(tinamous and galliforms) flight is short, and that might be the 
primitive
condition (but not in the also basal Anseriformes), and takes origin 
from the
soil. Perhaps all the Cretaceous birds were not better flyers than 
tinamous and
chickens??.

After all, it is true that based on the recent evidence, flight is more 
basal
than gliding for birds (e.g., tinamous and galliforms do not glide, but 
fly).

Now, with respect to retroversion of digit I, perhaps it has not so 
much to do
with perching as it might have to do with the generalised great angle 
between
all digits. There are fossils where even Archaeopteryx seem to have a
retroverted digit I, even if it cannot perch. Metatarsal I seems to be 
rather
freely attached to the rest, so assessing its position seems difficult 
to
assess.

It seems we arborealists have to capitulate to parsimony 
reconstruction, and
lack of arboreal adaptations.