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Re: polarity of bipedality in dinosaurs (real long--TOO long)



For Jonathan Wagner, 96-09-23 14:10:48, a reply.

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))
)) For clarity, I have bracketed my responses to the Wagner posting
)) inside these "semi-boxes" made out of close-parentheses.
))
))                                    --Helpful George
))
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[Note that because of George's helpfulness, the text that's *not* set
 off by anything is *not* original text from this message.  It's
 quoted from Jonathan Wagner.  Your humble moderator.  -- MR ]

At 09:57 AM 9/23/96 -0500, Dinogeorge wrote:
>[Jeff. Martz wrote...]
>>     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.
        That's going a long way.  You may be prepared to simply discard all
of the evidence concerning the proliferation of bipedality amongst
archosaurian taxa, but I would certainly look very skeptically on any theory
which requires such a seemingly casual rejection of so much work.  While it
is true that the fossil record is not complete in this area, a theory which
requires one to ignore a significant body of scholarly work cannot be as
favorable as one which addresses (even in an abbreviated manner) that work.

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))
)) The "rejection" is not casual by any means. I've read practically all the
)) papers that describe bipedal thecodontians (indeed, almost all the papers
)) that describe thecodontians of any kind), and I've found many (though by
)) no means all) are colored by the desire to establish one or another kind
)) of thecodontian as a dinosaur ancestor. When you actually look at the
)) available material, the arguments for any kind of bipedality among
)) thecodontians become pretty slim. Bipedal thecodontian dinosaur ancestors
)) exist mainly in pop-sci dinosaur publications where the science doesn't
)) get quite the scrutiny that it should.
))
)) The challenge I would post here is, simply tell me the names of the
)) thecodontian genera that you think were erect, obligatory or habitual
)) bipeds. Tell me which skeletal characters argue for this mode of
)) locomotion. Tell me why you think these genera were closely related to
)) the dinosaurian clade, and tell me why you think these genera were
)) >not< dino-birds. Then I'll go into my collection of archosaur
)) literature, look up the material available for your genera, and see
)) whether I agree with your assessment. I've already done just this for
)) myself; but perhaps I've missed something somewhere.
))
)) Heck, you're right there at Texas Tech. You can go right to the
)) collections and handle the type material of _Postosuchus_ without even
)) having to drive to a different city!
))
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        Should we take this to mean that you don't believe in bipedal
pterodactyls either?  For certainly they arose from stock closely realted to
the dinosaurs.  Did they develop from quadrapedal animals while "dinobirds"
were going bipedal?  If so, when did they find the time to specialize their
forelimbs?  Funny, they're beginning to sound like "dinobirds".  I suppose
it could happen...

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))
)) Right, I don't think pterosaurs were bipedal--or at least, most of them
)) weren't. Some of the most primitive ones had a large patagial membrane
)) (well preserved, with hair traces of some kind, in _Sordes_) that would
)) have made bipedal walking virtually impossible. The pelvic anatomy of
)) many (though again, not all) pterosaurs also mitigates against bipedal
)) walking. But the main reason they were probably not bipedal is simply
)) that they were not fully erect (boy, would Kevin Padian disagree here).
)) Pterosaurs, however, did indeed arise from "stock closely related to
)) dinosaurs," a different branch of small, arboreal archosaurs similar to
)) the dino-birds from which dinosaurs and birds evolved.
))
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>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),
        If I am correct, these are poorly understood forms.  Except for that
one with the long scales on it's back, which looks about as likely to learn
to fly as a goat.

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))
)) Fly _Longisquama_ did not; but >glide< it probably could. Every paper
)) on this creature suggests that it was a glider of some kind. Contrary
)) to your statement elsewhere in this post, I do not casually or lightly
)) disregard the work of others, but in this instance you seem to have done
)) just that yourself!
))
)) _Megalancosaurus_ is now known from several nearly complete skeletons.
)) It was a highly derived, small ornithodiran archosaur adapted for
)) climbing, with large, strongly curved manual and pedal claws. There is
)) no way it gave rise to any dinosaurs or birds we know of (wrong
)) phalanx counts, for one thing); it was just another example of the
)) highly diverse but almost entirely cryptic (as yet) radiation of
)) arboreal archosaurs. Such forms are "poorly understood" solely in the
)) context of BADD theory. BCF accounts for them fairly well.
)) 
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>and whatever small, birdlike thing has gotten mixed into the type
>specimen of _Protoavis texensis_.
        So certain are you that Protoavis is a chimera?

