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Re: anti-social Tyrannosaurs

At 06:26 PM 12/10/98 -0600, Tim Bollier wrote:

Last things first:
>   Please feel free to correct my mistakes in concepts. But if you must play
>teacher and want to correct grammatical mistakes, spelling, or other
>"labels" that don't affect understanding the concepts, please reply off list
>so the others aren't indulged by things
>that don't further anyones interest in dinosaurs.

Gee, to whom could that be directed...?  :-)

Well, I don't "play teacher", I AM a teacher.  As such, I do like to keep
things accurate.  It was all in good fun, though, as Dwight Stewart himself
admitted.  Also, as it was such a common mistake, I felt it was important to
get it on the list, because he wasn't the only one who does it.

(Also, I don't tend to correct people's non-scientific grammatical mistakes,
except while editing or grading papers.  Heck, I make plenty myself.  But
taxonomy IS part of science, and does have a bearing here).

>   If we only believe in the facts we can touch, then Newton, Einstein,
>Darwin,Sagan, and Dr. King were only dreamers and not visionaries. We often
>need visions by great people so we will know what we are looking for as well
>as why.

Although the guys above are heros of mine, at least one (Sagan) would argue
on some of this idea of yours.  While beliefs are important, for they
certainly help guide us, it IS only the facts which drive Science.  For a
REALLY good discussion on this, see Sagan's book "The Demon-Haunted World:
Science as a Candle in the Dark".  I highly recommend it to everyone.

Along these lines, I may *believe* a lot of stuff about dinosaurs in
general, and tyrannosaurs in particular.  However, some of these are just
that: beliefs, dreams, and so on.  Because of this, I won't dwell on these
on the list:  get a few drinks in me, or get me out in the field, or get a
few drinks in me out in the field, and I'll spend hours talking about my
speculations on the life and times of the tyrant dinos.

Too many paleontologists (particularly ones who get in the mass media a lot)
do not distinguish between their personal beliefs about dinosaurs and their
world, and what can be demonstrated scientifically.  The lay public often
doesn't know how to distinguish the two, and take as gospel anything these
individuals say.

This is just as bad as the pre-Dinosaur Renaissance tacit acceptance of
dinosaurs as cold-blooded, stupid, malformed monsters.  We should always be
clear in distinguishing what we can demonstrate from the evidence, what we
can infer from comparative anatomy and behavior, and what is idle
speculation (appealing though it may be).  We should do this in general, and
we should do this here in particular, as this is not a "dinosaur chat line";
it is, as Mickey Rowe has to point out every so often, a list dedicated to
dinosaur *science*.

>   I believe tyrannosaurs may have lived in mixed social groups and that
>they probably exercised several social strategies during their long tenure
>on earth. The environmental pressures that drive both evolution and behavior
>would probably have shifted the best survival strategies  during the
>millions of years of their existence.

I would certain agree with these.

>   1. Large herds of herbivores probably gathered, if not year round, then
>for mating/birthing or migratory purposes. The herds would have devastated
>the local resources of plant life rapidly, even assuming the vegetation
>regenerated rapidly.

[snip discussion of migration and so forth]

Agreed.  If any herbivorous dinosaurs of the Late Cretaceous migrated,
hadrosaurids and ceratopsids certainly seem to be the main candidates, since
they a) were large bodied animals and b) at least some species within each
group are known to have gathered in vast numbers. 

>Given the  probable migration of these herds, then at least some of the
>predators probably also followed them. But which ones? The  tyrannosaurs
>were one of if not the top predator in the late cretaceous. Would that
>affect whether or not they migrated?

Here are some other reasons to suspect that, if any Late K North American
theropods migrated, it was probably tyrannosaurids:
a) tyrannosaurids are large bodied animals with long legs: they could cover
a lot more ground in a day than their contemporary smaller kin.
b) tyrannosaurids would be more likely to have been able to take down large
bodied prey (as in the theoretically migrating hadrosaurids and ceratopsids)
than their little cousins.

>Because I believed they scavenged first
>and hunted second (why risk injury needlessly)
>the lower food available might have forced some to follow the herds, but not

Although I don't object to this belief, it is good you stated it as such.
We really don't have a good idea of the relative frequency of predation vs.
scavenging in modern carnivores, much less extinct ones.  _Crocuta crocuta_
(the spotted hyena) was long thought to be primarily a scavenger, but the
field studies (including direct field observations) of Kruuk demonstrated
that some populations of hyenas get 70% of their food from predation, and in
Ngorongoro crater as much as 96%!

This shows the importance of doing science (observing, quantifying, etc.):
it may overturn long held, and even seemingly secure, beliefs.

>(I'm suspicious of dino live births).

As well you should be.  The recent Lee & Shine paper in the latest issue of
Evolution (mentioned by Ralph Chapman in one of his postings earlier this
week) has a brief discussion of some physiological reasons why archosaurs
may have been incapable of live births.

>So from my
>views, amateur be they may, this is how I see dimorphism and social
>strategies within tyrannosaurs.

An interesting scenario, and a detailed picture of the world of the

I don't have objections to scenarios and speculations: they are great.  The
certainly do have a place in science.

What I do have objection to, though, is when people treat scenarios and
speculations as superior to the evidence.  I object when people come up with
a speculation (appealing as it may be) and claim that it is the best belief,
or the only one that should be accepted.  You didn't do that, so I have no
problem with it.  I don't think anyone else here would.

Keep on dreaming.

Thomas R. Holtz, Jr.
Vertebrate Paleontologist     Webpage: http://www.geol.umd.edu
Dept. of Geology              Email:tholtz@geol.umd.edu
University of Maryland        Phone:301-405-4084
College Park, MD  20742       Fax:  301-314-9661