Scavengers and Hunters, Part I

Greetings! I have been following the popular press and media on this topic (not having access to a lot of peer-reviewed materials…) I have an observation regarding this topic that I have not previously heard or read about.

What about intraspecies aggression? I have heard that the remains of several T rexes - I don’t know which ones, but I believe “Stan” had his head nearly bitten off, didn’t he? - showed evidence of traumatic injuries which were, apparently, inflicted by other tyrannosaurs. If this is not the case, I am mistaken and apologize.

If this IS the case, however, I would think that the apparent fact that T rex individuals fought and possibly killed each other, for whatever reason, obviates the argument that they were incapable of actively predating upon other species. Compared to fighting another T rex, I would think that taking down an Edmontosaurus or a Triceratops would be child’s play…

Anyway, I thought I would bounce that idea off you, and see what you think.

Let me know - thanks!

Wes Copas

Interesting thought. Yes, I think there is some evidence of intraspecific aggression in T. rex.

But I don’t think that’s a direct indicator of predation. For one thing, intraspecific aggression in extant tetrapods does not usually involving running. Two individuals face each other, and one eventually backs down. When the loser runs, there is usually not much in the way of pursuit.

Secondly, intraspecific aggression does not usually lead to death. The goal is to establish dominance, not to kill. (There are certainly plenty of exceptions, though.)

Finally, many non-predators engage in similar behavior: horses nipping each other, etc. (Although I’m not sure if vultures ever bite each other—that would be interesting to find out.)

So I think it would show that T. rex were capable of attacking each other, but would not have that much bearing on their ability to kill other dinosaurs. That’s just my off-the-cuff take, though.

Not to be argumentative here, but my point was not that there is a DIRECT link between intraspecies aggression and active predation, especially among dinosaurs. However, one of the arguments I have heard over and over (in the popular press) is that the wimpy little arms, and the (perceived) ungainly build of the T rex, indicates that the beastie COULDN’T kill other dinosaurs. I think I remember a quote that went something like, “I guess he could have KICKED it over…” Another argument that was made along similar lines is that, had T rex tripped in an active pursuit, the skull would have been shattered by the force of the fall.

My point is that if the tyrannosaurs were capable of fighting each other and doing such terrible damage, they would have been capable of acrrying out aggression against other species less well-armed. If I remember what I was told correctly, “Stan” was bitten in the back of the head and neck - this would be a killing bite, not a feeding one, wouldn’t it?

I am not an expert on vulturine behavior, but I have watched them feeding in real life (I live in rural south Texas, and we see them all the time), and I have seen many documentaries wherein entire feeding sequences can be piced together. Our turkey buzzards squawk and mock-charge each other, but I have never seen an attack carried to the extent of physical contact. Others who know more can probably provide better information, but the fact is that these birds are not equipped, physically or temperamentally, for serious physical combat. They are the only pure scavengers I know of in the vertebrate world; other “scavengers” such as hyenas, jackals, coyotes, crocodilians, etc., are all active predators when the opportunity arises.

I guess the point is really pretty well settled, but I thought that perhaps the capabilities implicit in such acts of intraspecies aggression might counter some of the statements that T rex “couldn’t” have been an active predator.

Wes

Well, if your point is that intraspecific aggression supports the idea that T. rex was not a total wuss, then I agree.

Seriously, though, it would be interesting to do a broad survey of extant tetrapod species comparing violence in intraspecific aggression vs. violence in food acquisition. Perhaps there is a statistical link; who knows?

That was, in fact, pretty much what I was trying to say. I have stood in front of “Sue” while she was on exhibit in San Antonio last year, and “wuss” is the last thing that might have crossed my mind as I looked up at that maw…

Anyway, it was an observation I had not seen or heard of before, and I thought I would ask the opinion of an authority. As a paleoanthropologist by training if not actual vocation, I can warn anyone who wants to listen and/or read of the dangers of trying to extrapolate behavior from inadequate evidence…

As far as your thoughts regarding extant tetrapods (I think that could be extended to vertebrates in general, too - gotta remember the birds, and the hominids!), I would expect some correlation between the two types of violence, but I have no documentation to back myself up. Anybody out there looking for a dissertation topic?

