Re: Ah ha! That's where therizinosaurs came from

[Jason Brougham <jaseb@amnh.org>]

On Aug 8, 2011, at 11:22 PM, <GSP1954@aol.com> <GSP1954@aol.com> wrote:

> I have long been pointing out that all flightless "theropods" with 
> extensive flight adaptations are likely to be secondarily flightless because 
> no one 
> has come up with really satisfactory arguments for why and how those flight 
> characters evolved outside the context of flight, because early fliers 
> should have been spinning off neoflightless descendents that retain flight 
> characters, and the situation parallels that of ratites etc. 



There are reasonable arguments for why and how those characters evolved, and 
whether they are satisfactory or not is a matter of opinion. Moreover, 
argument, as a method in science, is probably best kept as only supplementary 
and subsequent to empirical analysis.

In one hypothesis, we actually see the characters in question in the process of 
being assembled on the lineage leading UP to flying birds, not DOWN from flying 
birds. That is a perfectly plausible hypothesis that, like the BCF one, can be 
tested and supported or falsified. 

If BCF is correct then we know nothing at  all about the ancestors of birds, we 
have no transitional fossils leading from primitive theropods to flying birds. 
That is perfectly plausible. But the maniraptorans that Paul considers 
secondarily flightless may instead reflect the transitional steps. Moreover, as 
Thulborn suggested, and Hopp and Orsen elaborated, many of these characters, 
such as long wing feathers and wrist folding mechanisms, may have evolved for 
perfectly reasonable uses before flight was in any way possible, and could have 
even functioned well in bigger land animals. Maybe the special pectoral anatomy 
of maniraptorans evolved to allow the parents to endure the strain and fatigue 
of shading their eggs with outstretched wings for fourteen or more hours at a 
sitting. I don't have to advocate that opinion, I need only repeat that it is a 
plausible hypothesis.