Re: New alvarezsaurid

[Dinogeorge <Dinogeorge@aol.com>]

In a message dated 98-03-26 11:22:06 EST, martz@holly.ColoState.EDU writes:

<< I didn't say it was a ridiculous idea; but I don't see how you can
 discard the idea that the tridactyl manus evolved for predation as
 untestable speculation, and then turn around and say how BCF solves the
 problem of the tridactyl manus with equally unsubstantiated
 flying-preening-whatever models for the development of the same feature.  
 Its an idea, but it does not give more weight to BCF then the predation
 idea gives to "BADD" if both are purely speculative. >>

Exactly so. This is why I have decided not to argue for BCF and against BADD
on the grounds that the observed anatomical changes in the theropod-bird clade
represent "improvements" to flight, predation, or anything like that. We have
no idea >why< any anatomical changes occurred, only that they did occur, and
anything further is simply pointless rank speculation. My argument against
BADD is that it requires me to agree that the evolution of flight is a
"miracle," something like changing water into wine: we have large (25 kg or
more), cursorial animals with relatively puny forelimbs randomly accumulating
the numerous characters seen in flying birds until, suddenly, a flying bird
assembles itself. My argument against the birds-are-not-dinosaurs stance of
certain ornithologists is quite similar: that the >same< set of characters
accumulates not just once but >twice<, in two separate clades, leading on the
one hand to flying birds and on the other to ground-dwelling theropod
dinosaurs. That position seems like "double miracle" to me.

In BCF, I simply claim that the characters of flying birds accumulated over
the course of their evolution from nonflying to flying animals (>why< these
particular characters appeared is not presently knowable), and that theropod
dinosaurs retained these characters as holdovers from avian evolution in
lineages that diverged from that course. Flightlessness occurs quite commonly
and easily in avian lineages--as evidenced by the number of different times we
know it has occurred--and I presume that this tendency could have been even
stronger when birds were less modern and more dinosaur-like during the early
Mesozoic. The road from flightlessness to flying, however, seems far, far more
tortuous (in vertebrates, anyway); but I don't think it requires miracles.