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Re: Phytodinosauria status
David Marjanovic wrote (in response to George):
> The basalmost dinosaur could well have
> been an obligate semisprawling quadruped (and arboreal into the
> as I think, the forelimb evolved gradually into a functioning wing
> (progressively losing its outermost digits in the process) in a lineage
> arboreal dinosaurs,
Here you IMHO run into the same problems as Feduccia -- why should the
forelimbs (and only they) evolve into wings in a quadruped, and why should
they lose digits in an arboreal animal???
IMHO too. Modern gliders are arboreal and quadrupedal, and all are likely
to have evolved from arboreal and quadrupedal ancestors: "flying" frogs,
"flying" squirrels, "flying" possums, "flying" lemur (colugo)...
Most gliding mammals have the gliding membrane (patagium) strung between the
forelimbs and hindlimbs. This gives the largest possible extent for the
gliding surface. This is important for generating lift.
Among gliding mammals, the only exception are "flying" primates, such as
sifakas. Primates are primitively quadrupedal, and most primates move
around on the ground using all four limbs. However, they progress from tree
to tree by bipedal leaps -
most lemurs (and relatives) are "vertical clingers and leapers". The
purpose of the sifaka's gliding surface (small "armpit" patagium and
brachial "mat" of hair) is as much maneverability as lift.
There is no evidence that the ancestors of birds were anything other than
bipedal - unless George is advocating a "Tetrapteryx"-like stage in the
evolution of birds.
Timothy J. Williams
Iowa State University
Ames IA 50014
Phone: 515 294 9233
Fax: 515 294 3163
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