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Re: cause of Gigantism in sauropods



> Given a neck diameter of 1m, that implies the neck >could be as much as 40%
> skin -- even more where it is smaller.

Really, skin thickness is just a proxy for skin durability here,
whereas scales could modify any such assumptions significantly. Not
that some extra protection around the area couldn't have been selected
for in terms of sheer dermal bulk.

> 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?

If the skin itself is exerting significant resistance to the
penetration of the teeth, then I don't see how this is relevant. Any
animal has to be able to take occasional jostling, whether for mate
competition, mating itself, simple accidents, or dealing with
predators. If sudden, brief pressure without actual penetration of the
vessels themselves were notably threatening to a sauropod, then it
seems to me a firm chokehold with gripping teeth would make more sense
than the more slicing-oriented morphology we see in most large
theropod teeth.

Obviously this is working from the assumption that the skin itself was
a significant impediment to penetration/tearing, but that is what this
whole line of thought is derived from, so I'll run with it for now.

>Why would the theropod not simply let go, and wait a >bit.

You mean in contrast to a wrap-the-mouth-around-the-neck insta-kill
scenario? If the theropod can just use canid-style "bite-and-back-off"
harrying, why not land attacks more opportunistically instead of
targeting the neck? Many small, sporadic, unpredictable bites followed
by rapid retreat is more sensible than a full-on commitment to lodging
onto something many times your own mass. Also, it's something
blade-like teeth seem well-suited to.

> Any bleeding must have been dramatic.

Assuming serious penetration, yes.

>Plus, their teeth grew back.

But losing a majority of them at once would be bad, especially if the
surrounding bone itself were wrenched with them. Besides, that was
just one way of expressing the question. The potential injuries to the
skull and more especially the mandible could be crippling, too.

> Still sounds less dangerous and less likely than >falling while running
> fulltilt after smaller faster prey.

And when would that happen, exactly? Using the Morrison as an example,
juvenile sauropods and stegosaurs would not have been speeding around
like gazelles from ceratosaurs or allosaurs. They had stumpy little
legs to contend with the strides of 8-meter-long theropods. Running
wouldn't even be necessary for the predator; a brisk walk would do for
at least a sizable minority of available prey items.

>Especially given that simply harassing a
> giant sauropod for 2 or 3 days might get you a huge >happy meal w/out a bite
> fired, so to speak.

Or get you dislocated, fractured, or crushed to a bloody pulp by neck,
tail, shoulder, or what have you, especially if sauropods defended
themselves collectively as herds. You can't keep track of every tail
and foot at once, making dashing at a target very risky. And if the
target is already isolated, it's quite likely sick or injured anyway,
and with a sauropod's metabolic requirements it's not going to last
much longer regardless. So why not wait it out, maybe go in for some
modest harassment at most? Not worth the risk.

> 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!

I'm not talking about whipping the head around like a medieval flail,
I'm talking about using the ostensibly vulnerable base of the neck as
an extension for a body slam emphasizing the shoulders. The feet need
not even leave the ground - just a massive shove or pull with the
forequarters, the proximal part of the neck included. That's a lot of
momentum to absorb when you weigh a fraction of the thing slamming
into you, and the potential for wrenching your jaw or neck from a
sudden movement away would be serious if the skin in that region were
thick, heavily scaled, or otherwise resistant to
stabbing/slicing/whatever.

I seem to recall some mention of sizable neck ribs in that area a
while back; if true, that would further reinforce it against such
threats.

> a) Given a hold near the base, the "head velocities" implied by any movement
> or flailing that could exert force on the base of an 8m-10m neck are pretty
> damned extreme. This could drastically affect >circulation and balance -- and
> any collision (with a tree branch, the ground, or even the theropod) would
> be severe.
>
> 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. It just does not seem workable in any sense
> other than a straight pull back with the main body, and what good would that
> do?

Again, slamming the forequarters into the attacker would impart a very
substantial amount of momentum. Someone should make a couple of big
flesh-consistency models and whack them into each other. Even if only
fleshy tissues were being damaged - i.e. bruised to the point of being
split open - the risk of infection alone would select against that
kind of behavior as a regular part of the predation toolkit.

> b) Given a hold anywhere near the head, the >mechanical advantage is such
> that the force required to move a biting theropod >would be horrendous -- the
> neckskin distal to the torso could only be so thick, >and nerves might be
> crushed by the bite -- talk about "command and >control center" disruption...

Near the head, sure, but I thought the whole point was that the head
was aloft (or sweeping away defensively) and that the base of the neck
was the prime target in terms of "availability" as it were.

> If you can find and catch enough of them...

Titanosaur nests have what, 200 eggs a clutch in some cases?
Regardless, the evidence that they were dedicated r-strategists is
compelling, and dinosaurs overall were much more r-oriented than most
modern mammals because of the whole egg-versus-womb issue. During the
seasonal hatch (the sauropod arribada, if you will), the glut of
hatchlings would have been enormous, and even big theropods probably
could have caught enough of the helpless critters quickly enough when
they were first emerging out into the open to make it worth their
metabolic while. The ability to stock up on easy calories once a year
to help put on fat and weather the leaner season would have reduced
pressure to make risky attempts on the adults/large subadults.

Given that sauropods also took at least several years to reach truly
large sizes, there would also have been moderate-sized individuals of
different generations available at all times of the year, and there's
no biomechanical evidence to suggest that these columnar, graviportal
juveniles were faster than the large theropods in their environment.
They would thus have made easier targets, and attrition rates would
have been high, although hypothetically mitigated somewhat by any herd
behavior.

Also, IIRC, stegosaurs were the next-most common herbivores in many
Late Jurassic environments, at the very least, and the young of these
- while more prickly - would have been little faster. Adults of the
larger iguanodontians probably weren't all that much faster than large
theropods, either (no direct analysis of this that I'm aware of, other
than tyrannosaur vs hadrosaur which favors the former for top speed),
so while I wouldn't expect sprints after dryosaurs to be very common,
the occasional snagging of a camptosaur at a watering hole seems very
plausible.

When we get into abelisaurs, just what the hell they were hunting with
their weirdly proportioned skulls begs even more questions, and I have
serious reservations about the idea that their skull morphology had
anything to do with taking out even small adult sauropods, despite
being the top predators in their ecosystems during the Late
Cretaceous.

In other words, it would seem that a lot of plausible prey items
besides large sauropods were present in these ecosystems. The observed
reality in modern ecosystems, both terrestrial and aquatic,
transcending phylogeny, morphology, and hunting style, is that the
largest prey species are hunted by the largest carnivores less
frequently than mid-sized prey species are hunted by the largest
carnivores. In the case of things like elephants and rhinos, *much*
less frequently. We can talk about rare exceptions, like wolf packs
that specialize on moose or elk where whitetails are available, but
exceptions don't disprove broad trends (*cough*snowdrifts*cough*). Or
we can talk about lions being technically capable of going after
elephants, but let's not forget that hyenas, leopards, and hunting
dogs - AFAIK - *never* go after adult elephants. So by analogy, maybe
torvosaurs went after adult sauropods sometimes, but allosaurs and
ceratosaurs were cut from a different cloth and pursued very different
lifestyles.

Modern ecology is our best guide here, and I see no reason for just-so
stories to preempt multiple consistent lines of evidence suggesting
that such behavior was unlikely/rare.