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Re: polarity of bipedality in dinosaurs



In a message dated 96-09-22 15:09:04 EDT, you write:

>     How much Triassic "dino-bird" material is known?  A lack
> transitional fossils for what was probably a pretty small group at
> the time is hardly surprising given the sparsity of remains of even
> the relatively common animals from the Triassic.  This absence of
> material, and even if it does not work against your theory,
> certainly doesn't support it unless you have a great deal more
> material from your hypothetical transitional form.

I'm not looking for support for my theory here; I'm saying that evidence
previously used to support pre-dinosaurian, thecodontian, bipedality doesn't
exist.

Besides, there >are< fossil archosaurs that fit my criteria of what some
dino-birds might have looked like. These include _Longisquama_, various
megalancosaurids (or drepanosaurids), and whatever small, birdlike thing has
gotten mixed into the type specimen of _Protoavis texensis_. If hard evidence
for BCF, in the form of real fossil dino-birds (for example), were abundant,
it would have become the standard theory long ago.

The major point I keep trying to make is that BCF is a single, unified theory
that >explains< the existence in dinosaurs, particularly theropods, of a
number of characteristics that standard BADD (birds are dinosaur descendants)
theory just logs _ad hoc_ without adequate explanation. This makes BCF
>better< than BADD. Among these characteristics are:

Loss of outer digits of the manus in theropods
Bipedality and forelimb reduction in theropods
Large size of theropods versus small size of birds
Hollow-boned and pneumaticized skeletons of theropods and primitive dinosaurs
Stiffened tail in theropods
Oversize manual and pedal unguals in theropods
Maniraptoran forelimbs of certain theropods
Retroverted hallux of most theropods
Keeled sternum in theropods at and above the phyletic level of _Allosaurus_
Presence of a furcula in certain theropods
Scarcity of pre-_Archaeopteryx_ "birds," and existence of all so-called "bird
precursor" dinosaurs in strata >younger< than that of _Archaeopteryx_
Microfossil theropod teeth in Jurassic strata
Presence of feathers in birds versus apparent lack of feathers in most if not
all theropods

BADD and BCF are in substantial agreement that birds and theropods are
intimately related, and agree in most of the major features of dinosaur-bird
phylogeny.