[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
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
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
Systematic ramblings: http://homepage.mac.com/john_conway/phylogenetic/