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Declining pterosaur diversity




On Sat, 27 Nov 2004, David Marjanovic wrote:

> >> With that kind of fossil record next to nothing can be said about
(declining ptrerosaur diversity).
> >
> > Still, we manage quite well.
>
> Nobody but you has even tried for the last ten years or more.

Thank you...but let me decline the compliment.
Penny, D. and M.J. Phillips 2004 The Rise of birds and mammals: are
microevolutionary processes sufficient for macroevolution? _Trends in
Ecology and Evolution_ Vol.19 No.10 pp.518-522.

...in which is discussed five models for the biotic turnover at and/or
before the K/T boundary.  The authors propose inverting the traditional
question of "When did the last pterosaurs and dinosaurs become extinct?",
to "When did mammals and birds start replacing small dinosaurs and
pterosaurs?" (This is a question I have often asked on this list.)

Fueling this is an observed increase in diversity of birds and mammals.
They also supply some new data.  OK...the data suffer from the usual
problems (preservational bias, etc.) but they indicate a reduction in the
diversity of small dinosaurs from three time periods: E-M Cret.,
Campanian, Maastrichtian.

The authors offer this paper as a hypothesis for directing research.
Alternate hypotheses are valuable, etc., etc.

Lastly, the pushing back of placental evolution (you will recognize the
authors from previous papers re molecular estimates of divergence) insists
that these questions be asked.  The idea that often gets aired on this
list--that there is infinite ecospace, or rather, an infinite number of
niches created by division into smaller and smaller units when new species
come along--must be held to question.  So, to suggest some species become
extinct upon the arrival of new species--even without evidence of this
extinction--is not a radical claim.  And I am certainly not the only one
making it!

By the way, the placental/marsupial split is now at around 125 million
years ago according to SVP presentation by Luo,Z., Wible, and Yuan.