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))
)) Heh, heh! >You're< the fellow at Texas Tech University where the
)) holotype specimen is located; you tell me! Some pretty big guns
)) have taken some pretty big potshots at _Protoavis_, such as
)) John Ostrom, the Kladist Krew at the American Museum of Natural
)) History, Jacques Gauthier, and others. I got pretty close to
)) examining the material myself in the 1980s when I passed through
)) Lubbock doing some dino-sightseeing (saw _Postosuchus_ then, too). The
)) point here is that I am >not< certain that _Protoavis_ is a chimera, and
)) indeed I would >rather< see it as a protobird or dino-bird. What does seem
)) certain is that there is something birdlike in the holotype, which may or
)) may not have non-avian material in it. The birdlike material (which may be
)) all of the holotype or just a part of it) fits with BCF better than with
)) BADD.
))
)) As I just said, you're there at Texas Tech. Why not drop in on Sankar
)) and ask to see the specimens? Then tell us all what >you< think you've
)) seen.
))
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>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.
        I'm afraid that this doesn't always hold.  There was abundant
evidence, even some papers published, arguing for active dinosaurs, and it
was ignored.  That is beside the point....

>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
       The one thing I have seen consitantly throughout the best, longest
lasting, most robust theories is that they don't explain everything at once.

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)) 
)) And you are incredibly off base here! The best, longest-lasting, most
)) robust theories are PRECISELY those that explain many seemingly
)) disconnected observations within one framework. To name a few:
)) Newtonian mechanics and the Newtonian theory of gravitation, which
)) ascribed one cause to the motions of all massive objects from apples
)) to planets; Darwinian evolution, which ascribed the manifold diversity
)) of life on earth to the single phenomenon of natural selection;
)) Maxwell's equations of electromagnetism, which unified all
)) electrical and magnetic phenomena into a single theory; the atomic
)) theory of matter, which describes the macroscopic properties of matter
)) solely in terms of the interactions among atoms; continental drift,
)) which describes the earth's geology solely in terms of the unifying
)) concept of moving continents; the kinetic theory of gases; Einstein's
)) theory of relativity; quantum theory; the standard model of particle
)) physics; the Big Bang theory of the origin of the universe; Kepler's
)) laws of planetary motion; and so forth. The "theories" that do not
)) withstand the test of time are precisely those that simply patch over
)) difficulties and inconsistencies with mountains of _ad hoc_ "quick
)) fixes," much like BADD dinosaurology.
)) 
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        Your theory requires that a group of animals stay around for around
200my, not changing very mush, spitting out radiation after radiation of
critters.  It is not more parsimonious than assuming that these critters
developed from each other.

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))
)) You've completely misread my theory. Dino-birds most emphatically did
)) >not< "stay around for around 200my, not changing very much..."!! They
)) seem to have been an >extremely< diverse group, within the parameters of
)) being arboreal climbers, gliders, and fliers. They existed for part of
)) the Triassic and most of the Jurassic, by the end of which they had become
)) what everyone presently considers "true" birds. They sired several major
)) theropod radiations, and those were just the large, ground-dwelling forms
)) of the dino-birds. There >must< have been a tremendous amount of evolu-
)) tionary experimentation going on among the dino-birds as they became ever
)) more perfectly adapted to living in trees, gliding, and flying.
))
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>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
        If they were bipedal, why would they need a wide hand?  Two or three
solid meathooks sounds like it would work fine.  Still, interesting question.

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)) 
)) Humans are bipedal, and have a wide hand. We know that dinosaurs
)) started out with five manual digits, because all sauropods and most
)) ornithischians had them. If you believe that dinosaurs shared a common
)) ancestor, then that ancestor had a pentadactyl manus, no question
)) about it. If theropods got up on their hind legs to use their hands
)) for grasping, they had five fingers when they did so. The question is,
)) with a hand adapted for grasping, why did they lose the outer two or
)) three digits? The BCF answer is that the hand started to evolve into a
)) wing and lost its outer digits before the three-fingered theropods
)) descended from the trees.
)) 
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>Bipedality and forelimb reduction in theropods
        See Tom Holtz's recent post on "forelimb" reduction.  Personally, I
can't see why a bird would want *smaller* forelimbs, anyway.

