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MORE BCF FAULTS



I sense a real quick death of this thread so I am going to try to get my 
last word in before this thread disappears.

<<This is of course not an issue of respect but of building a theory of 
dinosaur phylogeny and the origin of avian flight. Certainly, BCF has 
weaknesses, but I think the currently accepted "standard model," which I 
have playfully called the BADD theory (for "birds are dinosaur 
descendants"), presently suffers from more. Indeed, the closer BADD 
comes to BCF--and it has recently moved slightly in that direction, with 
the discovery of feathered theropods such as _Caudipteryx_ and 
_Protarchaeopteryx_ and having to consider the possibility that these 
were secondarily flightless theropods--the fewer weaknesses it will have 
(heh heh).>>

My main problem with BCF is its occasional (sometimes persistent) 
releance on speculation as a real evidence.  The problems with BAMM 
(Birds Are Modified Maniraptorans; I like this term better, even though 
I find the use of acronyms somewhat silly) are typical problems in 
reconstructing (ecological) phylogeny.  

<<BCF synthesizes the BADD model, in which birds acquire the ability to 
fly as ground-dwelling, cursorial dinosaurs, with the "trees-down" 
model, in which birds acquire the ability to fly as arboreal archosaurs 
unrelated to dinosaurs. I simply show how birds might have originated as 
arboreal archosaurs that gave rise to dinosaurs, thereby explaining the 
close relationship between birds and theropods evidenced by their 
anatomical similarities. Everything else is details.>>

There is by no means a consensus on whether birds evolved from cursorial 
animals.  The opinion in paleontological circles certainly is a 
majority, more by default than anything else.  There is a growing group 
of paleontologists who are believing that flight evolved from the trees.  

Again, one of the main faults of your theory is it relies that there 
were arboreal archosaurs that gave rise to dinosaurs.  I cannot find any 
arboreal features in the first dinosaurs.  I can find arboreal features 
in pterosaurs, which evolved from prolacertiform archosauromorphs or 
lepidosauromorphs.  

<<_Mononykus_ may or may not be "within Aves far above the level of 
Archaeopteryx." (I happen to think not: the tail of _Mononykus_, if 
correctly restored, is far too grave a reversal to the theropod 
condition for _Mononykus_ ever to have been an avialan bird; nor are its 
arctometatarsalian feet in any way avialan. Its birdlike cranial anatomy 
is quite likely the result of convergence from having to accommodate a 
perhaps independently enlarged braincase. I may change my mind on this, 
however, once I read the new description of the _Mononykus_ skull.) This 
doesn't change the essence of my remark, namely, that secondary 
flightlessness has been shown to yield a very theropod-like animal>>.

Are you suggesting that prokinesis in Mononykus evolved to accomodate an 
enlarged braincase?  From all that I have seen of the caudal half of 
Mononykus I find no reason why this could not have evolved from an 
Archaeopteryx-like tail.  Mononykus has a more robust tail but this is 
not at all uncommon in birds.  Pici and Coliiformes have large 
transverse processes to support pygostylar feathers where most other 
birds do not (particulary Sandcoleiformes, the postulated closest 
relatives of Pici (excluding Galbulae) and Coliiformes (or Coliidae).  
Of course secondary flightlessness will yield a theropod-like bird, but 
the problem is that we cannot say that the most parsimonous hypothesis 
is that various theropods lost powered flight or otherwise.  

<<Well, as far as I can tell, evidence from physics truly >falsifies< 
the idea that birds evolved the ability to fly from the ground up. As 
far as I'm concerned, it is 100%, no question disproved, even if a few 
diehards haven't yet come around to thinking so. Therefore, at some 
point in the evolution of avian flight, well before the appearance of 
_Archaeopteryx_, birds >must< have gone up into the trees. So any 
ground-dwelling, cursorial descendants of those flying, arboreal 
pre-archaeopterygids would, by my definition, be >secondarily< 
flightless. There remains the problem of what we mean by "flying" with 
regard to bird evolution, but I've been pretty clear about this in 
previous posts. The dictionary defines "flight" as "passage through the 
air," so if leaping from branch to branch, falling, parachuting, and 
gliding were among the features of an arboreal lifestyle in 
pre-archaeopterygid dinobirds, then they were technically fliers in my 
book, and their descendants were secondarily flightless.>>

I agree here that conventional aerodynamics and physics certainly makes 
the cursorial theory untenable (assuming we ignore Rayner's wind gliding 
model; a model that assumes good control of the body in conditions where 
most birds have their troubles).  Of course the ancestors of 
Archaeopteryx may have lived in the trees before the level of 
Archaeopteryx (most arboreal proponents support this), but you do not 
call the ancestors of Archaeopteryx birds unless they show evidence of 
being within Aves.  

