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Re: cause of Gigantism in sauropods



On 2/12/2011 4:20 PM, David Marjanovic wrote:

Similarly capable"? Adult Nile crocodiles are much bigger than
alligators, and it shows in the body count.

It is my understanding that 3m and even smaller crocs are extremely dangerous, and regularly stalk humans -- alligators rarely do.

Caveat -- people who are on crutches or otherwise engaged in non-bipedal terrestrial locomotion are likely at higher risk in the presence of a gator over <2m (personal observation, and Florida gator attack data 1949-1997).

Should you cite data showing that crocs only become dangerous when they are larger than gators, I will come up with another example to illustrate the larger point -- analyzing the behavior of one group is not reliably informative relative to the behavior of another physically similar group w/ unknown behavior -- especially when something as variable as aggression is the issue.

Note -- please take "crocs" here to indicate the nile variety, although other species also nicely illustrate the point.

 That said, I am also extremely skeptical of neck-as-weapon scenarios
 -- the small and fragile head was out there on the end of all those
 highly pneumaticized vertebrae and critical fluid/electrical
 transmission systems!

As has been mentioned, giraffes do it anyway.

My understanding is that giraffe-neck as club is primarily or entirely known in intra-specific combat. Apples to oranges... any devastated lions in your database? happy to hear about that should they exist.

Not that it really matters -- lions are not tall, bipedal, and have giant jaws and knife-like teeth...

If you cannot quantify dangers, you cannot tell if they made something
too risky to do.

Then why bother to speculate that the neck was too dangerous to attack?

 Rapid head swings were unlikely to part of the repertoire -- pi*10m
 =~ 31.4 m -- so roughly 10m/sec, given 3 seconds to make a half
 circle... any slower, even a giant biped could dodge the blow. The
 sauropod has serious momentum issues should it miss.

Please quantify "serious".

Tactically serious. Missing a blow leaves one open to counter-attack is my experience. Especially the roundhouse swing...

Or in the case of a downward strike, the head would likely strike the ground. Also -- please note that the number given is average speed, meant only to illustrate the high possibility of serious sauropod injury -- the real forces involved would be much higher, given an acceleration from zero, and a 3 second time frame.

 Size is heritable. If the larger sauropod individuals are culled, the
 smaller individuals pass on their genes. Size decrease in the general
 population follows. Your opening if/then statement is false, and all
 the premises you have built upon it are therefore false.

Wrong.

If the larger sauropod individuals have a higher mortality _than the smaller 
ones_,

Yeah, that is what I said. Re-read it. Or look up "culled".

then your scenario happens. Otherwise, it doesn't.

Yeah, that is why "raptorial talon"'s statement --

"If gigantism in sauropods was primarily a*response*  to predation
pressure by theropods, then theropod predation *upon large
individuals* is the*cause*  of sauropod gigantism, correct?"

is incorrect. Removing large sauropods ("culled" = "higher mortality") results in size decrease, not increase.

So -- it was not my scenario, it was raptorial talon's, and we (David and Don) agree on the evolutionary logic. Sorry you got confused about who said what, and the meaning of "culled"...

Regardless of whether adult sauropods were immune to predation, I find it 
difficult to imagine that they were _preferentially_ attacked.

I agree, given immediate availability of smaller individuals. Who said that? What a whacky idea...

That said, it was not tactically impossible in my view, given firm footing.

I do not have time to address your comments on sauropod locomotion relative to soft ground at the moment -- but I will get back to you on that. Again...