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)) 
)) Whether the bird "wants" smaller forelimbs is not the issue. Whenever
)) ground-dwelling, flightless birds evolve, they >invariably< reduce the
)) relative size of their forelimbs. Every flightless bird from a penguin
)) to _Hesperornis_ to an ostrich to a kiwi to a _Phorusrhacos_ has small
)) forelimbs relative to body size, and especially when compared with
)) what size the forelimbs would have been, had they retained the
)) relative size of avian wings. This pattern extends naturally and
)) automatically to the earliest ground-dwelling, flightless birds,
)) namely, the theropods. Only in theropods, the wings still had claws
)) and still had a grasping function--and these anatomical characters and
)) functions exapted naturally into a highly predatory lifestyle.
)) 
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  As for bipedality, how many flying tetrapod forms are bipedal?
1+1/2 (I count pterosaurs as 1/2).  That's half of the total, not
counting the numerous quadrapedal gliders.  How many bipedal tetrapods
are flying?  1+1/2.  If my calculations are close, and I don't count
the aussie frilled-lizard, that's about 1/3rd of the total
(kangaroo-forms and primates and a half a pterodatcyl are the others).
You haven't yet proved this point.

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))
)) There are some 9000 species of flying bipeds alive today. If you're not
)) talking about these, I don't know what you're talking about.
))
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>Large size of theropods versus small size of birds
        Cope's Rule is a _generalization_, it is *not* a hard-and-fast rule!
one of the valid routes of selection is DWARFISM.  This may be difficult to
see in the fossil record, because homoplasy, paedomorphy, and allometric
considerations can mask the relationships, but there is certainly no
evidence that small animals *must* come from smaller animals.  Otherwise,
after a certain point, we might run out of small animals, and then we'd be
out of new animals.  God may play dice with the universe, but you don't have
to be omincient to avoid them odds!

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)) 
)) I wish someone had called it "Cope's Suggestion" rather than "Cope's
)) Rule." Of course I know about dwarfism, and there was even a time when
)) I imagined that theropods somehow underwent an extensive period of
)) dwarf evolution on their way to becoming birds. But I could not
)) imagine twenty million years of unmitigated island endemism or any
)) other factors that would last long enough for theropods to become
)) anything more than dwarf theropods, let alone evolve flight. So I came
)) around to the idea that dino-birds started out small and STAYED small
)) as they evolved into true birds. This, in turn, placed the theropods
)) in their Cope-correct, much more natural phyletic position as large,
)) ground-dwelling, flightless dino-bird descendants. It also gave the
)) dino-birds more time in which to evolve feathers, flight, etc., all
)) difficult evolutionary steps.
)) 
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>Hollow-boned and pneumaticized skeletons of theropods and primitive
>dinosaurs
        Could be simply related to bipedality.

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)) 
)) Hollow bones are a hallmark of many (though, of course, not all) tree-
)) dwelling and other acronomic vertebrates, from frogs (as Larry Martin
)) pointed out to me once) to birds. Hollow bones lighten a skeleton and
)) help the buoyancy of air to mitigate the effects of a fall. They are a
)) natural solution to the "falling problem" faced by all animals that
)) spend time high above the ground. People are bipedal, but they don't
)) have hollow bones, so the connection between bipedality and hollow
)) bones outside the avian groups is weak. Another example of _ad hoc_
)) patching of BADD theory.
)) 
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>Stiffened tail in theropods
        Balance, manoeverability [sic?], general predacious habits.

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))
)) In BCF, the stiffened tail of theropods is exapted from its original
)) use as an airfoil to help the falling arboreal archosaur to stabilize
)) itself during the fall and to direct itself to a safer landing place.
)) Later dino-birds used the tail as a true airfoil for stability during
)) long, unpowered glides.
))
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>Oversize manual and pedal unguals in theropods
        Huh?  You have got to be kidding?  That's like saying we *won't* win
a nuclear war because we have *more* missiles than anyone else!  Big
claws=big kills.  Period.

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)) 
)) We dino-fans are so accustomed to thinking of huge claws as being
)) "necessary" to predation that we forget how few mammalian predators have
)) them. The largest claws of mammalian predators, found on bears and large
)) felids, are small potatoes, speaking relatively, next to the claws of a
)) typical maniraptoran theropod. Don't forget that the unguals were them-
)) selves sheathed in keratin that substantially increased the size of the
)) claws over and above what we normally see in the fossils.
)) 
)) In BCF, the giant claws of theropods were exapted for a predatory
)) lifestyle from their humble origin as grasping organs for clinging to
)) trees: another solution to the falling problem. As Feduccia has
)) pointed out (no pun intended), oversize, sharply pointed, highly
)) curved claws characterize many tree-dwelling birds. Such claws are
)) observed in _Megalancosaurus_ and other drepanosaurids, and are a
)) prime reason for assuming arboreality in these forms.
)) 
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>Maniraptoran forelimbs of certain theropods
        When someone explains what this means to me, I'll be happier.  I'll
throw this one at you:  Why is it that those "certain theropods" seem to be
the ones that are the most birdlike.  If these dinobirds were constantly
spitting out new radiations, I would expect to see the maniraptoran wrist in
more than one group, and perhaps in other early forms.  Shouldn't
Lesothosaurus have one?

