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Re: Copeing with mammals




On Sat, 27 Nov 2004, David Marjanovic wrote:

> ----- Original Message -----
> From: "John Bois" <jbois@umd5.umd.edu>
> Sent: Monday, November 22, 2004 5:22 PM
>
> > Pterosaurs clearly had issues.  As a clade, their extinction was long and
> > slow.  This argues against a long series of accidental extinction events.
> > It argues _for_ some kind of deficit relative to other clades.
>
> How? How does it?

Please.  _If_ it was long and slow, there are only two possible
hypotheses.  A gradual global replacement by better competitors, or an
incredible run of bad luck.  To argue the latter you have to say that if a
pterosaur died out there was always a neornithine competitor waiting in
the wings (as it were), _and_ that in every case, the neornithines waiting
in the wings were better competitors than the competing ptrerosaurs
waiting in the wings.  And this boils down to the same thing.  So, I'm
afraid you'll have to make your bed in a massive terminal extinction.

> > I have proposed a reasonable problem--that juveniles (or adults, for that
> > matter) were not as agile in the air as neornithines, and were therefore
> > more susceptible to predation/general harrassment.
>
> But you haven't provided any shred of evidence for this speculation.

Most agree that the two clades had significantly different flight
characteristics.  Of course I don't have evidence for the dominance of
one form in every niche.  But neither can you say that both were
equivalent and did not play out in competitive/predatory battles.  But
maybe  you are saying that.  If so, this is a funny kind of political
correctness: all species are equal.

> The keyword is "if". Not to mention the problems associated with evolving
> into an occupied niche.

But that is exactly what better competitors do! Unless you are hardline
Etheridgian (one who says that _all_ species distribution is a result of
past catastrophies and species taking advantage of open niches).

> > But what are you arguing?  That each pterosaur species extinction was
> > unrelated, caused by a separate environmental whim?
>
> I argue that this is possible -- although there's no evidence either way.

See above argument that this reduces to competive interaction anyway.

> However, never forget how poor the fossil record of pterosaurs in the LK is.
> We don't _know_ if _any_ pterosaur clade that is known from the EK went
> extinct before the K-Pg boundary. The most extreme examples are the
> anurognathids: although known from the MJ to the EK, they have to date
> _only_ been found in Konservatlagerstätten. Outside they seem to have left
> _no trace_ across some 60 million years!!! I don't know of a LK
> Konservatlagerstätte.

This is astonishing, indeed.  So, you suspect that pterosaurs were fully
diverse till the end?