Anyway, I’m glad we are agreed that T rex wasn’t a wuss…

Wes

I sure wouldn’t fight one.

My pedantic note of the day: birds and hominids are tetrapods; what they are not is quadrupeds. (Well, non-hominin hominids are, generally. . . .) One’s a clade, t’other is a locomotion-based category.

As for capping the study at Tetrapoda vs. Vertebrata, I suppose it’s rather arbitrary: heh, why not all of Metazoa, really? (Of course, now this has become an interdisciplinary team project rather than a dissertation. . . .)

Oh, and I’m flattered, but I think I’m a few degrees shy of “authority”; maybe just “knowledgeable enthusiast”.

Oops. Well, obviously you are more of an authority than I am; when I was “gettng my degrees” to be an authority in hominid paleontology (didn’t make it all the way), cladistics were the new science on the block, and only beginning to be taken seriously. Concepts like synapomorphy and automorphy were buzz-words from another language, and professors tended to avoid them… That was 20 year ago. “Tetra” = four or fourth; “pod” = feet… If that had been invented then, I didn’t know about it.

In the world of paleoanthropology, dissertations are generally multidisciplinary, as they must be in vertebrate paleontology. Gotta know taphonomy, sedimentology, anatomy, cladistics (which rhymes beautifully with “sadistics” and “statistics,” another arbitrary distinction), geochronolgical methods, etc. - all that along with whom to kiss and where. That’s part of the reason I only got to the Master’s thesis and decided that I would rather stay married.

Anyway, I think we might be agreed in principle about the degree of bad*ss-ness of our subject; I would not care to take one on, either, without an M-1A Abrams Main Battle Tank wrapped around me…
OBTW-You, and your discussion, were recommended to me as follows:

If you start the conversation on Keesey’s blog, you’ll be starting with someone who knows a lot, has thought a lot about it, and most importantly has already started the conversation.

If that doesn’t make you an authority, as I said earlier, it makes you more of one than I am. Think of me as a child dinosaur fanatic who just never grew up. I only know enough to make me dangerous to myself.

I have enjoyed this conversation - my first-ever blog activity. I am learning as I go, so please forgive any misdemeanors I may have committed.

Wes

Tetrapoda was actually named by Haworth in 1825, so it’s been around a while. Traditionally it hasn’t usually been given of the “Big Seven” Linnaean ranks, so that may be why you haven’t heard of it. More recently, there have been some differing opinions as to how it should be explicitly defined: some think it should be limited to the “crown clade”, that is, the last common ancestor of the extant forms (lissamphibians and amniotes), plus all descendants thereof, while others favor a broader, more traditional usage, including forms like Ichthyostega, Acanthostega, etc. In either case, though, the extant composition is the same.

(Incidentally, cladistic Hominidae now generally includes the great apes as well, with Homininae covering African forms [Gorilla, Homo, Pan] and Hominini covering everything sharing more recent ancestry with Homo than with other extant hominid genera. Thus, where they once said “hominid”, they now say “hominin”. Fun, huh?)

Yeah, working in paleontology requires all of those, too. I have one paleontologist friend who has three Bachelor’s—biology, zoology, geology—and got his Master’s in biochemistry! (Me, I just have a B.A. in Visual Arts, and I work mostly as a programmer, apart from one stint as a paleo-technician.)

Ah, nice to be recommended. And this is the sort of exchange I’m hoping for on this site, so cool!

Yes, I have noticed the linguistic shift. I did not use the term “hominid” loosely, as the “other” hominids which have been added to the clade share many more behaviors, including the originally mentioned intraspecies violence AND predatory behavior, which we were originally discussing. Many of the “old guard” still refer to humans and their immediate ancestral forms (and related populations) as hominids in the old sense, though.

I look forward to the next Hegelian turn of the wheel. Paleotaxonomic “splitting” is all well and good, but with every new (and old) fossil being assigned its own genus (or, at the very least, species), it don’t make no sense. A good dose of “lumping” will clear the muddy waters… I suppose the same is true of nomenclature in other paleospecies; however, I have read of more primitive specimens of T rex being compared to later, more advanced individuals (cladistically speaking); imagine what would happen in such a case were it a hominin taxon…

Wes

Here’s a little thing I wrote against paleotaxonomic splitting: Use of Genera. (Take careful note of the date on that, though.)