I am not aware of any gliding animals that "lost" their flight.  This is 
not to say that it did not happen, but the descendents should show 
characteristics of gliders or parachuters.  

<<I have been through this argument many times, but it is worth 
repeating here. Surely you don't think that _Archaeopteryx_ was the 
>only< flying, feathered creature of the Late Jurassic? Surely you don't 
think that _Archaeopteryx_ sprang into existence with no evolutionary 
relatives or forebears, even though the fossil record has currently 
presented us with no >physical< remains? Surely you don't think, just 
because we have only eight _Archaeopteryx_ specimens, that the entire 
population of _Archaeopteryx_ at Solnhofen in the Late Jurassic was less 
than millions? Regarding _Protoavis_, as Larry Witmer notes in the 
introduction to Chatterjee's book, if even >one bone< in the _Protoavis_ 
assemblage is avian, it shows that there were Triassic birds. Are you 
prepared to state that >none< of the _Protoavis_ bones is avian? 
_Archaeopteryx_ and birds arose from >something<, and in BCF the same 
something (or somethings) also gave rise to theropod dinosaurs.>>

I don't think that Archaeopteryx was the only flying creature of the 
Late Jurassic, the Korean bird certainly proves that, but we cannot say 
that birds originated anytime other than the Middle to Late Jurassic 
because we find their ancestors in the rocks and there is no evidence of 
pre-Late Jurassic birds.  I say that Archaeopteryx came from 
maniraptoran dinosaurs that developed an arboreal lifestyle, the steps 
were rather simple.  Archaeopteryx may have came from another bird or 
birdlike creature, but this does not prove that there was a vast, 
diverse race of 'dino/birds' hopping around in the trees from the Middle 
Triassic to the Late Jurassic.  

The entire Archaeopteryx population may have been rather small, though, 
assuming that it was a trunk-climber in a sparsrely forested archipelgo.  
I do agree with Witmer's statement very much, but I still cannot find a 
single bone in the Protoavis assemblage that can unequivocably be called 
an avian bone.  I still go by Zhou (1995) who says that a dinosaur with 
certain habits can begin to look like a bird.  Of course the paper was 
not really top notch, but it does go to show you how a theropod can, 
through bizarre behaviors, can look like a bird.  

<<Once we uncover real representatives of those groups, we will have a 
much firmer idea of the >details< of the evolution of birds and avian 
flight. I eagerly await their discovery, because this will constrain the 
BCF model. Right now, I have faith that they won't >disprove< the BCF 
model, but you never know, of course.>>

It certainly does constrain the BCF model because as of now, it is 
mostly hypothetical.  

In regard to Longisquama, Megalancosaurus, and Cosesaurus, G.O. wrote: 

<<I never thought that these formed a natural group (clade); 
Basitheropoda was a paraphyletic taxon when I proposed it in 1991. 
Rather, each of these genera represents a side branch of arboreal 
archosaurs (or perhaps archosauriforms), Their mere >existence< supports 
and justifies the idea that there could well have been >other< arboreal 
archosaurs, presently unknown, that gave rise to birds (and 
dinosaurs).>>

That makes little sense.  Because there were arboreal archosaur-like 
animals living at a certain time, means that there may have been a big 
race of other arboreal archosaurs.  This is rather like saying that 
since there are lizards like *Draco* today that have a pleural gliding 
membrane, there must be other lizards like that today.  Again, you are 
finding "evidence" where there is just speculation.  

