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RE: Maastrichtian extinction





Tim Donovan wrote:

> > no less than four chasmosaurine species existing at the very
> > end of the Cretaceous: _Triceratops horridus_, _T. prorsus_,
> >_Diceratops hatcheri_ and _Torosaurus latus_.
>
>  True, but IIRC she indicated that only one-horridus-was common.

Common in the fossil record, that is.  Remember, you cannot judge the
abundance of species in a past habitat based on their relative abundance in
the fossil record.  There are preservational and ecological factors to
consider.  To put it simply, animals that hung around lakes and rivers were
more likely to end up at the bottom of said lakes and rivers, and therefore
more likely to be fossilized.

This may explain the rareness of Ankylosaurus in the Lance/Hell Creek, but not the others. Lambeosaurs and a variety of ceratopsids are abundantly preserved in older sediments.




>Do you have a better explanation for the mid Maastrichtian extinctions > and turnover?

As I understand, your explanation is that _Tyrannosaurus took over the
world.

I said the mid Maastrichtian extinctions and turnover, which affected only western North America and perhaps Asia.




I think if you want your hypothesis to be taken seriously, you have
to, at the very least, demonstrate what novel characters _Tyrannosaurus_
possessed that made it (in your words) an 'archpredator'.  What did
_RTyrannosaurus_ have that its predecessors (_Albertosaurus_ etc) didn't -
and which rendered lambeosaurs and centrosaurs utterly helpless, thereby
driving these taxa to extinction.


It is common knowledge that, in addition to greater overall size, Tyrannosaurus had more powerful jaws and more robust teeth than Albertosaurus. (Note that there is no evidence of attacks on Euoplocephalus by Albertosaurus but evidence of attacks on armored dinosaurs by Tyrannosaurus.) Also keener senses for finding prey (owing to very large olfactory lobes and the highest degree of forward or stereoscopic vision) and faster speed- conferred by longer legs- to catch it. IMHO, it isn't at all surprising that taxa which seem least able to resist attack or flee-the nearly hornless centrosaurines and relatively short legged, bulky lambeosaurs, respectively-were eclipsed by Tyrannosaurus. It reprsented a major leap in predatory capability, and not all of the contemporaries of Albertosaurus could adapt.



Tim W.


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