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Re: cause of Gigantism in sauropods



On Feb 10, 2011, at 2:16 PM, Don Ohmes wrote:

> On 2/10/2011 12:34 PM, Raptorial Talon wrote:
> 
>> 1. How effective were large theropod teeth at sinking into a good
>> 10-20 cm of leathery skin?
> 
> Given a neck diameter of 1m, that implies the neck could be as much as 
> 40% skin -- even more where it is smaller.

That seems a bit thick to me, too, though I also note that quite a few sauropod 
necks were more than a meter across at the base.

>> 2. How much torque would be required to snap a large theropod's teeth
>> right out of its jaws?
> 
> What effect would such action have on the extremely high-pressure veins 
> and arteries that presumably lay somewhere between the "vertebral anvil" 
> and the knife-like teeth? Why would the theropod not simply let go, and 
> wait a bit. Any bleeding must have been dramatic. Plus, their teeth grew 
> back.

There's the rub, though - I was just looking at some large theropod specimens 
today, along with an adult Apatosaurus louisae (the holotype, actually).  Even 
if the teeth are imbedded all the way to their base, it's not altogether clear 
if they'd get deep enough to hit the primary vessels.  The vertebral aa. are 
encased in bone, and the carotids were probably located in a ventral location 
and encased in a carotid groove (as in birds) surrounded by muscle.  Veins 
might be in the line of fire, but the pressure in the veins would not be that 
excessive; the blood is basically just dripping back via gravitational 
acceleration at that point, minus the resistance of the vessel walls.  The idea 
of a bite to the neck may seem intuitively catastrophic, but a number of 
thick-necked vertebrates use them as weapons (giraffes and pinnipeds for 
example).  That's anecdotal, but I think we need to be careful not to assume 
that a long neck must be a huge vulnerability.  Limbs contain major vessels, 
too, after all - a femoral laceration can be lethal; but limbs are placed in 
harm's way regularly by many spp - the major vessels are protected by position, 
cutaneous tissue, and/or muscle.


>> Size alone doesn't mean everything, although it certainly counts;
>> armament and temperament count for a lot too. I've seen the footage of
>> lions taking down 4+ ton elephants, but not once have I heard tell of
>> lions taking on rhinos, not even the small 1.5-ton black rhinos, which
>> are known to nap in the open in the middle of lion territory.
> 
> Yes.

Absolutely; an excellent point.  By that same token, attacks on adult 
thyreophorans were probably not popular, even though they were generally much 
smaller than sauropods.

Cheers,

--MH


Michael Habib
Assistant Professor of Biology
Chatham University
Woodland Road, Pittsburgh PA  15232
Buhl Hall, Room 226A
mhabib@chatham.edu
(443) 280-0181