[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
Re: How Did Hadrosaurs Survive?
From: "Rob Gay" <email@example.com>
To: "Dinosaur Mailing List" <firstname.lastname@example.org>
Subject: Re: How Did Hadrosaurs Survive?
Date: Mon, 28 Oct 2002 16:07:51 -0700
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.
See current abstracts volme.
>No, they found more T.rex than Edmontosaurus, although new Triceratops
finds were three times more numerous.<
All I remember is the news being posted in some online list.
>They didn't have to hunt constantly to have an effect.<
What brings you to this conclusion?
Even if a tyrannosaur pack killed only 2 hadrosaurs a week, or 100 a year,
it could cause one species to gradually replace another if a slower species
made up the bulk of the kills.
>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
board was changing.
The Wangshi and later Tsagayan environments had diverse hadrosaurs but
wre supplanted by a Nemegtian fauna with essentially just Saurolophus. The
Dinosauria indicates that "Albertosaurus" periculosus and Saurolophus
kryschtofovici are not from the Tsagayan but from an unnamed unit,
considered of Nemegtian age by Lucas.
>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.
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.
But apparently not for long since, in addition to being extremely rare,
both the Nemegtian and Hell Creek lambeosaurs occur stratigraphically low in
their units. They were apparently dying out.
>Eberth's abstract last year, for one thing.<
I don't have access to last years abstracts at the moment, so I will have
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
here as well withhold my comments until I can reread the section on
>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
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).
Exactly! And notice that these centrosaurines failed to survive alongside
T. rex, while the better armed chasmosaurines did-although even they had to
>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.
Yes, but only after Tyrannosaurus appeared. Euoplocephalus stayed the
same size alongside Albertosaurus all the way to the midpoint of
From a 25
foot long campanian hadrosaur to the 40-50 foot Anatotian,
Shantungosaurus was from the Wangshi series
of Campanian age and was not a contemporary of T. bataar or rex.
etc., no wonder Tyrannosaurus was so big! If tyrannosaurs didn't increase
size right along side of the hadrosaurs, they would have gone extinct.
It worked the other way around. Some giant hadrosaurs and big ceratopsids
e.g. Pentaceratops, already existed in the Campanian, but did not stimulate
the evolution of very big tyrannosaurs-although Alamosaurus might have.
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.
But Tyrannosaurus was far larger in relation to virtually all of its
contemporaries. Edmontosaurus was only of comparable size, and lacked
obvious weapons to fight off attack.
>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
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.
Of course some hadrosaurs adapted. Edmontosaurus was relatively gracile
and long legged-exactly the assets needed to escape.
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
the wildebeast and the size of the pride.<
Exactly the point I was trying to make, but I didn't have the statistics at
>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
Student of Geology
400 E. McConnell Drive #11
Northern Arizona University
Flagstaff, Az. 86001
Unlimited Internet access for only $21.95/month. Try MSN!