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Re: How Did Hadrosaurs Survive? (Was: Hadrosaur "mummy" questions)




From: "Rob Gay" <rob@dinodomain.com>
Reply-To: rob@dinodomain.com
To: "Dinosaur Mailing List" <dinosaur@usc.edu>
Subject: Re: How Did Hadrosaurs Survive? (Was: Hadrosaur "mummy" questions)
Date: Fri, 25 Oct 2002 08:31:17 -0700

>Hadrosaurs had keen senses which provided early warning of approaching
tyrannosaurs.<
Based on?

It is true that hadrosaur olfaction may be overrated, given new research by Evans which indicates rather small olfactory lobes. But IIRC, keen hadrosaur sight and hearing is indicated by schlerotic rings and stapes.


>It is also noteworthy that the longest or last surviving
 hadrosaurs, the edmontosaurs, had a relatively gracile build and the
longest legs to facilitate relatively fast escape.

But yet earlier Cretaceous hadrosaurs managed to survive long enough to
produce ancestor species, and become fossilize in relative abundance as
well, and they had to contend with "faster" tyrannosaurs.

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.



Look at HP Holtz's latest publication (available on PDF on his website), and
it talks about some paleobiological implications of large dinosaurian
predators (such as they would need a huge territory to prevent decimation of
the local fauna, may have preferred younger animals, etc.). Couple this with
the high reproductive rate of archosaurs in general,

Including tyrannosaurs.

and the fact that they
likely didn't need to eat every day (I can't think of any large bodied land
predator that eats every day, but I could be wrong), and some hadrosaurs
being gregarious, I don't really see a problem with hadrosaurs surviving.

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.


Warning! Speculative scenario below!!!:
If you figure a herd of 100 hadrosaurs (possibly a small number, based on
the Maiasaura bone bed, but let's keep it focused) in an area with 1
Tyrannosaurus, 2-3 ankylosaurs,

Ankylosaurus was not really part of the near coastal Lancian community. You must mean Edmontonia.



and a small herd (20) of Triceratops. Add in
herbivore migration. Assuming the Tyrannosaurus eats once a week (and may
not always be successful in bringing down prey), you may lose one or two
hadrosaurs before the herd exists its territory.

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.


Plus, there are other prey
items around, and we do know Tyrannosaurus snacked on Triceratops as well.

Maybe only scavenged on it.

Maybe its just me, but I don't see that big of a problem being able to
survive...I mean, we know they did manage to survive,

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.


I think understanding
exactly why we may require a greater understanding of the paleoecosystem,
for the hadrosaur fossils may not tell us what we need to know.
Done rambling.
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
Btw, Brett-Surman once told me
> that hadrosaurs were more manueverable than tyrannosaurs.
>
>
>
>
>
> So far as we
> >understand the morphology and its implications, the predators were
> >faster, stronger and probably smarter than their prey: so what _could_
> >a poor hadrosaur do once a tyrannosaur had decided to eat it?
> >
> >I tried to imagine an analogously unbalanced contemporary system, but
> >couldn't come up with one.  Looking at cheetahs and antelopes, which
> >was the closest I could come up with, you say that the predator is
> >faster, stronger and smarter than the prey, BUT because it's only
> >faster over short distances the antelope has great chance if it keeps
> >its eyes open -- which is why only a small proportion of attacks end
> >in kills.  But as I understand it, there's no reason to think a
> >hadrosaur could outdistance a tyrannosaur.
> >
> >So what am I missing?
> >
> >Is it just possible that the ecological setup could have been
> >something completely alien to what we see today?  How about this: when
> >a tyrannosaur wanted to eat a hadrosaur, it did; but they didn't eat
> >the babies,
>
> I don't know about babies but tyrannosaurs definitely ate subadlt
> hadrosaurs. Stomach contents indicate one may have been only several
months
> old IIRC.
>
>
> >
> >  _/|_ __________________________________________________________
>
>
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