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Re: Extinct vs Disappeared

the most appropriate ref for mammal extinctions up to and including the K-T in 
the Hell Creek area is:

Journal of Mammalian Evolution, Vol. 12, Nos. 1/2, June 2005
Mammalian Faunal Dynamics During the Last 1.8 Million Years of the Cretaceous 
in Garfield County, Montana
Gregory P. Wilson
Abstract: This study provides an analysis of biotic change in successive 
mammalian communities during
the last 1.8 million years of the Cretaceous (67.3â65.58 Ma) from the Hell 
Creek Formation
in Garfield County, Montana. Results show changes in relative abundances of 
species, mean
individual body size, and to some extent taxonomic composition through the Hell 
Creek Formation.
These results are interpreted as ânormalâ mammalian responses to fluctuating 
temperatures during
the latest Cretaceous. By contrast, the extinction of 22â27 mammalian species 
at or near the
Cretaceous-Tertiary (K-T) boundary cannot be explained by the coincident 
cooling interval alone.
At the scale of temporal resolution available, these fossil data are 
inconsistent with an extended
gradual pattern of extinction (linear-response) and are most consistent with 
either a non-linear
response pattern for the K-T extinction, resulting from the accumulated stress 
of multiple longand
short-term environmental perturbations (e.g., climate change, sea-level 
regression, volcanism,
an extraterrestrial impact), or a single, short-term cause (an extraterrestrial 

Denver Fowler

----- Original Message ----
From: Phillip Bigelow <bigelowp@juno.com>
To: dinosaur@usc.edu
Sent: Sat, 6 March, 2010 17:10:06
Subject: Re: Extinct vs Disappeared

You're right.  I mis-wrote.
I meant to write that in OTHER K-T boundary zones in Fort Peck area, which were 
non-channeled, Archibald tended to favor the hypothesis of gradual replacement 
of Cretaceous mammals with Paleocene "aspect" mammals.  For what its worth, I 
believe he has since come over to the Sid
Archibald never studied the Bug Creek beds in any great detail.


---------- Original Message ----------
From: Denver Fowler <df9465@yahoo.co.uk>
To: dinosaur@usc.edu
Subject: Re: Extinct vs Disappeared
Date: Fri, 5 Mar 2010 23:29:55 +0000 (GMT)

Phillip Bigelow wrote:

>Back in the 1980s, J.D. Archibald suggested that the Bug Creek Beds that 
>"straddle" the K-T Boundary in Montana (actually, they don't straddle it at 
>all, but I digress) represent a gradual replacement of "Cretaceous-aspect" 
>mammals with "Paleocene-aspect" mammals.
>Archibald's hypothesis is extremely hard to prove for a variety of reasons, 
>but mainly because the Bug Creek Beds are so localized that they only 
>represent a small geographic area (1 mi^2 is all there is of them).
>You have to use Occam's Razor in situations like this.  If you look at the Bug 
>Creek Beds, their bottoms are channeled deeply into Cretaceous rocks. The 
>stratigraphic relationships between the beds and the Paleocene Tullock 
>formation is less clear, but the proximity of the beds to the K-T time horizon 
>should be taken into account.
>The most likely scenario is that the Bug Creek Beds represent mixing of animal 
>skeletons from different time periods (K and Paleocene).

The "bug creek problem" was solved by Lofgren (1985), who showed it was 
Paleocene channels incising into the Hell Creek Fm, reworking and mixing the 

Lofgren, Donald L. The Bug Creek Problem and the 
Cretaceous-Tertiary Transition at McGuire Creek, Montana. Berkeley:  University 
of California Press,  1995. 


Denver Fowler


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