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BCF& COMMENTS ON IT



Let me point out that I mean no disrespect to George Olshevsky or any of 
the BCF proponents, this message is simply to point out some weaknesses 
or flaws of BCF and the BCF scenario.  

George Olshevsky wrote regarding secondary flightlessness:

<<All the cladograms I've seen do indeed support secondary 
flightlessness in _Mononykus_, certainly. But the important thing is 
that, at this point, secondary flightlessness for many theropods is not 
>falsified< by any cladograms. There's a big difference between "not 
supported" and "falsified." Secondary flightlessness occurred repeatedly 
among Cretaceous birds (hesperornithans, _Patagopteryx_, _Gargantuavis_) 
and Cenozoic birds, and there's no reason believe that the process 
didn't also occur within Triassic and Jurassic birds groups, such as 
they were.>>

But these cladograms also support that Mononykus is within Aves far 
above the level of Archaeopteryx.  I like John Hutchinson's idea that 
alvarezosaurs are closest to the ornithurines even though I have not 
seen any evidence that this is true other than the large braincase and 
foramen magnum.  It is true that there is a difference between "not 
supported" and "falsified", and so far the evidence does not support 
secondarily flightless NON-AVIAN dinosaurs.  However, just because the 
evidence at the time does not *fully* falsifiy the secondarily 
flightless hypothesis does not mean that one can scientifically justify 
supporting this hypothesis because it is not fully, 100% disproven.  

What Triassic and Jurassic bird groups?  If you're referring to 
Protoavis as a representative of one of these phantom groups I may be 
able to understand, but I would have to say that Protoavis is of 
doubtful "origins", the braincase looks almost crocodylomorph or 
coelurosaurian and besides the heterocoelus vertebrae and the large 
renal fossae the rest of the skeleton is questionable.  Of course 
Chatterjee may be right in his interpretations but this does not fully 
prove avian status or even the presense of volant capability.  Zhou 
(1995) has commented that a dinosaur of strange habits can begin to look 
vaguely birdlike in some characters.  

Regardless, these bird groups are for the most part purely speculative 
and cannot be taken as actual evidence (even though they sometimes 
appear to be sometimes).  Or maybe you're referring to those 
'dino/birds' such as Megalancosaurus, Cosesaurus and Longisquama.  NO 
evidence points to whether or not these are a natural group or not.  The 
evidence shows that Megalancosaurus and Cosesaurus are Prolacertiformes 
and that Cosesaurus is one of the closest animals to the Pterosauria 
(this is Dave Peters' hypothesis, the alternative hypothesis is 
virtually identical except they are not near pterosaurs).  Longisquama 
cannot be placed ANYWHERE, it cannot be put into the Diaspida 
confidently (Padian).  What do all these animals share?  Well, other 
than the fact that all have been put forth as a possible ancestor to 
birds and all share a possible arboreal lifestyle, they share nothing at 
all.  Sure they do have some characters such as triangular skulls; 
unserrated, isodont teeth (Megalancosaurus); a birdlike shoulder girdle 
(this is found in Cosesaurus, a relative of pterosaurs, which have a 
birdlike shoulder; a strap-like scapula is seen in Megalancosaurus); and 
feathers (Longisquama) that might link these disparate animals together 
by default as possible ancestors of birds or birdlike creatures (phantom 
Triassic and Jurassic "bird" groups; the elusive and totally 
hypothetical 'dino/birds' that gave rise to the various groups of 
dinosaurs).  However, this would be akin to linking placental American 
flying squirrels to marsupial sugar gliders because they share a rounded 
skull; large round eyes; a gliding membrane; and similiar proportions of 
the forelimbs and hindlimbs.  

FINGERS

BCF predicts that if there were a variety flying forms there could be a 
variety of finger numbers (1-2-3; 2-3-4; or didactyl).  The basis of 
this is that reduction of fingers can provide a better leading edge of 
the wing for flight or gliding.  However, again this is purely 
speculative and there is no fossil evidence in support of an idea like 
this.  Embryology studies aside, there is no evidence that the 
enantiornithines, Archaeopteryx, and theropod dinosaurs had digits 1-2-3 
and ornithurine birds had digits 2-3-4.  All the available evidence, 
including Burke and Feduccia's paper, which does not provide any new 
information into the dinosaur finger debate other than that the digit 
opposite the ulna is the primary axis of cartilage condensation (digit 
IV in most tetrapods, digit III in theropods and presumeably birds), 
supports that the sauriurines (Archaeopteryx+enantiornithines) and the 
ornithurines had the same digits.  Didactyl in Compsognathus and 
tyrannosaurs does not necessarily mean that they had a common ancestor 
just as it does not mean that cuculiforms and picines hada common 
ancestor because they had a similiar, but totally convergent, according 
to all analyses starting with Bock and Miller (a non-cladistic analysis 
in 1959), zygodactyl foot. 

And while on the subject of the zygodactyl foot, let me point out that 
the zygodactyl foot did not evolve for scansorial clinging as is 
commonly stated (most notably in Pat Shipman's recent book).  The 
zygodactyl foot evolved for perching according to Bock and Miller, and 
it is the ectropodactyl foot (zygodactyl in rest and perching, but 
during climbing the hallux is usually useless and digit IV deviates 
strongly laterally; seen in many woodpeckers).  A reversible digit I is 
not needed for climbing, pamprodactyl (all digits anterior) is by far 
the best scansorial foot and incidently it is found premanufactured in 
dinosaurs.  