<<Prolacertiforms are the closest diapsids to archosaurs, so it is not 
surprising to find prolacertiform characters in _Megalancosaurus_ and 
_Cosesaurus_, both of which I consider to be below Dinosauria in the 
archosaur cladogram. Exactly where these animals fall--whether they're 
closer to archosaurs than to prolacertiforms or vice versa--is not 
particularly relevant to the BCF thesis. They're such charming animals 
that I'll expand my list of archosaur taxa in _Mesozoic Meanderings_ #2 
to include prolacertiforms, if it turns out that basitheropods and 
pterosaurs are prolacertiforms instead of archosaurs.>>

Prolacertiforms are also considered to be in the Lepidosauromorpha, but 
I agree that they are close to mainstream archosaurs.  In most 
cladograms, Megalancosaurus is ranked with the protorosaurs, near basal 
prolacertiform.   

<<Here I disagree. The presence of a furcula, together with a wide-open 
antorbital fenestra and dermal structures that strongly resemble 
feathers (without actually being feathers), strongly supports placement 
of _Longisquama_ in the archosaur cladogram as a primitive 
theropodomorph dinosaur. This will be confirmed (I predict) when a 
complete _Longisquama_ is discovered. Right now, the type specimen--the 
only existing specimen with skeletal parts--includes only the 
forequarters: skull, neck, shoulders, forelimbs, and the anterior rib 
cage. We need to see the pelvis, hindlimb, feet, and tail before we can 
confidently exclude _Longisquama_ fro >Dinosauria. And even if 
_Longisquama_ turns out to be not a dinosaur but an animal that acquired 
a few dinosaurian features independently outside Dinosauria, this 
doesn't damage BCF. It just means we have a longer wait for a Triassic 
dinobird to be described.>>

Excuse me while I go and regroup tritylodontids in the Multitubercula 
because of their similiar dentitions and orthal movements.  Your logic 
makes no sense because it does not account for convergence and makes 
speculations where there is no evidence.  Using your logic, gliding 
membranes in flying lemurs and flying squirrels is evidence of common 
ancestry and Confuciusornis is a neornithine bird because it lacks 
teeth.  

<<Yes, well, if you exclude >all< the characters that they share with 
archosaurs, of course "they share nothing at all" with them! Small, 
arboreal tetrapods, whatever their affinities, are >extremely< rare as 
fossils. The fact that _Cosesaurus_, _Megalancosaurus_, and 
_Longisquama_ specimens exist at all is incredible. The fact that 
they're all so different from one another indicates how diverse the 
arboreal archosauriforms (or basitheropods) were: Try to imagine the 
possible ancestors or close relatives of megalancosaurids--wherever you 
might classify them--or of _Longisquama_. As I said once before, surely 
you don't think these were the >only< arboreal archosauriforms that 
existed during the Triassic, that they arose spontaneously with no 
relatives or forebears or descendants?>>

Lest us not forget that they also share a fused astralagus and calcaneum 
like lepidosauromorphs.  The features that they share with archosaurs 
are simply primitive within their group, the Prolacertiformes, they do 
not show any features that indicate that these two animals are more 
closely related to each other than anyother prolacertiforms.  It does 
not matter that they were the only arboreal near-archosaurs in the 
Triassic, we still have not found any evidence for the supposed arboreal 
forebearers of the dinosaurs.

<<As long as the animal uses all four limbs for climbing, the 
pamprodactyl foot >might< be more useful (who can speculate on the 
relative "usefulness" of foot anatomy; how would you measure 
"usefulness"?); but once the forelimbs are generally lost to climbing 
and become wings, the hind foot must assume most if not all of the 
climbing function, and then I think the shoe is on the other foot 
(brutal pun here). Then I think an opposable hallux becomes much more 
"useful." Certainly an opposable hallux occurs in many, many modern 
arboreal birds; this alone speaks volumes about the "usefulness" of the 
structure.>>

The anisodactyl foot probably evolved for perching, as suggested 
(tenatively) by Bock and Miller.  

<<NOTE: The BADD model >cannot< account for this exact pattern of manual 
digital loss in ground- dwelling cursorial bipeds, which presumably 
would find retaining all five digits more "useful" for grasping and 
holding prey (since they were not converting their forelimbs into 
wings). BADD gives >no functional reason< for the loss of manual digits 
IV and V; this is just >something that happened,< ad hoc, that turned 
out to be "useful" when the forelimbs were suddenly exapted for 
flight.>>

Really, I always thought that they lost their digits in that pattern for 
grasping.  

<<BADD fails to answer the question of why manual digital loss in 
theropods occurred at all, let alone in such a specifically asymmetric 
way.>>

That doesn't mean that there will be an answer or was an answer.  And I 
always thought that there was, release of functionalless digits for 
grasping prey.  

