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Re: late night thoughts: misunderstand what?

----- Original Message -----
From: "don ohmes" <d_ohmes@yahoo.com>
Sent: Thursday, June 14, 2007 3:14 PM

Granted, my comments were casual and vernacular, but other readers, if they exist, have gleaned that I am not advancing the hypothesis that *T. rex* (as you write it) personally caused the extinction of the sauropods.

A butterfly scenario to save sauropods from certain extinction is not something anyone would intuitively come up with, I thought. I obviously didn't, so I thought you were unknowingly advancing just that hypothesis, and pointed it out to you.

I spell it that way because it's an abbreviation of a scientific name. The asterisks are one of the many conventions for carrying the italics over into plain text.

Assuming they read my original post, and not your "rebuttals" of sentence fragments.

I respond that way because there's usually one argument in such a sentence fragment that requires one response, and because it makes sure I don't overlook anything. I hate it when I write an e-mail that contains, say, 5 arguments and get a response that consists of a reply to one of them written on top of the entire original.

I advanced instead a predation scenario for large carnivorous bipeds; a still-hunting strategy that exploits tactical vulnerabilities of sauropod

Fine, and I pointed out that, if it really was so easy, it would have led to immediate extinction of all sauropods that were in reach. Today I have added that its main prediction, increasing sauropod minimal size, is falsified.

consistently ignored by those who insist that running speed defines the difference between predator and scavenger,

Are there any such people except Horner?

or that sauropods were 'hard targets' due to their size.

Their size, their tails, their necks, their limbs... :-)

Other points;

"It was the other way around. First sauropods became scarce or extinct in
North America, then they reappeared, and then *T. rex* evolved. Your
scenario requires that *T. rex* appeared first, and then sauropods became
rarer and rarer and then died out." -- D Marjanovic.

1). My 'scenario', as you have defined it, does not require that *T. rex* or any functional equivalent loiter around any given geological period waiting for sauropods to appear so they can be extinguished. Quite the opposite, as the predator follows the prey in matters evolutionary. The fact that *T. rex* evolved in the presence of sauropods would tend to support an "arms race" scenario rather than falsify it.

It didn't simply evolve in the presence of sauropods, the sauropods stayed there. Both it and *Tarbosaurus* coexisted with sauropods throughout their stratigraphic occurrences, as far as we can tell.

Also, vulnerability to predation does not necessarily imply extinction, immediate or otherwise.

It does if the vulnerability is great enough, which is what you suggest.

BTW-- Re the 'first' extinction; weren't there a lot of allosaurs around about the time that occurred?

*Acrocanthosaurus*, which was no bigger than the Late Jurassic *Saurophaganax* (smaller if anything) even though bigger sauropods were available (*Sauroposeidon* vs *Brachiosaurus* -- ignoring *Amphicoelias fragillimus* for the moment). Other carcharodontosaurids of even bigger size were present in Africa (*Carcharodontosaurus*) and South America (*Giganotosaurus*), where no such sauropod extinctions happened.

2). The record of sauropods in general seems to be one of increasing size,


and the constant presence of Tall Bipeds having large toothy Jaws (TBJ's)-- bipeds just tall enough to reach their necks.

Sometimes much taller. http://www.luisrey.ndtilda.co.uk/html/holtz07.htm Scroll down to "Before and After"; in "Before" you have an adult *Amargasaurus*.

Does the way the sauropod record fizzled out (in terms of diversity)

Did it fizzle out? Sure, we seem to have only titanosaurs at the end, but the titanosaurs themselves are so diverse in shape and size...

"Tyrannosaurids don't look at all like specialized sauropod-hunters. From
such an animal I'd expect the ability to make huge wounds in a short time
and then retreat. This is what carnosaurs, especially carcharodontosaurids,
look like. Tyrannosaurs were pursuit-and-bite predators." --D Marjanovic.

3). Why specialized? Why can't they hang out and eat whatever walks by? Why 'huge wounds', and 'retreat'? Why would you expect that? I always thought "jaws big enough to crush the neck", and "tall enough to reach it" was kind of hard to ignore as a possible outcome/workable strategy. Why risk attacking the body when you have a bite-size, crunchable 10m bundle of vital nerves and arteries/veins right in front of your nose?

Because they are most likely not right in front of your nose. So why bother when you can slit the leg muscles through, for example? Even lions don't bother killing elephants before eating them.

How much leverage do you have when you get a bulldog grip on any point of the distal 2/3 of a 10m neck, if you weigh over 4000kg? How much weight could you tie to a sauropods head before the neck buckled? Less than the weight of a tall large-jawed biped, I bet. (*T. rex* were _bite-and-hold_ predators from the looks of the teeth, BTW. Not pursuit-and-bite.)

Pursuit, bite, and then hold. Look at those legs... and/or read Holtz 1994/1995.

"Sauropods don't run away, and staying to fight with a sauropod is ill-advised." --D Marjanovic.

4). Well if they don't run away, no need for pursuit. Why not fight a sauropod? What is ill-advised? Lot of food there. What's he going to do, sit on you?

Just about any way it moves, if it hits you hard enough, you have a problem. And if it doesn't move and dies right away, you have another problem because it could fall on you.

Life-dinner principle: predators take much less risk than prey.

If he rears up and paws at you, so what?

If he hits you, you fall over and could break your own neck, for example.

What is the lifespan of a sauropod w/ his neck between the jaws of a TBJ? 5 seconds, or maybe 10?

(This applies to tyrannosaurids, but not to allosauroids, which had weak bites.)

5). [...] Do you think sauropods could effectively monitor the area on either side of the proximal half of the neck while locating, picking, and ingesting that 'no-swallowing, steady-stream' of forage certain people hypothesize?

Sure. The eyes are always the highest spot of the head. This is most extreme in the ground-feeders like *Nigersaurus*. Have you seen the reconstruction of its skull? It's grotesque. The orbits are caudodorsal to the temporal fenestrae.

"And there's no evidence for an arms race... " -- D. M.

6). Aw c'mon! They were HUGE. What else?

Science is a lot of work.