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Re: Hadrosaurs etc


From: "Rob Gay" <rob@dinodomain.com>
Reply-To: rob@dinodomain.com
To: "Dinosaur Mailing List" <dinosaur@usc.edu>
Subject: "Will the (hadrosaur) circle be unbroken?"
Date: Fri, 1 Nov 2002 15:15:18 -0700

>I didn't say that. A T. rex bite should be just as deadly on a hadrosaur.<
I remember a statement to the effect of Tyrannosaurus not wanting to prey on
ceratopsians because of their horns, and a refutation of unhealed bite
wounds on a Triceratops specimen showing that they were not preyed upon.

AFAIK, it is not known if those bite marks represent active predation or scavenging. T. rex may have preyed on Triceratops but there's no proof, whereas hadrosaur stomach contents have been found in a tyrannosaur.



>I didn't say that; there is proof that tyrannosaurs ate juvenile hadrosaurs
but not hatchlings.<
Not sure what the proof is, 

  There was an abstract about it a while ago.

but I would agree that they'd go after juveniles
over infants.

Great. 

>I pointed to the absence of tyrannosaur teeth at hadrosaur nests as
evidence that tyrannosaurs didn't attack the nests or adult hadrosaurs
didn't fight back.<
At Egg Mountain in '98, I found an tyrannosaur tooth about 20cm away from a
nest site.

Troodont teeth are still more numerous there, aren't they? 

>Some NA titanosaur armor has been reported;<
Reference please?

Sometimes locating an abstract is like finding a needle in a haystack but IIRC the author was T. Ford.

>in any case Alamosaurus was far more massive than Tyrannosaurus and may not
have needed it-although
the ability to survive is not the same as invulnerability<
Of course; nothing is ever truly "invulnerable". But you can get pretty
close to it by being too big to be preferentially preyed upon.

Right, but Lancian hadrosaurs didn't fit that description, nor mid Maastrichtian ones.

>Do zebra and wildebeest herds regularly fight lions or flee, fighting as a
last resort?<
But they do fight, and fight pretty well, regardless of time during the
hunt. Hence the "equation" I had in the previous post Size+Herding=Good
Defense. I mention neither flight or fight in this equation.

>But T. rex initially represented a new and more effective predator, and
several Edmontonian herbivores evidently could not survive alongside it<
Maybe this is my biggest issue here: if Tyrannosaurus evolved in isolation,
or was introduced into NA from someplace else, I can see a population being
negatively effected. But, I see no evidence from my knowledge of
paleogeography, of any isolated areas where T. rex could evolve, without
hadrosaurs, and then "reinvade" the rest of North America/the northern
hemisphere.

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. There was no close relative of Tyrannosaurus alongside Hypacrosaurus in the late Edmontonian. It and other taxa could have been "taken by surprise" when Tyrannosaurus arose and spread. 

>Including lions.<
Yes, including lions, although they have litters between 2-6, whereas Zebra
and wildebeest have usually 1 offspring per cow.

At least those offspring have a better chance of survival than hadrosaur hatchlings; like crocodilian hatchlings they must have been heavily preyed upon.

>Or Edmontosaurus and lambeosaurs. There is a nice illustration on page 338
of THE COMPLETE DINOSAUR.<
I was trying to compare generally contemporaneous animals, but none the less
I'd be interested to see this illustration. I don't have access to this
book. Can someone send a scan?

>I'll say.<
But you don't provide a reference, only derisive comments. I'll refer you to
HP Leahy's post, which I quote below here:
"In Gregory Erickson's chapter in The Scientific American Book of Dinosaurs,
he notes that bite marks are significantly more common on hadrosaurs than
ceratopsians, and that ankylosaur remains show no evidence of bite marks."
So perhaps I'm not as ill-informed as you may think.

Perhaps both of you are. A nodosaur from Grease Creek displayed pitted and chipped dorsal armor; predation was one suggested cause. And there is the puncture wound on PIN 3142/250. 

>What other factor(s)? Didn't I already address your suggestion that
hadrosaurine competition was responsible?<
You dismissed it, citing that they had different feeding heights (which I'm
not sure there's much evidence for)

I also mentioned that lambeosaurs lasted alongside other hadrosaurs for several million years and were still numerous c mid Maastrichtian.

. Factors could include famine, disease, 
competition for food/space/water, decreasing gene pool, hyperspecialization
(which leads animals to be less able to adapt), among others. All of which
are about as testable as your hypothesis.

Hadrosaurs obviously faced a new predator; why are famine and disease as testable? 


Peace,
Rob

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


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