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Re: Extinct vs Disappeared

 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