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Re: Everyone's discussing bird origins...



Rob Meyerson wrote: 

> In one of the populations, the trend for powered flight starts,
> leading to Archy.  At the same time, another population starts a
> trend which leads to Dienonychus.  Call this definition: Birds Are
> Dienonychus Cousins (BADC).

What you have chosen to call "BADC" appears to be the most favoured 
theory among palaeontologists, as far as I can ascertain.

> This senario overcomes one of my principal objections to BCF: what
> evolutionary trend would force a fully developed bird to adapt to a
> cursorial existance when the ground is full of small predators
> (read: competition).

Nevertheless, there's enough evidence from the Cretaceous to suggest 
that it DID happen, and quite a number of times in avian evolution.  
Apart from _Mononykus_ (which not everyone believes is a bird), 
there's incontrovertible Cretaceous avians such as _Patagopteryx_ 
(Argentina) and _Palaeocursornis_ (Romania) which were cursorial and 
terrestrial- living.

How they managed to come to earth in the first place and avoid ending 
up as lunch for a hungry dromaeosaur, I don't know.  I can only 
suggest that passed through a fully volant, cursorial stage on the 
way.  Once they became fully cursorial and were capable of 
outrunning predators, they could forsake their wings.

Aside from the aforementioned sprinters, there's also flightless 
aquatic birds like _Hesperornis_.  These also abandoned the powers of 
flight which Archie and friends went to so much trouble to evolve.

DISCLAIMER:  This posting is not to be interpreted as support, 
either explicitly or implicitly, for BCF!!!!!!!