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>The cursorial (ground-up) model for the origin of avain flight does have
Furthermore, *all* of the close ancestors of Avialae - the group including
Archaeopteryx and later birds - are arguably terrestrial. A great many of
the "bird" characters we see in Archaeopteryx - the wishbone, details of
the wrist, the birdfoot, hollow bones, even the beginnings of a
back-rotated pubis - are found in Theropoda or subgroups thereof. Agreed,
the hollow bones and kinetic skulls of theropods ensure a lousy fossil
record, and I can see how numerous arboreal transitional forms could be
missing. Nonetheless, the evolutionary history painted so far
unambiguously indicates a terrestrial origin for Avialae.
With regard to arboreal adaptation - Alan Feduccia recently published a
study of the claws of Archaeopteryx and birds, and suggested that
Archaeopteryx's claws were more similar to those of arboreal birds than to
cursorial birds, but there are problems with his analysis. First, he was
using the hand claws of Archaeopteryx - something no living adult bird has.
Second, he didn't include any nonavian dinosaurs in his analysis. Thomas
Holtz presented a paper at the recent SVP meeting and showed that the claws
of Archaeopteryx are very similar to those of nonavian theropods.
Christopher A. Brochu
Department of Geological Sciences
University of Texas at Austin
Austin, TX 78712
WORLD CLADISM NOW!