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On Thu, 15 Sep 2005 11:46:16 -0700 (PDT) Ian Paulsen
> How would this hypothetical first bird be DIFFERENT from
I think it is impossible to predict what the differences would be. The
"first true bird taxon" would have to share, by definition, all the
"birdy" characteristics with Archaeopteryx, so the two birds will be
quite similar in the "important" skeletal features.
The less important diagnostic characters (those that are *not* avian
apomorphies) would be the ones to examine, and those possibilities are
numerous. Maybe a mixture of Velociraptorine and Archie features? Maybe
a mix of troodontid and Archie features?
Depending on whether you are a ground-up believer or a tree-down
believer, the creature would have been either a good runner
(cursorial-style legs) or a good climber (well-developed manus claws and
Other possibilities are:
Longer, heavier tail
Less pneumaticization in the skull and in other bones
Problem is, we won't know for sure until we see a real fossil!
Oh yeah...size/mass. The critter could have been relatively heavy (raven
to turkey size) or small and light (chickadee to robin size). A good
guess would be a creature of roughly the size/weight of Archie, maybe a
wee bit smaller.
Size/mass also enters into the ground-up vs trees-down debate. Modern
tree dwellers/climbers tend to be comparatively lower mass than their
ground dwelling relatives.
At any rate, this taxon probably lived sometime in the late Triassic or
earliest Jurassic. If the genus had a long geologic history, then it
could have coexisted with its descendant genera! Which would make
identifying the real "first" bird taxon a bit difficult, particularly if
the plesiomorphies between the taxa haven't yet been lost.