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Re: Dinosaur-relevant article for you statistics gurus




On Sat, 14 Aug 2004 08:45:24 -0400 "Andrew A. Farke"
<andyfarke@hotmail.com> writes:

> In their presentation of the data, I'm pretty horribly confused 
> (although if
> I go back to the Sheehan paper, which I don't have with me at home, 
> perhaps
> it would clear things up. For instance, their data table gives a 
> listing of
> "Number of dinosaur species per family in three Cretaceous periods." 
> The
> periods are divided into Upper, Middle, and Lower. For ceratopsians, 
> they
> list 50 species in the upper, 53 in the middle, and 19 in the lower! 
> I
> wonder if they are talking about specimens, instead. Anyone have the 
> Sheehan
> paper handy to confirm this?

Sheehan et. al (1991) don't talk about any other units (nor other times)
other than the Hell Creek Fm. (all of it uppermost Cretaceous). 
Furthermore, they (1991) counted "minimum number of individuals" (meaning
that if two bones are found in close proximimity and belong to the same
family, then the two bones were counted as one individual).  Sheehan et
al. only recognized elements down to Family level (although they provided
a table (Table 2) which lists the number of genera within each family in
the Formation.  In the case of Ceratopsidae, they list 2 genera for the
Hell Creek Formation).  Species are not dealt with.

They *do* break the Hell Creek Formation down into three stratigraphic
units (upper, middle, and lower).  Perhaps that is where the confusion
lays?

Reference:
Sheehan, P. M., (and four others). 1991.  Sudden extinction of the
dinosaurs: latest Cretaceous, Upper Great Plains, U. S. A.   Science
254:835-839.

<pb>
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