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Re: Large last gasp of pterosaurs



----- Original Message ----- 
From: "John Bois" <jbois@umd5.umd.edu>
Sent: Thursday, January 22, 2004 3:59 AM

> But pterosaurs as a clade seem to have had a long, gradual extinction.

http://www.cmnh.org/dinoarch/2003Jul/msg00405.html
Their fossil record is too bad to tell what their extinction looked like.
_All_ we can say for _certain_ is that so far we haven't found any in
Cenozoic strata yet, and that azhdarchids persisted at least until very
close to the boundary.

> Respectable scientists (Phil Currie,
> for e.g.) remark on a _lack_ of change in speciation across the boundary;
> and other respectable scientists w/out bones to pick (as it were) say the
> fossils indicate speciation not extinction (Archibald).  This is in answer
> to the claim that mammal demise contributed to the mass extinction body
> count.

Oh, this _still_ doesn't tell us how Djadochtatheria (Multituberculata) and
Asioryctitheria (Eutheria, e. g. Zalambdalestidae and Zhelestidae) died
out -- Zhelestidae seems to have occurred even in Madagascar (that's where
the "marsupial" tooth from there is now put). These groups are not known
from North America or any place with a good record of the late Maastrichtian
(and early Paleocene).

> And marsupials _may_ have been impacted by invasions and should
> not be included in the body count.

First I'd like to see a) good dates for the invasions and b) evidence that
the invaders _could_ have competed with the present fauna. To suggest that
*Protungulatum* competed with *Didelphodon* or *Pediomys* is like saying a
fox/duiker/pig/beastie is going to compete with Tassie devils or shrews. Yet
Stagodontidae (*Stagodon* is a junior synonym of *Didelphodon*) and
Pediomyidae are the 2 metatherian groups of North America that went extinct
at the boundary (the third, Peradectidae, to which *Alphadon* belongs,
survived until the late Miocene).

> How many organisms can you remove from
> the body count before organisms will cease being automatically lumped in
> there?

If metatheres are all you want to remove... those forams and haptophytes
were quite speciose... ammonites... plesiosaurs... mosasaurs...
non-neornithean dinos... that would still look suspiciously like a
catastrophic mass extinction.

> In other words there really may not be a
> connection between pterosaur extinction and the event at the K/T boundary.

Correct. But -- it's currently most parsimonious to suggest that there was
one. :-)