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Re: birds vs. pterosaurs

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/