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Re: Hadrosaurs etc




From: GUY LEAHY <xrciseguy@prodigy.net>
To: rob@dinodomain.com, Dinosaur Mailing List <dinosaur@usc.edu>
CC: jonathan.r.wagner@mail.utexas.edu, msdonovan66@hotmail.com
Subject: Re: Hadrosaurs etc
Date: Sat, 2 Nov 2002 14:23:01 -0800 (PST)


The complete reference for Gregory Erickson's chapter is below:
Erickson G.M. (2000.) Breathing life into Tyrannosaurus Rex. pp. 267-275 in The Scientific American Book of Dinosaurs, Gregory S. Paul (Ed.) St. Martin's Press, New York.
Here's the relevant passage from the chapter:
"She (Aase Roland Jacobsen of the Royal Tyrrell Museum) surveyed thousands of dinosaur bones from Alberta, and learned that unarmored hadrosaurs were twice as likely to bear tyrannosaur bite marks as are the more dangerous horned ceratopsians. (Darren) Tanke, who participated in the collection of these bones, relates that no bite marks have been found on the heavily armored, tanklike ankylosaurs."

This is not surprising; given its persistance to c mid Maastrichtian Euoplocephalus was undoubtedly well protected from Albertosaurus. But T. bataar/rex evolved more robust teeth, and there is evidence for attacks on contemporary armored dinosaurs e.g. a Lancian Edmontonia and PIN 3142/250.




Concerning the biostratigraphic arguments, the only way to demonstrate the relative ages of terrestrial units, such as the Nemegt, is using radiometric dates and magnetic stratigraphy.

No. Shuvalov dated the Nemegt as Maastrichtian based on Mesolanistes etc.


Using populations of large, rare animals (i.e. dinosaurs) to precisely date formations, particularly from wide geographic locations, is simply too unstable on anything but the most general timescales. There is no way at this point to know if Tyrannosaurus/Tarbosaurus first evolved in Asia and migrated to NA, or vice versa.


Daspletosaurus is known only from North America, where tyrannosaurs existed continuously in the Campano-Maastrichtian period. In contrast, the Asian tyrannosaur record between the Baynshirenian and Nemegtian periods is poor or nonexistent, even in Barungoyotian fluvial beds that have yielded large prey taxa. In light of that, and the co occurrence of T. bataar with at least one American immigrant, Saurolophus (which was numerous and presumably coadapted) an American origin for Tyrannosaurus, albeit in an undocumented inland environment, seems most likely.



There is also no way at this time to confidently determine whether populations of Saurolophus in the Nemegt or Horseshoe Canyon Fms are the same age, or whether one is younger or older than the other.

Edmontosaurus lived from the Campanian to the end of the Mastrichtian, but Saurolophus is only known from c mid Maastrichtian in NA. The presence of a close relative of T. rex in the Nemegt, albeit smaller and less derived, is also consistent with this age.



Rob Gay <rob@dinodomain.com> wrote:>Troodont teeth are still more numerous there, aren't they?<
I didn't find any, but that doesn't mean that no one else found one. I do
remember walking by another tyrannosaurid tooth, and thinking it was a leaf.
My friend did the same thing. Then the lady behind her said, "Hey! Look at
that tooth!" We felt like dopes. Not really relevant, but I think its funny.


>Right, but Lancian hadrosaurs didn't fit that description, nor mid
Maastrichtian ones.<
They did to _their_ predators.

>Sometimes locating an abstract is like finding a needle in a haystack but
IIRC the author was T. Ford.<
Originally titanosaur armour (IIRC) was thought to be ankylosaur armour,
until someone demonstrated otherwise. Could this be the reverse of this? If
not, and if HP Ford is really the author (and its been fully published, of
course), perhaps he could comment.

>Some of the well inland environments e.g. Javelina, were clearly titanosaur
dominated. Some hadrosaurs were present but not necessarily the same types
as in the lowlands.<
So they would be lambeosaurs then, if they weren't the lowland forms (as
you've been saying lowland=hadrosaurid, uplands=lambeosaurs). In the North
Horn, we had primarily titanosaurs and ceratopsians, but hadrosaurs were
present for sure, and we had a TON of eggshell that closely matched what is
known about hadrosaur eggshell (IIRC), along with theropod eggshell.


>Perhaps both of you are.<
Perhaps you should e-mail Dr. Erickson with your ankylosaur data. Maybe he
can comment better.

>Hadrosaurs obviously faced a new predator; why are famine and disease as
testable?<
Because the point I was making is that your hypothesis ISN'T testable. We
can't test Tyrannosaurus sweeping like a Mongolian horde into the lowlands,
we can't test is preferentially eating lambeosaurs, we can't test most/all
of your statements/hypothesis, as others such as HPHoltz and HP Williams
have pointed out (or at least tried to). Science isn't about dogmatic
beliefs, science is about testable hypothesis, and your statements to this
point have been mostly counter to that. I asked the question: "What evidence
would you need to disprove your ideas?" Every paleontologist should be able
to ask themselves this, because its _testing_ their hypothesis. If you're
unable to do this, I think it falls into (entrenched, in this case) opinion,
and not science, and therefore does not belong on this list. I motion this
thread be closed.
Peace,
Rob


Student of Geology
400 E. McConnell Drive #11
Northern Arizona University
Flagstaff, Az. 86001
http://dinodomain.com
http://www.cafepress.com/robsdinos
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