Re: Improper question re. extinction

[Peter Sheehan <sheehan@csd4.csd.uwm.edu>]

On Fri, 13 Jan 1995, Tom Holtz wrote:

> >
> >My apologies to everyone...I did, infact, want to deal at a much
> >broader level than species.  Families, would probably have been a much
> >better choice.
> >
> >When discussing the "bang or whimper" question of extiction, I wanted
> >to point out to them that dinosaurs were becoming less abundant and
> >less diverse by the end of the Cretaceous, and merely wanted to flesh
> >out the remarks with some specific information.
> 
> Actually, since you were interested in showning the decrease in diversity,
> then "Family" is an inappropriate rank to show.  All the common families of
> dinosaurs that were around in the late Campanian made it to the end of the
> Cretaceous.
> 
> The decrease in diversity occured below the level of traditional "families".
> 
> To put it another way: the family Elephantidae is still doing fine at the
> family level, but such a statement doesn't reflect the fact that half a
> dozen species or more of elephantids have died off in the last half million
> years (and the remaining two aren't in too good a shape, either).
> 
>                               
> Thomas R. Holtz, Jr.                                 
> tholtz@geochange.er.usgs.gov


But the dinosaur record is not like the elephant record.  Dinosaur 
abundance at any time in the Mesozoic reflects the quality of the record 
at that time, not the original abundance of dinosaurs.  

People suggesting that there was a decrease in abundance are simply not 
recognizing the poor record that exists.  How many intervals (e.g. early 
Maast.) have good collections from more than 4 or 5 local areas around 
the world.  Late Maast. for example has most of the known global 
diversity comming out of a single formation--the Hell Creek.  

How can we talk about global diversity patterns when most of the record 
comes from a single formation?  The record of dinosaurs is inadequate to 
examine global diversity.

We need to look for changes in local communities through time in areas 
where the communities can be traced through an interval of time.

Peter Sheehan