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BCF (was Ruben's new paper)





Some of us who have been on the DML for a while would remember a fellow named 
George Olshevsky who came up with a rather unorthodox 'hypothesis' for the 
origin of avian flight called 'BCF' ("birds came first").  BCF isn't really a 
hypothesis, more a combination of assumptions, assertions, and outdated 
concepts.  In these respects, BCF parallels some of the comments made about the 
recent Ruben paper.  Anyway, back in the day, Olshevksy pushed BCF rather 
aggressively, although he has been relatively quiet recently.  I had forgotten 
about BCF until, out of the blue, Darren Naish offered a commentary of BCF on 
his blog, including a direct refutation...

http://scienceblogs.com/tetrapodzoology/2009/06/birds_come_first_hypothesis.php

http://scienceblogs.com/tetrapodzoology/2009/06/birds_come_first_no_they_dont.php

It's timely, because two of the pillars of the Birds-Are-Not-Dinosaurs (BABD) 
argument are also embedded in BCF.

Firstly, the 'temporal paradox' which alleges that the purported ancestors of 
birds occur later than the first birds.  Not only does this erroneously 
conflate the concept of "ancestor" with "sister taxon", but it also ignores 
fossil evidence for non-avian paravians that are roughly contemporary with 
_Archaeopteryx_.  Both these have been aired already in the discussion of the 
Ruben paper.

Secondly, the BAND camp subscribes to the same typological ideas about what a 
"bird" and a "dinosaur" actually are.  "Never the twain shall be" summarizes 
this outdated perception really well.  This conceptualizes birds as highly 
advanced physiologically, and dinosaurs (as reptiles) as irreconcilably 
primitive by comparison.  [Using a reconstruction of _Tyrannosaurus_ taken from 
Osborn (1916) is symptomatic of this typological mindset.] 

Being wedded to highly dichotomous views about what dinosaurs and birds are (or 
rather *should* be), it is therefore only a short step to making assumptions 
and assertions about what the evolutionary process that led to bird flight 
*should* be.  This guiding principle is far more of a problem for BAND than 
BCF, with BCF at least recognizing that the anatomical characters common to 
birds and (non-avian) dinosaurs are the products of transformational change.  
However, BCF falls into the same typological trap by erecting an _a priori_ 
scenario of how avian flight *should* have evolved, and then trying to shoehorn 
the available evidence into it.  

The current, highly favored approach (non-BAND/BCF), on the other hand, 
constructs a phylogenetic framework based on available taxa, and then comes up 
with ecological, morphological, physiological, or even biogeographical 
hypotheses that can account for the sequence of character acquisitions (or 
losses).  One of the advantages of this approach is that it allows room for 
exaptation, because it does not tie specific characters to specific behaviors.  
Personally, even though I'm skeptical of some exaptive hypotheses (e.g., 
predatory stroke --> flight stroke), I find it difficult to believe that 
*every* flight-related character found in modern birds originally evolved for 
flight.



Cheers

Tim