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RE: Tyrannosaur Evolution



Tim Donovan (uwrk2@yahoo.com) wrote:

<It's not even true. Western North America was then a relatively narrow
north south strip of land. The east was considerably larger, yet
Dryptosaurus was much smaller than T. rex.>

  There are a few reasons why the eastern fossils known were a tad smaller
than those in the west, due in part, it may be possible to asusme, the
nature of the fauna. 

  In the east, latest Cretaceous animals include *Nodosaurus textilis,*
*Dryptosaurus aquilunguis,* and *Hadrosaurus foulkii,* animals that are on
the whole smaller than those in the west by the order of about 30%. There
are a few substantive reasons why some animals don't get big, and one of
them is available resources (as noted, the size of the continent _should_
mean they had more room to roam, but we do not know the nature of the
eastern geography to determine the extent of upland/lowland/shore/montane
areas within which these animals would have been able to move in).
However, the predator/prey arms race certainly also has something to do
with things, and it is possible in the east things had not escalated to
the size and armament that they had in the west, nor does it seem a faunal
diversity had been reached that is comparable. (All based on erosional or
collection biases, of course.)

<Exactly. The West had titanosaur immigrants like Alamosaurus, which, as
Starkov proposed, caused the large T. rex to be selected for in inland
environments of the West.>

  Only in the south, and only with a select range of *Tyrannosaurus.* In
fact, some of the southern *T. rex* specimens have even been questioned on
their application to that species, much less that genus, given the maxilla
variation. This doesn't explain the collection of the consistently largest
animals in the north.

<But Labocania was only of Campanian age. So Bagarataan was a
tyrannosauriod, not a troodont?>

  Cranial anatomy indicates that the jaw derives from a tyrannosauroid.
Postcranial features would be plesiomorphic or convergent under this idea.
More than one phylogeny has come out with this, including Holtz (2004). I
am sure either Mickey will supply the detials, or already has....

  Cheers,

=====
Jaime A. Headden

  Little steps are often the hardest to take.  We are too used to making leaps 
in the face of adversity, that a simple skip is so hard to do.  We should all 
learn to walk soft, walk small, see the world around us rather than zoom by it.

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)


                
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