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Re: How Did Hadrosaurs Survive?




From: "Rob Gay" <rob@dinodomain.com>
Reply-To: rob@dinodomain.com
To: <dinosaur@usc.edu>
Subject: Re: How Did Hadrosaurs Survive? (Was: Hadrosaur "mummy" questions)
Date: Fri, 25 Oct 2002 15:23:59 -0700

>This is not at all certain. T. rex had the longest legs of any tyrannosaur,
and probably the keenest senses. Its advent could have spelled an end to
certain taxa, including some hadrosaurs, which managed to survive the
smaller and less capable Albertosaurus.<
I refer you to the Hutchinson and Garcia paper, with the data plot of
probably speed ranges (if I'm remembering the paper correctly, of course) in
some dinosaurs, Albertosaurus included. It plotted as likely being able to
move faster than Tyrannosaurus. Anyways, if you're the biggest animal of
your type, of course you'll have longer legs than your smaller cousins. That
won't make you fast though. Its like saying that since Argentinosaurus had
longer legs than Apatosaurus, it would obviously be faster. There's other
factors that come into play here.

Giant sauropods weren't built for speed, tyrannosaurs were. Bakker just wrote there's no evidence larger theropods were slower; longer legs probably conferred faster speed.


> Including tyrannosaurs.<
Yes, including tyrannosaurs. But 1 tyrannosaur laying 9 eggs still won't
outdistance 100 hadrosaurs, 50% of them laying 12-16 eggs each. Factor in
infant mortality...

That ratio doesn't seem credible. More T. rex specimens were found recently in the Hell Creek than edmontosaurs; Triceratops is most abundant.




>Hadrosaur diversity apparently waned with the advent of T. rex. It is noteworthy that the relatively bulky, short legged lambeosaurs didn't fare as well as the more gracile, longer legged edmontosaurs.< Based on Hell Creek, right? Seems like a pretty localized example, that may or may not represent real local trends, let alone regional trends.

Same for Scollard, Lance, Frenchman, Ferris, probably the Naashoibito. Hadrosaurines are virtually the only remaining NA hadrosaurs of the late Maastrichtian.




>Ankylosaurus was not really part of the near coastal Lancian community. You
must mean Edmontonia.<
I didn't specify a genus, actually. I said ankylosaurs, not Ankylosaurus, so
I think Edmontonia would work...unless I'm wrong about what an ankylosaur
is.


>    Didn't you mean exits? They would then suffer losses in another T.
rex's territory. If lambeosaurs are attacked or caught more often,
edmontosaurs would fairly quickly predominate<
Yes, I did mean exits, I'm sorry that in my rush to get off to class I
misspelled a word. None the less, yes, they would suffer losses in another
territory, provided a)they were moving into a territory that didn't have
another herd there b)the Tyrannosaurus in question hadn't already fed, and
wanted to eat right away. You can't assume that as soon as a herd of
hadrosaurs walks into some animal's territory, that the Tyrannosaurus in
question goes out right away, and terrorizes the new herd until it leaves.

It's probable, given elevated metabolic rates and correspondingly great food demands.



>Maybe only scavenged on it.<
I thought we had healed bite wound on a Triceratops specimen, but I may very
well be mistaken.

There is healed damage to an Edmontosaur tail; I don't know if T. rex bite marks on Triceratops bone are healed.



>Apparently not all of them alongside T.rex. Bttw, the recently described Hell Creek lambeosaurine was found stratigraphically low, and may have disappeared early in the Lancian period; it is certainly far rarer than Edmontosaurus and Anatotitan.< Or lambeosaurs were living in environments not preserved in the record,

Where? AFAIK, all identifiable hadrosaur remains in far inland environments of Lancian age e.g. Naashoibito, are hadrosaurine.


or
this particular genus went extinct due to competition with other hadrosaurs.

Sure, it was less able to evade T. rex. If hadrosaurines were better able to compete for food, why didn't the lambeosaurs disappear much earlier? Why were they still abundant in the late Edmontonian period, just prior to T. rex?



Seems hard to pin the extinction of a clade on an animal not seen
contemporaneously with the animal in question before its extinction.

But lambeosaurs were contemporaneous with T. rex at the outset of the Lancian, and T. bataar, just prior to that.




>I almost forgot: Rob's scenario, with only 1 Trannosaurus occupying a
territory, flies in the face of evidence suggesting gregarious behavior.
IIRC three Tyrannosaurus bonebeds are known with individuals of various
ages.<
Once again I refer you to the Holtz paper, which does not say that
gregarious behavior wasn't possible, but it does note that for a large
carnivore to be able to feed itself based on the known ecological
constraints of the environment, the area for one would be _huge_! Its likely
that the larger a predator is, the more likely it is to remain solitary,
because it will then need to defend more space. Lions are the only animal I
can think of that doesn't go along with this. The other big cats are
solitary, but smaller animals, such as wolves, coyotes, hyenas are all
gregarious.
Besides, I don't know of any Tyrannosaurus bone beds, and the only
tyrannosaur bonebed I can think of would be the Barnum Brown/Currie
Albertosaurus bonebed.

But there are about 3 sites which have yielded T. rex specimens found in association with others of their kind. It probably was a pack hunter.



Hopefully I've caught all my spelling errors this time.
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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