[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

MORE ON BCF



<<Birds--that is to say, extant modern birds and their Cenozoic
predecessors--are indeed modified maniraptorans, according to both BCF 
and the "standard model." The already available evidence is too good for 
this not to be the case.>>

Wow!  An agreement ;-)

<<Where the "standard model" and BCF diverge is at the beginnings of 
flight. BCF contends that the Triassic and pre-archaeopterygid Jurassic 
ancestors of birds were far more birdlike in their arboreal lifestyle 
and ability to fly--that is, to control their passage through the 
air--than the "standard model" says.>>

Of course, there is little to no fossil evidence of this taking place.  

<<According to the "standard model," the Triassic and Jurassic 
bird-ancestors were ground-dwelling, bipedal theropods; according to 
BCF, the known ground-dwelling, bipedal theropods were secondarily 
flightless descendants of the smaller, more birdlike, quadrupedal, 
arboreal climbers and fliers that eventually evolved into birds.>>

According to the standard model, Triassic bird-ancestors were 
ground-dwelling, bipedal theropods, but Jurassic bird ancestors 
(ur-dromaeosaurs; proto-dromaeosaurs; etc.) may have been smaller, more 
birdlike, (faculatively) quadrapedal when climbing, arboreal climbers 
and parachuters/gliders that evolved into birds.  (Of course, this is 
according to Chatterjee and tenatively Witmer, plus a few others, but 
not to Ostrom, Padian, Chiappe, and Gautheir). 

<<In BCF, certain small, primitive archosaurs adopted an arboreal 
lifestyle, perhaps to escape ground-dwelling predators or just to push 
their habitat envelope, and stayed arboreal, becoming ever better 
climbers and, eventually, fliers.>>

Evidence for this, anybody?  I support this model for maniraptorans and 
possibly most maniraptoriforms, but the whole Theropoda? 

<<From time to time, a lineage of these arboreal archosaurs returned to 
a ground-dwelling existence and diversified into what we know as a group 
of theropods.>> 

I nearly forgot, but the badger and wolverine branch of the Carnivora 
(the name slips my tongue) has undergone something similiar to this.  As 
well as the phalengeroid Thylacoleo.    

<<In BCF, such theropod characteristics as short forelimbs and 
obligatory bipedal stance occurred repeatedly in each lineage because 
the forelimbs had become too winglike--or at least, too strongly adapted 
for climbing and leaping in trees--for use in walking (much like human 
forelimbs and bipedality). And so on.>>

Of course, this did not happen to badgers, did it?  And again, evidence? 

<<Testing BCF against the "standard model" in real terms will commence 
with the discovery of good specimens of very small theropods from the 
Triassic and Jurassic. Some, at least, will have long, winglike 
forelimbs if BCF is right, none if the "standard model" is right.>>

I cannot find any problem with finding small theropod dinosaurs with 
winglike forelimbs in the Jurassic, but there still is no evidence for 
something like this actually taking place.  Even if we do find a race of 
arboreal dinosaurs, it does not mean that that is proof of BCF.  Their 
relationship to other theropods has to be shown.  

Matt Troutman

______________________________________________________
Get Your Private, Free Email at http://www.hotmail.com