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



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.