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Re: new dinosaurs



On Fri, 18 Mar 2005 04:27:22 -0800 (PST), Tim Donovan <uwrk2@yahoo.com> wrote:
> 
> > Appalachiosaurus montgomeriensis (Carr, Williamson,
> > et Schwimmer 2005)
> 
>   It is considerably older than Dryptosaurus but the
> latter is said to be a relic of the Cenomanian, when
> Asian tyrannosauroid immigrants became isolated in
> eastern America.

Why Asian tyrannosauroids?
Let's review:

PRE-CAMPANIAN TYRANNOSAUROID CHRONOLOGY:
~195 Ma (Sinemurian/Pliensbachian, Early Jurassic)
----map of Earth: http://scotese.com/jurassic.htm
----(no tyrannosauroids known)
~165 Ma (Bathonian, Middle Jurassic)
----?_Iliosuchus incognitus_ (England, Europe)
~150 Ma (Kimmeridgian/Tithonian, Late Jurassic)
----map of Earth: http://scotese.com/late1.htm
----_Aviatyrannis jurassica_ (Portugal, Europe)
~145 Ma (late Tithonian, Late Jurassic)
----_Stokesosaurus clevelandi_ (Utah and South Dakota, North America)
~?130 Ma (Hauterivian, Early Cretaceous)
----_Dilong paradoxus_ (China, Asia)
~125 Ma (Barremian, Early Cretaceous)
----_Eotyrannus lengi_ (England, Europe)
~120 Ma (Barremian/Aptian, Early Cretaceous)
----?_Prodeinodon mongoliensis_ (Mongolia, Asia)
~95 Ma (Cenomanian, Early Cretaceous)
----map of Eath: http://scotese.com/cretaceo.htm
~?85 Ma (Santonian, Early Cretacoues)
----_Alectrosaurus olseni_ (China and Mongolia, Asia)
(corrections and additions welcome)

So the first trend I notice is--we don't really have much to go on
here: at most, seven species, each known from a few specimens at best,
a couple of bones or some teeth at worst. And the species are each
spaced out by about 5 to 35 million years.

But if you HAD to place a model on this, this one works best with the
(scant) data:
- origin in the early Middle Jurassic of Europe (connected to Asia and
North America at the time)
- dispersal into North America by the end of the Jurassic
- dispersal into Asia by the middle Early Cretaceous (from Europe or
from North America? or both? Who knows?)
- disappearance from Europe sometime after the middle Early Cretaceous
(displaced by abelisaurs from Africa? Who knows?)
- continued presence in Asia and North America throughout the Cretaceous
- disappearance at the end of the Cretaceous (of course)

Of course, it would only take a few discoveries to overturn this,
so--don't trust it.

> Are they certain it is a different genus?

It is now! ;)

--Mike Keesey