RE: Bakker's Brontosaurus and Late Cretaceous populations

["Thomas R. Holtz, Jr." <tholtz@geol.umd.edu>]

> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> Mike Lima
>
> Now a couple years
> later, I tried to find more on the subject but I'm
> still only finding similar vague statements. Has
> Bakker ever published or even stated on what grounds
> he distinguishes between the two?

The main reference for this would be Bakker's paper on Eobrontosaurus yahnipin 
(in the Lower and middle Cretaceous Ecosystems volume
of the New Mexico Mus. Nat. Hist. Sci. Bull. 14). Please note that Bakker is 
famous for a reputation of being an extreme taxonomic
splitter, so his "species and genus level differences" are often other people's 
"intraspecific variations." As even with modern
animals there are no guarenteed fool-proof method of determiing when two 
closely-related individuals are different at the species or
genus level, this is more matter-of-opinion than science.

> Also rather recently I found videotapes of a PBS four
> episode series simply called "The Dinosaurs" that my
> mom bought me when I was a kid and watched them again.
> In one of the episodes Bakker explains why he doesn't
> feel that a comet killed the dinosaurs, mentioning how
> frogs are very sensitive creatures and would have been
> the first to die, yet survived. One thing he said was
> that before their sudden disappearance from the fossil
> record the dinosaurs were already dying out. This
> blatantly contradicts what another paleontologist in a
> different episode of the same series says, claiming
> they were thriving. I could be mistaken, but in "When
> Dinosaurs Roamed America" I thought something was
> mentioned that in the time leading right up to their
> extinction that there was a relatively low number of
> species yet in an issue of National Geographic from
> 1999 on Sue, it explains that the dinosaurs were
> rapidly diversifying. How can their be such blatant
> contradictions on the matter?

To a large degree, it depends on what time scale and taxonomic level you are 
looking at. Most of the traditional work supporting "no
evidence for decline" has been looking at the species or family level within 
the Hell Creek or the Lance, and there is no sign of
decline that way.

Most of the traditional work supporting a decline looked at the subfamily level 
over the last 15-20 million years or so.

The recent work by Fastovsky (supporting a possible increase, or at least 
stable) looked at the species level over the whole of the
Cretaceous.

Too bad no one's looked at Campano-Maastrichtian dinosaurian diversity with an 
eye towards phylogeny... Oh, wait. Right.  See you at
Mesa, people! :-)

                Thomas R. Holtz, Jr.
                Vertebrate Paleontologist
Department of Geology           Director, Earth, Life & Time Program
University of Maryland          College Park Scholars
        Mailing Address:
                Building 237, Room 1117
                College Park, MD  20742

http://www.geol.umd.edu/~tholtz/
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