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))
)) _Lesothosaurus_ was an ornithischian not closely related to the
)) theropod lineage. It and other phytodinosaurs diverged from theropods
)) well before the appearance of the maniraptoran forelimb. As Paul
)) Sereno recently noted (he came to Buffalo this past weekend to lecture
)) on his dinosaur discoveries to the Buffalo Museum of Science, and we
)) had lunch together twice--he loves Buffalo chicken wings, one of the
)) few things this city is noted for), the maniraptoran forelimb occurred
)) in a wide range of theropods from allosaurids to chickens.
)) 
)) In BCF, the maniraptoran forelimb evolved as an improvement to a forelimb
)) already functioning as a primitive wing. The maniraptoran forelimb is
)) anatomically restricted in its ability to grasp and move--a sacrifice
)) evolutionarily selected for because it made the forelimb easier to flap--
)) a method of making the forelimb musculature more efficient for flying.
)) This forelimb and its "power stroke," or primitive wingbeat, were exapted
)) into a kind of killing stroke for predation in the flightless maniraptoran
)) theropods.
))
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>Retroverted hallux of most theropods
        Most?  I was not aware that it was in most.  I was aware that this
occurred in dromaeosaurids and not in troodontids, indet. in ornithomimids,
?in Oviraporoids, not in therizinosauroids, I haven't heard of it outside of
the coelurosaurs, but you're welcome to enlighten me.

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))
)) In the foot of theropods at or above the ceratosaurian grade, the
)) hallux articulates into a groove low down on the back of the second
)) metatarsal.  I call this position "retroverted." In BADD theory, the
)) first metatarsal is considered to have migrated to the back of the
)) foot, lost its proximal end, and become reduced in size all for the
)) vague reason that it was not needed in theropod locomotion. If it was
)) not needed, or if it hampered theropod locomotion, why did it not
)) >just shrink away<, as it did in ornithischians, and as the fifth
)) metatarsal did in almost all dinosaurs?  Why all the evolutionary
)) trouble of migrating to the back, losing its proximal end, and
)) becoming situated low down on the metatarsal arch instead of high up
)) near the tarsus?
)) 
)) In BCF, the hallux became retroverted as an adaptation to perching, as the
)) evolving wings started to lose their grasping and climbing function. When
)) the ground-dwelling form evolved, the retroverted hallux became vestigial,
)) since it was a hindrance to habitual bipedal locomotion. Its variable
)) fate in various theropod lineages supports the notion that the hallux
)) vestigialized separately in each lineage. Simple and natural solution to a
)) rather vexing problem for BADD theory.
))
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>Keeled sternum in theropods at and above the phyletic level of _Allosaurus_
        I presume you mean fully ossified keeled sternum, and the taxon you
mean is Coelurosauria. So birds developed earlier, but they didn't develop
the keeled sternum until later?.  As several folks have pointed out in the
Mononykus debate, a keeled sternum doesn't necessarily mean flight.  I'd
like one, myself.  In any case, all you've then proved is that coelurosaurs
are secondailyy flightless.

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))
)) Well, that's certainly something, isn't it? It's difficult to tell when
)) the keeled sternum appeared in the dino-bird lineage, because whenever the
)) wings reduce in flightless birds, the keeled sternum diminishes and
)) quickly vestigializes. My BCF guess is that a keeled sternum like those
)) of avialan birds did not appear until rather late in avian evolution, but
)) that some kind of mildly keeled sternum for the attachement of flight
)) musculature evolved somewhere around the point when the ceratosaurians
)) diverged. Here's where we really need to see more sterna.
))
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>Presence of a furcula in certain theropods
        I am sick of this argument, myself.  Some thecodonts may have had
these too.

