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Re: How Did Hadrosaurs Survive?



Tim Donovan wrote:
>The most recent study, of Lance tracks, supports a fast Tyrannosaurus.<
Interesting. I was only aware of the single possible tyrannosaurid print
from NM being anywhere close to Tyrannosaurus in size. If you've got a
citation, I'd love to read up on it. Maybe I and others are wrong.

>No, they found more T.rex than Edmontosaurus, although new Triceratops
finds were three times more numerous.<
Source?


>They didn't have to hunt constantly to have an effect.<
What brings you to this conclusion?

>The Nemegtian environment was about as far inland as any, and certainly
suggests hadrosaur diversity waned far from the coast as well as near it.<
Forgive my lack of knowledge concerning Asian paleogeography, and
corresponding modern sediments, but what then is the nearshore Asian
deposit, to show that at the same time in the same area the fauna across the
board was changing.

>Essentially, only one hadrosaur genus is present, (only one lambeosaur
specimen was ever found)<
But none the less, it was still there then. It doesn't matter how many are
found, in precise terms, because the fossil record is incomplete. Unless
you're arguing that the single lambeosaur specimen was transported through
time from someplace else, then it indicates the presence of a population. It
had to have been born of two other animals of the same species, right? In
order for one to be present, you need to assume that there's at least a
large enough population to have a stable gene pool. Sure, they may not have
been a huge component of the fauna, but they were there, living alongside
those tyrannosaurs, and they still persisted.

>Btw, well inland Naashoibito and Javelina hadrosaur remains are considered
hadrosaurid, AFAIK.<
You missed the point...

>Eberth's abstract last year, for one thing.<
I don't have access to last years abstracts at the moment, so I will have to
with hold comments on this then for the moment.
I do remember, however, a poster last year at SVP that discussed how it was
unlikely that any large theropods were habitually hunting in packs.

>Didn't you read The Dinosauria?<
Yes. I've owned a copy since it came out in softcover. However, I have not
completely read through the hadrosaur section in a while, as my research
doesn't really (ever, so far) come into contact with hadrosaurs. I will then
here as well withhold my comments until I can reread the section on
hadrosaurs.

>The fact that all ceratopsids, some female, had horns suggests an
antipredator role was important.<
I strongly suggest you take a look at modern animals today, as well as work
done on sexual determination and sexual dimorphism in the fossil record.
Many modern animals have horns, regardless of sex. In the Thompson's
Gazelle, both males and females have horns, with the males possessing spiral
patterns, while the females tend to have unassuming straight horns. Water
Buffalo, IIRC, both sexes have horns. Some types of goats.
Several ceratopsid taxa show that their cranial ornamentation served no
defensive purpose whatsoever (I refer, of course, to Pachyrhinosaurus and
Achelosaurus, though Einiosaurus's horn may have also been pretty useless).

>Yes! T. rex was twice as massive, with a posteriorly expanded skull
providing much more area for muscle attachment.<
And, as others have pointed out, the prey was twice as massive. From a 25
foot long campanian hadrosaur to the 40-50 foot Anatotian, Shangtungosaurus,
etc., no wonder Tyrannosaurus was so big! If tyrannosaurs didn't increase
size right along side of the hadrosaurs, they would have gone extinct. Its
the basic "arms race" scenario, that's taught in intro biology courses.

>Ceratopsids and ankylosaurs obviously had to become larger, but why did
Edmontosaurus become so large?-it very likely didn't fight but fled. Unless
the longer legs of a larger hadrosaur made it faster, large size would have
been a disadvantage.<
Size IS defense. Look at African elephants. A pride of lions couldn't take
down a baby elephant, because it was simply too big, and too thick skinned.
Sharks don't hunt whales, eagles don't hunt bison, and its likely that
tyrannosaurus wouldn't want to tackle something much larger than them.

>Albertosaurus was not the immediate ancestor of T. rex. Its ancestor must
have evolved inland-as it is unknown in the Horseshoe Canyon. <
We'll never find the immediate ancestor, but I think its safe to assume that
it evolved alongside hadrosaurs, right? As you have stated, they were all
over the place. So why wouldn't the hadrosaurs adapt alongside, instead of
dumbly getting picked off one by one as T. rex evolved.

Bill Hunt wrote:
>Lions spend 90% of their time sleeping and lazing around.  One wildebeast
will keep the pride fat and happy for about 3 days, depending on the size of
the wildebeast and the size of the pride.<
Exactly the point I was trying to make, but I didn't have the statistics at
hand. Thanks.

>Ever been kicked in the head by a Zebra?<
Exactly! Even though something may seem defenseless (like a hadrosaur, or a
zebra) at first glance, it will have a way of defending itself and avoiding
predation. Animals don't tend to evolve towards more easily edible.

>Weren't Hadrosaurs and Ceratopsains the most abundant herbivores of the
late Cretaceous, and T-rex relatively rare?  Just like modern predator/prey
ratios?  The dinosaurs may be gone but the fundamental
principles of ecology still apply<
Precisely. I think that a lack of understand of the way ecosystems evolve
and operate has played into the development of this argument.
Done for the moment, until my eye catches some new e-mail begging to be
replied to ;)...or until I read that hadrosaur chapter again, whichever
comes first.
Peace,
Rob

Student of Geology
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Northern Arizona University
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