LOSS OF DIGITS

Loss of digits does not necesarily indicate arboreal habits whether in 
the actual animal or in the ancestor of the animal.  Try to tell an 
equine that its ancestors were arboreal and that is why it lost its 
digits. True, loss of digits, either manual or pedal, can be indicative 
that the animal is question came from arboreal descent or is arboreal.  
As I noted above, the hallux is frequently unused in ectropodactyl 
climbers because the extremely mobile digit IV compensates for the usual 
function of the hallux.  Digit IV, when laterally directed, resists the 
the force C, which is the force pulling the bird away from the trunk 
(there is one main force of gravity that pulls a clinging bird down, A.  
A is divided into forces B and C.  B is the inwardly  and downwardly 
pulling force.  C is the outwardly pulling force).  Any digit or 
appendage that does not support counterbalance any force acting on the 
bird is useless, in this case it is the hallux.  The lesson that this 
teaches us is that the manual digits in theropod dinosaurs probably were 
not lost due to climbing.  You see, if all were directed forward (and 
even if manual digit I was a "twist thumb" in the Bakkerian sense) then 
there would be no reason that any digits would be lost because they 
would still function like the digits II and III of an ectropodactyl 
foot, which counterbalance force B, the downward and inward force.  
Assuming that the totally hypothetical "typical" 'dino/bird' had five 
manual digits, and a possible laterally directing digit I, the other 
four digits, II, III, IV, and V, would still be functional for 
counterbalancing the force of B and perhaps even the overall downward 
force, A.  I hope that everybody understands this because without 
illustrations it is hard to understand.  The main point is that in the 
totally hypothetical "typical" 'dino/bird', ALL digits of the manus 
would be of use.  For a diagram of something similiar to this look at 
Chatterjee 1998 or better yet, look at Bock and Miller 1959.  The 
Scansorial Foot of the Woodpeckers, with Comments on the Evolution of 
Perching and Climbing Feet in Birds.  American Museum Novitates Num. 
1931.   

Since climbing is not an acceptable reason for the elusive, totally 
hypothetical 'dino/bird' ancestors of theropods there are other 
explanations for the loss of manual digits such as predation/grasping , 
lack of use of the digits, or even a better trailing edge for a gliding 
wing (this too is rather unlikely because the two digits lost would 
still have to support the feathers.  All of these answers are likely and 
not one can be held as absolute proof of BCF or any alternative 
hypothesis.  

MIRACLES

One part of the BCF scenario is that there are no "miracles" within it.  
In normal theropod phylogeny bipedalism was gained, partial  decoupling 
of the forelimbs, and then a forelimb stroke that evolved either for 
predation or other means that turned into the flight stroke.  It has 
been quiped that excepting this would be akin to accepting miracles.  
Dinogeorge finds it more likely that flight evolved from creatures 
without the help of "miracles" (most others call them exaptations).  
Going by the definition of miracle given, I can sight MANY. MANY, MANY 
instances within accepted (and virtually proven) parts of avian 
evolution that can be defined as "miracles".  The evolution of the 
reversed hallux and the anisodactyl foot through perching which then got 
exapted for downward tree-creeping in nuthatches.  The evolution of the 
zygodactyl foot for perching and then the evolution of lateral movement 
in digit IV during climbing making the ectropodactyl foot for scansorial 
climbing that became the modified pamprodactyl foot of the extinct 
ivory-billed woodpecker.  The evolution of a keratinous sheath over the 
mandibles, loss of teeth, evolution of a beak and the adaptive radiation 
of the varieties of bird beaks such as the finch bill, the hawk bill, 
and the flamingo bill. And so on, and so on, and so on.  Under the 
definition of "miracle" given by G.O., these can be considered miracles 
unless there are problems with these well established, tested and proven 
sequences. 

The "miraculous" evolution of features that led to flight in theropods 
are what most all call exaptations.  

USE OF FORELIMBS "AFTER FLIGHT"

One main part of the BCF theory is that after flight (parachuting, 
gliding, powered flight) the forelimbs of an animal would turn back to 
normal because they lack the specializations that modern bird forelimbs 
do.  Of course again, there is no evidence that theropods are derived 
from "flying", totally conjectural 'dino/birds'.  And really, there is 
no evidence that the theropods came from flighted ancestors; I cannot 
think of one instance where a gliding animal lost its "flight", so it is 
purely conjectural to assume what will happen once this happens.  In 
volant, powered flying ancestors the forelimbs are usually useless, 
probably due to paedomorphosis.  I'm sure you all remember what 
paedomorphosis is, and I still consider it the only factor that causes 
teresstrial flightlessness.  Hypermorphosis was put forth as a flight 
losing feature by Darren Naish, but ratites hardly seem overdeveloped in 
maturity (of course, neither did their ancestors to an extent, but not 
to the extent of modern ratites) and all of the features given as 
hypermorphic features are better described as paedomorphic features and 
some do not contradict the paedomorphosis argument (such as the 
well-developed aftershaft of ratites, many juvenile birds like the 
hoatzin have well-developed aftershafts).  Of course, that's just my 
humble opinion, feel free to contradict me.  Anyway, back to forelimbs.  
Phorusrhacoids are the only birds with fully functional forelimbs 
throughout life, but their forelimbs were modified to a point not seen 
in any theropod.  So there!

FINALE

I have a lot more to say but I'll quit here.  As I have said before, I 
mean no disrespect to anybody mentioned above, I simply am pointing out 
the flaws of BCF.  I do subscribe to some of the points of BCF (birds 
came from arboreal ancestors) but a good portion of it.  I think I have 
said enough for now.

Regards,

Matt Troutman 

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