It’s true, though—these days it seems like every fossil dinosaur species has to have its own genus. To be fair, “genus” is a completely subjective rank, but still. . . .

Personally, I’m still waiting for someone to tell me what a species is. There are dozens of species concepts. Few, if any are applicable to all organisms. Few, if any, are explicit enough to be applied objectively.

I use trivial nomina because everyone else does, but for now I’m of the minority opinion that there is no such thing as a species in nature.

But now we’ve drifted very far from dinky little carnotaurin arms….

Genetic drift…?

If this conversation would be better continued in private email, I would very much like to do so. I believe you have access to my email address…? Again, I apologize for not following guidelines if I have violated the rules.

You raise an interesting point about carnotaur arms. There were other species of therapods with relatively small arms, were there not (other than tyrannosaurids)? Are the scavenger-only crowd generalizing their claims to other paleospecies as well? (See, I brought it back on topic…)

Wes

Memetic drift!

I think a conversation’s fine here—that way anyone else is free to jump in. There’s no real rules for comments, although I might see my way to deleting obscene and/or offensive comments should they ever crop up (so far so good).

Reduced forelimb size is a trend seen over and over again in large terrestrial theropods: ceratosauroids (especially carnotaurines), spinosauroids, allosauroids (especially carcharodontosaurids), tyrannosaurids, ratites, phorusrhachids, diatrymatids, etc. There are some exceptions, of course, notably Deinocheirus (an ornithomimosaur) and therizinosaurids. Interestingly, the small-armed forms also have large skulls, and the large-armed forms all have small skulls. (Well, okay, ratites are an exception, with small forelimbs and small heads—and, just our luck, they’re the only extant ones!) So it is quite possible that forelimbs were reduced to counterbalance a large head. (More on that tomorrow….)

As for the scavenger-only “crowd”, it pretty much consists of Jack Horner (and sometimes I have trouble believing that even he actually believes it), and so far he has only commented on Tyrannosaurus rex, to my knowledge. Every single other researcher I know of considers Tyrannosaurus rex to be a scavenger and a hunter. That’s why I get so tired of these dadgum slow-news-day articles cropping up all the time!

Well, then there are the two British gentelmen who were featured in the Discovery/Science Channel show about T rex… You know, the ones who did the analysis on how much biomass a scavenging T rex would require to sustain itself, and used REPTILIAN metabolic rates for their calculations…?

In a larger sense, one of the problems for us common folks who are somewhat educated but do not have access to major University library resources is that the only easy access we have to “research” is the Tube… It’s awfully hard to tell the good science from the bad sometimes. Other times, it’s pretty easy to tell… (reptilian…?)

Anyway, I also agree that it would be neat if somebody else would join our little discussion. Maybe the point is so moot that nobody feels the need to comment…? I’m good to go as long as you’ll let me, and I’m learning a lot just trying to keep up with the “new” terminology.

Wes

I should have said “every single other researcher working on Mesozoic dinosars”—I can’t recall that study right now, but I doubt anyone familiar with Mesozoic dinosaur research would assume such a thing.

I don’t watch TV much, but when I do see the documentaries they show I want to wring some necks (or maybe bite some heads…)—not just for dino-documentaries, but on other topics as well.

Well, hope you stick around here for further discussions!

Well, I read Dr. Carpenter’s paper, which he mentioned in the DML recently. The _Edmontosaurus_ argument is quite convincing… Even if it was some other large theropod which attacked the subject animal, it was probably still a tyrannosaurid, no?

Wimpy arms and all, you can’t argue with that bit of evidence (pardon the pun)

Wes

I quite agree. Well, there are no other large (let alone gigantic) predators known from the late Maastrichtian of North America besides T. rex. The only possible exception is Nanotyrannus/Tyrannosaurus lancensis, which is certainly a tyrannosaurine, and possibly synonymous with T. rex.

You mean I used _another_ outdated _nomen_?

AARGH! I guess I’m the dinosaur here…

Oh, well…

What, “tyrannosaurid”? That’s not outdated—I was just being more specific. Hehe.

At least I used two _n_’s…