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Re: Utahraptor;Argentine carnosaur

>From: VanKathy@aol.com
 > Is the Argentine dinosaur a tyrannosaur? 

Probably not.  It is more likely to be an abelisaurid or something
similar to that.  Abelisaurids appear to be the dominant theropods
in South American during the Cretaceous.

That group is derived from the earlier ceratosaur lineage, and
is only distantly related to any of the large theropods elsewhere.
 > Sauropods existed to the end of the Cretaceous, and, in Titanosaurids,
 > possibly even became larger, yet sauropods are mostly discussed in a Jurassic
 > context.  Why don't we hear more about the later sauropods?  Were they simply
 > that much less common?

Yes.  For instance in the Maastrichtian of North America, only
one species of sauropod is know, Alamosaurus, and it is not found
in any of the major northern dinosaur sites.  And even where it
*is* found, it appears to be rather rare.

Nowhere in the Cretaceous is there the sort of sauropod diversity
that is found in the Morrison or Tendaguru formations of the
Late Jurassic.

 > Weren't they the only animals capable of fulfilling
 > their ecological niches?

Well, yes, but perhaps the niche became inappropriate due to
changing ecology.  During the Cretaceous there was a gradual
increase in the importance and diversity of flowering plants,
and a reduction in the extent of the open conifer woodlands that
seem to have dominated the Late Jurassic.
 > How can any sane, informed person, believe anything else but that the KT
 > extinction was caused by an impact with an extraterrestrial object?

Because there is some doubt that such an impact would be *sufficient*
by itself to do the job.

I certainly no longer doubt it was a *contributory* factor, but its
sole sufficiency is still in doubt.

In "Dinosaur Eggs and Babies" there is a note about the prevalence of
pathological eggs during the latest Maastrichtian in India, and a
mention of some evidence that the extinctions spanned a period of
around 300,000 years.  If this evidence stands up to closer scrutiny,
it would certainly indicate other factors were involved.  (However,
there are sampling issues that make such temporal resolution difficult
to attain in practice, and which can create a false impression of
a gradual process - so much more detailed study is needed).

There is also some equivocal evidence in the Hell Creek Formation
of North America that there was a period of reduced abundance of
dinosaurs for some undetermined time prior to the final extinction.
[Though the exact reason for the reduced fossil abundance in the
last few meters of the Hell Creek is still unclear].

swf@elsegundoca.attgis.com              sarima@netcom.com

The peace of God be with you.