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Re: Tyrannosaurus "Scavenger vs. Predator" debate - Some questions for Dr. Jack Horner:
Not a bad little opinion-piece. Tweak it up a bit and it would make a
great "side bar article" in a magazine. You oughta try submitting it to
_Discover_ mag., or even _Smithsonian_.
Regarding the tail-chewed hadrosaur: I'll wager you will be hearing from
Ken Carpenter soon. The specimen is in the DMNH, not the Tyrell.
On Sun, 15 Feb 2004 19:47:52 -0800 (PST) "Vlad Petnicki"
> I believe that Dr. Horner?s theory that T-Rex was
> primarily a scavenger is:
> a. contradicted by direct evidence; and
> b. fails a logical analysis that I recently
> brainstormed while taking a long drive (when I have
> traditionally done some of my best thinking). More on
> this in a moment, but first, the evidence.
> A. Direct Evidence of predation in T-Rex:
> Recently I became aware of two fossils that show
> wounds that indicate tooth marks and bite
> circumference of adult T-Rexes; in both instances the
> prey escaped and the wounds healed.
> The first is a complete Anatotitan skeleton
> (I believe it might be at the Tyrrell Museum, but don't
> quote me here - I saw photos of it on one museum site
> recently). The amazing part is a large circular bite
> that removed, in a perfect semi-circle, portions of
> several tail vertebrae, along with marks and holes
> fitting T-rex teeth perfectly. The animal's wound
> Secondly, I just recently read a description of a
> Triceratops skull with teeth marks on the frill - and
> on one broken horn; again, matching T-Rex teeth
> perfectly. Again, the animal lived and the wounds
> Several points here; with most fossils bearing T-rex
> tooth marks, it is not possible to say how the animal
> died, or what animal killed it - it is only in the very
> rare instances of grievous injury, followed by healing,
> evidenced by these two fossils, that we get a clue.
> The fact that several of these exceedingly rare fossils
> have been found would tend to suggest that this was not
> a unique occurrence.
> Now, my information is that there is no other large
> predator known from Hell Creek - except for T-rex. The
> next largest one is, I believe, a 6-foot Dromaeosaur.
> This fact indicates that T-rex is the only known animal
> that could have inflicted the wounds described above.
> This point about the Hell Creek predator records leads
> me to my second point of logical analysis, which
> occurred to me during my "brainstorm".
> B. Logical analysis of Hell Creek fauna/ecosystem;
> Since T-Rex is the only large predator known from Hell
> Creek, a problem exists for the theory of T-rex
> being an exclusive scavenger.
> For the sake of argument, let us take as correct Dr.
> Horner?s view that a T-Rex adult was too heavy, too
> slow, and too near-sighted to be anything but a
> scavenger(One question on this last point - would not
> the measurable fact that T-Rex's eyes faced forward,
> thus allowing for stereoscopic vision, contradict that
> part of Dr. Horner?s analysis?);
> So, let's look at the ecosystem it lived in.
> If T-Rex was indeed a scavenger, how is it possible
> that no (other)large "predator" is known from 100+
> years of excavating at Hell Creek? Doesn't nature
> abhor a vacuum? If T-rex was not a predatory animal in
> the main, where is that "other" "Apex predator" in this
> ecosystem? Why is that niche empty?
> Logically, a scavenger eats other animals' kills. It
> surely cannot survive by mainly waiting for prey to
> keel over from old age. But if an adult T-rex was a
> scavenger, what other animal's kills did it scavenge if
> the next largest meat-eater known from the site is a
> small Dromeaosaur?
> Let us now offer several possibilities that would get
> us out of this quandary, and perhaps to a point where
> we may come to some agreement with Dr. Horner on this
> Several recently described skeletons of sub-adult and
> juvenile Tyrannosaurids indicate that, while the main
> "weaponry" in terms of the jaws and teeth was fully
> developed early in life, the younger animals were
> lighter, with longer legs vs body ratio - in short
> built for speed.
> If T-rex was primarily a scavenger, would not these
> youngsters have starved to death because the much
> larger, older adults would have monopolized the
> carrion? They didn't, and the reason is obvious from
> their physiology. They were not scavengers. They were
> the 'Apex Predators' of that ecosystem.
> Now, we can concede the argument that adult T-Rexes may
> have relied on scavenging more than on predation, but
> they would have been scavenging the kills of their
> lighter, younger, predatory offspring. Is that the
> whole story?
> Perhaps. Since no terrestrial animal known is an
> exclusive scavenger, perhaps whether it mainly preyed
> or mainly scavenged was a factor of its period of life
> (age), rather than a factor of its species.
> A second, as yet unproved theory, is that of pack
> hunting, where the above described differences between
> individuals, based upon their age, would have fit with
> and complemented each other. We know that the giant
> Allosaurids from South America appear to have lived in
> packs (which the two Giganotosaur burial groups found
> by Dr. Coria indicate - indeed, given the size of the
> Titanosaurids down South, this makes logical sense -
> prey bigger than predator drives pack hunting; predator
> bigger than prey drives solo hunting).
> I believe that one mass Albertosaur grave was found in
> Canada, suggesting that this close relative of
> T-rex may have done likewise. Younger animals chasing
> down, tiring out, cornering larger prey, til the
> slower, more powerful adults caught up and
> killed it (or ambushed it).
> Surprisingly, this is not so far-fetched; we know that
> Crocodiles - arguably "dumber" animals than these giant
> theropods - cooperate in predation in several ways -
> several will hold an animal carcass under water while
> one twists in order to tear off chunks of the prey;
> then switching roles and taking turns 'sharing' the
> kill; also, Crocs will often corner fish in a lagoon,
> and block the only exit, then take turns, one by one,
> going into the lagoon and feeding. It is
> well-accepted, as I understand it, that small brain
> size does not necessarily prohibit complex herding or
> cooperative behavior.
> As was discussed on this site a couple of years back,
> the very end of the Cretaceous in Western North America
> has offered us some tantalizing clues as to the
> existence of potentially 15-20 ton Ceratopsians
> (Barnum's Maximum Triceratops fossil, and the
> rumored-but-yet-undescribed 9-10 foot Triceratops skull
> in the BYU basement that Dr. Bakker is familiar with
> come to mind), as well as potentially 20-30 ton
> Part of this is based on fragmentary fossil evidence,
> but also on some truly huge Ceratopsian and Hadrosaur
> tracks that have been discovered in North America.
> So, T-Rex would have had a "choice" that we have seen
> exercised everywhere else in the fossil record, where
> prey grew bigger and bigger (Africa, South America,
> Jurassic North America) - to get bigger too ? or to
> pack hunt. In any event, even an animal the size of
> the "Celeste" Rex probably could not have
> single-handedly taken on a 15 ton triceratops.
> Therefore, it is tantalizing to speculate that perhaps,
> like their distant Southern Continental cousins, T-Rex
> may also have solved this problem by cooperating and
> hunting in packs, or prides, where the animals' role in
> the hunt would be dictated by its age and size.
> These meanderings aside, if Dr. Horner wishes to defeat
> the T-Rex-as-predator argument, he must not only take
> down Prof Holtz's (and others) observations about the
> massive power of the T-Rex dentary equipment,
> suggesting predation, but he must also address the
> logical problems with his theory, when viewed from a
> "macroecosystemic" view that I have discussed above.
> In short, if T-Rex was indeed just a scavenger,
> where is the missing "Apex Predator" from Hell Creek?
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