Re: late night thoughts: misunderstand what?

[don ohmes <d_ohmes@yahoo.com>]

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. Assuming they 
read my original post, and not your "rebuttals" of sentence fragments. I 
advanced instead a predation scenario for large carnivorous bipeds; a 
still-hunting strategy that exploits tactical vulnerabilities of sauropod 
consistently ignored by those who insist that running speed defines the 
difference between predator and scavenger, or that sauropods were 'hard 
targets' due to their size.

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

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

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. I don't see that size increase driven by 
the necessity of keeping those necks out of reach can be ruled out on the basis 
of fossil evidence. Does the way the sauropod record fizzled out (in terms of 
diversity) falsify the notion that no matter how big a given long-neck got, the 
bipeds just got taller, and the TBJ's finally 'won'? No way. Is such an 
'victory' confirmed? I wouldn't say that, either. I'd call it a reasonable 
speculation, though.

"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? 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.)

"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? He 
might hurt you w/ a headbutt if you are really, really slow, but he would kill 
himself in the process, or knock himself out. Slap you with his tail? What 
happened to the perfectly spaced, ideal forage trees that are the "parsimonious 
hypothesis" whenever acquisition of food by sauropods is the topic? Do such 
trees fold out of the way for a good tail swing? Ever try to swing a bullwhip, 
or a rope, in brush or trees? 

If he rears up and paws at you, so what? Time he has been forced by feints and 
false charges to do that a few times, he will be too tired to hold his head up, 
and that is if he doesn't pass out from lack of blood to the brain, as some 
hypothesize. What happens then? What is the lifespan of a sauropod w/ his neck 
between the jaws of a TBJ? 5 seconds, or maybe 10?

Maybe on flat level ground, w/ no impeding vegetation, a sauropod could hold 
out for a while against a single attacker. Until it got tired. But defend 
itself against an ambush from a multi-ton mega-pitbull? In trees? Forget about 
it...

5). Why even bother to fight a sauropod?  Do you posit that sauropods kept 
'banker's hours'? Elephants forage as much as 22h out of the day. If an 
elephant's brain was out on the end of his trunk, do you think lions would eat 
them as they foraged? Night and day foraging implies a visual compromise, and 
constant, slow, pre-occupied movement through fresh territory. Do you think 
foraging sauropods never bumped noses w/ a TBJ big enough to engulf their 
entire head? 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? If something w/ a velocity of (x) charged the mid-point of the 
neck from the side, how fast would the sauropods head be traveling if it 
matched that speed to avoid the attack? Two times (x), right? Aren't there 
trees around him, by definition? Wouldn't he run his head into a tree? Have you 
ever tried
 to maneuver something 10m long through the woods? It is a slow-to-impossible 
process, critically dependent on high variable local conditions, w/ much 
backing and turning and picking of routes. And that is just the neck. The whole 
body is much longer.

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

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

----- Original Message ----
From: David Marjanovic <david.marjanovic@gmx.at>
To: DML <dinosaur@usc.edu>
Sent: Wednesday, June 13, 2007 6:13:39 PM
Subject: Re: late night thoughts: misunderstand what?

> Would you mind being more specific about what I misunderstand?

Sure:

>> I understand that consensus is that when T. rex proper was in full flower
>> sauropods were getting kind of scarce... might have been one 
>> prey/predator
>> race where the predator won.

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.

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

Furthermore, the geographical overlap of tyrannosaurids and sauropods is 
limited.

And there's no evidence for an arms race...