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Re: [dinosaur] When did T. rex evolve?



It is quite possible that the specific species Tyrannosaurus REX did not appear until pretty late. The holotype in Pittsburgh is very high up in the Hell Creek near the K/Pg boundary, along with Triceratops prorsus. The Tyrannosaurus in the lower Hell Creek and Lance which were laid down over ~1.5 million years differ from those high up and may be different species, much as appears to be true of Triceratops with T. horridus being low down. As for when and where Tyrannosaurus the genus showed up who knows, the earlier Maastrichtian time appropriate sediments probably don't exist. And don't believe all those citations of Tyrannosaurus existing in scattered formations hither and yon out west in the earlier Maastrichtian, it's too fragmentary to assess. 

Most Tyrannosaurus skulls and skeletons can be approximately placed stratigraphically. Ironically the worst data is for the good old 5027 in New York. That's because its quarry has been flooded by the damn Fort Peck dam. And whose to blame for that? Why that New Dealer Franklin Delano Roosevelt. 

GSPaul


-----Original Message-----
From: Thomas Richard Holtz <tholtz@umd.edu>
To: Poekilopleuron <dinosaurtom2015@seznam.cz>
Cc: DML <dinosaur-l@usc.edu>
Sent: Mon, Sep 18, 2017 6:23 am
Subject: Re: [dinosaur] When did T. rex evolve?

It is not certain. For one thing, the age of the lower boundary of the Hell Creek is not as securely dated as the upper. Secondly, the stratigraphic level of many of the classic specimens are not firmly placed in the context of Hell Creek stratigraphy.

That said, it is probably not older than 67.4

On Mon, Sep 18, 2017 at 4:38 AM, Poekilopleuron <dinosaurtom2015@seznam.cz> wrote:
Good day,

I would like to ask, what is the most exact geologic age setting for _Tyrannosaurus rex_? Lower limit would be 66.0 mya of course, but what about its earliest fossil remains? One study gave age of some 67.4 mya, but is that generally agreed upon? Thank you in advance, Tom



--
Thomas R. Holtz, Jr.
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