<<Asymmetry of limb elements in tetrapods often stems from adaptation to 
flight. Airfoils must be asymmetric, because it is the difference 
between the airflow over the top and bottom surfaces that provides the 
lift; a symmetric wing would have the same kind of airflow over top and 
bottom and thus generate near-zero lift. Wing asymmetry occurs 
everywhere in the wing: in the feathers themselves as well as in the 
shapes and arrangement of the skeletal elements. Theropods had highly 
asymmetric hands, thicker at the "leading" edge (digit I), thinner at 
the trailing edge (digits III-V, with IV and V vestigialized or 
nonexistent), and BCF accounts for this in a perfectly natural manner. 
The BADD model, in which the forelimbs must preacquire their asymmetry 
for some reason unrelated to flight, has tremendous difficulty 
explaining it.>>

James Cunningham nicely demoloshed this.  

<<Exaptations are not miracles, neither in BCF nor in any other 
evolutionary theory. Feathers, perhaps acquired for sulfate excretion, 
become exapted for insulation, display, flight, you name it, in BCF and 
in BADD. A >miracle< would be the accumulation of twenty or thirty avian 
characters for twenty or thirty different reasons other than for flying, 
only to find that this particular combination of twenty or thirty 
characters enabled the animal to fly. How can adaptations to a cursorial 
lifestyle suddenly also be perfectly suited for a volant lifestyle? If 
you want to have a whale evolve from mesonychid carnivores, you put them 
in the water >first<; they don't evolve flippers and >then< go into the 
water! Likewise with birds: Put them in the air, or at least, up in the 
trees, >first<. Then let them evolve all their adaptations for flying. 
Why is this not perfectly obvious??>>

You're sounding a bit like Fred Hoyle and his main anti-evolutionist 
statement: "Evolution is akin to a whirlwind blowing through a scrapyard 
and ending up with a Boeing 747".  I can't count 20 or 30 characters 
anyway.  

Arboreal adaptations can be useful for the evolution of flight.  Of 
course, bipedally had to evolve first (and not for arboreality because a 
bipedal arboreal animal is not balanced unless it is bipedal beforehand) 
and release of the forelimbs.  

<<You misunderstand my definition of a miracle. To me, a miracle would 
be the spontaneous boiling of a cup of water because all the water 
molecules happened, by chance, to align their thermal motions for a 
measurable interval of time. This is the same kind of miracle, though 
actually far less likely (because there are lots more molecules in a cup 
of water than anatomical features in a tetrapod skeleton), as the kind 
BADD wants us to accept: that twenty or thirty anatomical features, 
unrelated to flying, accumulate in a single animal ("align themselves") 
and thus allow it to fly. I am not calling exaptations miracles; I am 
calling the serial alignment of twenty or thirty unrelated exaptations a 
miracle.>>

"Evolution is akin to a whirlwind blowing through a scrapyard and ending 
up with a Boeing 747".  You're sounding more like Fred Hoyle. Evolution 
works this way in many cases.  


<<It could well be the easiest route to flightlessness in fully volant, 
ornithoptering birds. But there is no reason to state that it is the 
>only< way for flightlessness to evolve. This is unfounded dogma, plain 
and simple, for which you have no support from the fossil record. 
Certain features of ratite birds are paedomorphic, but other features 
are peramorphic, and still others are neither. If paedomorphosis were 
the >exclusive< means of acquiring flightlessness, then ratite birds 
would >exactly< resemble giant chicks--and of course they do not. Ratite 
hind limbs are certainly not paedomorphic, for example, and neither were 
theropod hind limbs. Indeed, I can't quite grasp the relevance of your 
comments concerning paedomorphosis, both here and in previous posts, to 
BCF.>>

Since paedomorphosis is the consistent factor that causes the lack of 
flight in birds, we can assume this for theropods.  And since theropods 
lack paedomorphic features, I find it unlikely that they were 
secondarily flightless (I say the same thing for the known phylogeny of 
theropods, which does not support secondary flightlessness regardless of 
paedomorphic features).  Ratites do have paedomorphic hindlimbs that 
were disproportionally robust.  

This is probably the last word I am going to say on this issue, unless 
another post comes up with some *valid* counterpoints.

Matt Troutman

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