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Re: How Did Hadrosaurs Survive?

From: "Rob Gay" <rob@dinodomain.com>
Reply-To: rob@dinodomain.com
To: "Dinosaur Mailing List" <dinosaur@usc.edu>
Subject: Re: How Did Hadrosaurs Survive? Date: Mon, 28 Oct 2002 10:29:09 -0700

>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.<
But did he do biomechanical analysis. Once again, I suggest you check out
the paper.

The most recent study, of Lance tracks, supports a fast Tyrannosaurus.

>That ratio doesn't seem credible. More T. rex specimens were found recently
in the Hell Creek than edmontosaurs; Triceratops is most abundant.<
Because people are more interested bringing home a Tyrannosaurus over
another Edmontosaurus.

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

>Same for Scollard, Lance, Frenchman, Ferris, probably the Naashoibito. Hadrosaurines are virtually the only remaining NA hadrosaurs of the late Maastrichtian.< Isn't Charonosaurus Maastrichtian?

Sure, but there is scant evidence for Asian tyrannosaurs in the Barungoyotian period, even in fluvial beds that have yielded hadrosaurs and sauropods. Maybe the primitive Asian hadrosaurs persisted longer in the absence of an effective culling agency in Asia prior to the Nemegtian. Btw, the putative late Maastrichtian age of the Tsagayan was rejected by Wagner onlist last year.

>It's probable, given elevated metabolic rates and correspondingly great
food demands.<
And the great amount of food provided by one hadrosaur kill. Modern
predators don't hunt all the time, it is unlikely that dinosaurs did either.

They didn't have to hunt constantly to have an effect.

>Where? AFAIK, all identifiable hadrosaur remains in far inland environments of Lancian age e.g. Naashoibito, are hadrosaurine< Farther away from the coast. Deep within forests not on floodplains. Dry-weather environments. Mountains. Lots of places don't get preserved in the fossil record.

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. Essentially, only one hadrosaur genus is present, (only one lambeosaur specimen was ever found) whereas the Tsagayan had several. Btw, well inland Naashoibito and Javelina hadrosaur remains are considered hadrosaurid, AFAIK.

>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?< Because replacement doesn't happen overnight.

But the hadrosaurines had existed alongside the lambeosaurs for millions of years prior to the late Edmontonian, yet the latter still seem dominant or numerous. Furthermore, lambeosaurs may have been higher feeders, given their higher neural spines-which Bakker equated with rearing ability- it's not at all clear there was competition for food.

>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.< A reference would be useful, if you could.

Eberth's abstract last year, for one thing.

>It is logical, and lambeosaurs were also relatively bulky.< Could I get some ratios/measurements, please?

Didn't you read The Dinosauria?

>I don't think so; it seems far more likely that hadrosaurs fled, and fought
only as a last resort. If hadrosaurs had regularly attempted to stand their
ground, weapons and or armor would have been selected for. Instead they
evolved keen senses and longer legs, and "hooves".<
Zebra don't have weapons, and still manage to not get hunted to extinction
by lions, leopards, and cheetahs.

I didn't say T. rex wiped them all out. But the advent of this predator, with its long legs and advanced senses, may have eclipsed most lambeosaurs as well as the smaller ankylosaurs and ceratopsids.

>I know; I was just pointing to the absence of such weapons as evidence for
a noncombative survival strategy.<
Or a different mode of display. I think what a lot of us think of as
defensive weapons (ceratopsian horns, etc.) may really be display (like
modern antelopes, deer, etc.), with defense as a secondary consideration.

The fact that all ceratpsids, some female, had horns suggests an antipredator role was important.

>It would have bitten into the upper thigh or flanks.< Yet the healed bite wound is on the tail...

That may not be a bite wound; Tanke and Brett-Surman disputed that interpretation.

>Not according to Bakker and Paul, see PDW. Tyrannosaurs also had the advantage of more efficient avian-like respiration.< See my first statement.

>But it lived at least 4 million years before T. rex, whose closest ancestor
must have been something like T. bataar, which was roughly contemporaneous
with the late Edmontonian fauna.<
Yet, if I'm remembering correctly, GSP suggested that Daspletosaurus was
actually a synonym Tyrannosaurus. If they are close enough to suggest they
were congeneric, could their impact have been so different.

Yes! T. rex was twice as massive, with a posteriorly expanded skull providing much more area for muscle attachment.

>If longer legs conferred no advantage, why were they selected for among
tyrannosaurs and hadrosaurs by
the Lancian? Why did T. rex monopolize the top predator niches, including
prey which fled; why didn't Albertosaurus persist like the cheetah alongside
the lion if it were faster?<
They were selected because the animals were getting bigger. No theoretical
speed increase is needed, when we can measure the increase in size in both
hadrosaurs and tyrannosaurs. The prey which was getting larger, in order to

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.

and the predators needed to either A)get bigger to be able to
continue to hunt

Albertosaurus was not the immediate ancestor of T. rex. Its ancestor must have evolved inland-as it is unknown in the Horseshoe Canyon. Finally, T. rex spread to the lowlands, displacing the albertosaurs and forcing the herbivores to become larger-those that could adapt.

B)go extinct, if the animal was already specialized in its
niche, and not able to adapt as fast.

Student of Geology
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