Re: birds vs. pterosaurs

[John Conway <john_conway@mac.com>]

On Wednesday, July 24, 2002, at 01:04  PM, GSP1954@aol.com wrote:

> I address various aspects of birds versus pterosaur evolution over time 
> and
> maximum size in Dinos Air for those who are interested.

In DA Greg Paul writes:

> One possibility is that is that small pterosaurs declined on their own, 
> and birds merely took advantage of the situation by filling the vacant 
> niches as they became specialized aerial giants. We can "test" this 
> view via a thought experiment. Assume that birds never evolved and 
> therefore the Mesozoic skies were the domain of insects and pterosaurs. 
> If ther were no birds, would pterosaurs have abandoned the small size 
> of the size spectrum, if at all? After all, they had been doing well as 
> small fliers for over 100 Myr. The Evolution of giant pterosaurs should 
> not have influenced the evolution of small examples any more than the 
> evolution of avian giants has hindered the evolution of small birds. 
> So, while it is possible that small pterosaurs would have disappeared 
> without the influence of avian competitors, the proposition can be 
> considered dubious, if not implausible.

I have argued before that "competition" may by the wrong term to use if 
we are talking about replacement via speciation into vacant niches. So 
while I agree that small pterosaurs would have continued if birds had 
not evolved, I have argued that birds did not "out-compete" them.

It seems to me that there are two very distinct processes here: 
ecological competition, and speciation into vacant niches. I suppose the 
latter could be argued to be a sort of "competition", the competition of 
speciation rates. If there are proper terms for these two alternatives, 
I would like to know them.

To me, the very slow nature of the pterosaur-to-bird shift suggests that 
ecological competition at the species level was not the prime cause of 
the small pterosaur decline, because even a very small advantage for one 
species causes the very rapid exclusion of its competitor.


John Conway, Palaeoartist

"All art is quite useless." - Oscar Wilde

Protosite: http://homepage.mac.com/john_conway/
Systematic ramblings: http://homepage.mac.com/john_conway/phylogenetic/