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))
)) Yeah? Which thecodonts? The earliest known furcula (not counting the
)) questionable wishbone described by Sankar for _Protoavis_) occurs in
)) _Longisquama_, where it is a ringer for the furcula of _Archaeopteryx_ and
)) is the best single character for placing _Longisquama_ in Dinosauria.
))
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>Scarcity of pre-_Archaeopteryx_ "birds,"
        It's more parsimonious to presume there weren't any.

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))
)) I see! You're a >creationist<! You just wrote "there weren't any"
)) pre-_Archaeopteryx_ birds. So _Archaeopteryx_ had no precursors and
)) therefore arose by special creation. Or did I read you incorrectly? If
)) you're a creationist, it puts a whole new slant on your postings! Tell
)) me: If there were no pre-_Archaeopteryx_ birds, whence did the genus
)) arise?
))
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>and existence of all so-called "bird precursor" dinosaurs in strata
>>younger< than that of _Archaeopteryx_
        So the fact that there are echidnas today proves something about the
way mammals developed?  Let's be real, the raptors _were_ "The Nastiest
Dinosaurs."  If _I_ met one, I couldn't make it extinct! 

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))
)) BCF explains the existence of Cretaceous birdlike dinosaurs as relics
)) of their Triassic and Jurassic origins. So does BADD. But what hurts
)) BADD is that _Archaeopteryx_ is one of the oldest maniraptorans. If BADD
)) were correct, we should see lots of _Velociraptor_-like theropods in the
)) Jurassic, but we don't. Instead, we get _Ornitholestes_ and such. Birdlike
)) but much farther down the family tree than _Velociraptor_ and
)) _Deinonychus_.
))
)) In BCF, it takes time for the larger flightless forms to evolve from
)) the dino-birds. Today's ostriches and other ratites are among the most
)) primitive birds known. Their lineage diverged from modern birds back
)) in the Paleocene. Likewise, the dromaeosaurid lineage diverged
)) sometime way back in the Jurassic and became expressed as large,
)) ostrich-size forms only in the Cretaceous. We'll find dromaeosaur-like
)) forms in the Jurassic, but they will still be small, like
)) _Compsognathus_ (which I've claimed is at the base of
)) Tyrannosauria). Hence also my point about small theropod teeth in the
)) Morrison.
))
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>Microfossil theropod teeth in Jurassic strata
        Uh...  So there couldn't have just been small theropods like the
fifteen or so that have been found in the past decade?

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))
)) Which fifteen or so are these? I want names! Fifteen or so small, Late
)) Jurassic theropods, about 50 cm long from snout to tail-tip. Go for it!
))
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>Presence of feathers in birds versus apparent lack of feathers in
>most if not all theropods
        _Apparent_ lack of evidence, indeed.  Since there haven't been any
published accounts of skin impressions on small dinosaurs other than
Archaeopteryx and birds yet, I think you are, in fact, quite wrong in your
assertion that there is something in need of explanation here.  We have two
cases of feathered small theropods (Archy and Confusci), one ?pitted?
dromaeosaur skin, and whatevertheheck Pelicanomimus has, versus no scaley
small theropods.

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))
)) John Ostrom published a description of _Compsognathus_ in which he found
)) no trace of flight or contour feathers, despite the fact that the speci-
)) men came from the same lithographic limestone that _Archaeopteryx_ is
)) found in, which preserves feather impressions very well, particularly
)) in nearly complete specimens. If dinosaurs like _Compsognathus_ were
)) ancestral or closely related to birds, one would expect to find traces
)) of those dermal structures that evolved into feathers. BUT--if
)) _Compsognathus_ had secondarily lost its feathers, this could explain
)) Ostrom's inability to find them. To paraphrase Sherlock Holmes, sometimes
)) we have to explain why the dog >doesn't< bark.
))
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And don't forget:
THAT WHICH MAKETH THE DINOSAUR IS A DINOSAUR
        If your "dinobirds" exist, after a certain point, they _are_
dinosaurs.  I think it's a pretty simple calculation to see that modern
birds probably branched off of a BCF tree after some other dinosaurs.

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))
)) Right. The flightless, ground-dwelling dino-birds ARE the dinosaurs.
)) Modern birds are the crown group of the dino-bird clade.
))
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>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.
        And BCF is an interesting hypothesis.  Whenever I get new data, I
test it against BCF as a control.  BCF has some stuff going for it, at least
as far as theropods are concerned.  I really wouldn't be surprised if
someday someone is able to make a convincing case (not that Greg Paul isn't
already trying) that some theropods were secondarily flightless.

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))
)) As I see it, I've already done this. Now it's up to everyone else to
)) come around.
))
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