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Re: cause of Gigantism in sauropods
Long, combined response to posts as old as Feb. 8th.
> Try saber-toothed cats instead, in particular the cookie cutter
> cat *Xenosmilus* (...and apparently the non-cat *Barbourofelis*).
> I'm trying to say the strategy of killing by inflicting random
> bleeding large wounds looks scaleable to me.
Um, would you be implying that sabertooths hunted by inflicting large
bleeding wounds with random slashing attacks? Because that would have
snapped the teeth out of their skulls right quick . . . a precision
"shear bite" to the trachea and surrounding blood vessels is much
more likely, with the massively developed forequarters of such
predators being used to hold prey as still as possible to avoid the
torque that would otherwise easily damage the teeth.
Sorry. Dirk-toothed cats most likely hunted the way you describe. I
should have talked about *Xenosmilus* (and apparently *Barbourofelis*)
Larry Martin, Virginia Naples & John Babiarz (2008): Cookie-cutter cats;
another saber-toothed morphotype, supplement to JVP 28(3), 112A
L. D. Martin proposed that all cat-like carnivorans could be placed in
one of three morphotypes: conical-toothed, dirk-toothed and
scimitar-toothed. All modern cats are conical-toothed. The other two
types have blade-like canines (saber-tooths). The dirktooths had shorter
legs than do ordinary cats, while the legs of the scimitar-tooths are
more elongated. Dirk-toothed forms ambushed their prey, while
scimitar-tooths must have engaged in pursuit. We think that the
dirk-toothed forms killed using a highly specialized throat bite, but
that scimitar-toothed forms may have bitten prey in a variety of
locations. Their canines were shorter, broader, more coarsely serrated
and nearly continuous with the incisor arcade. These features are most
prominent in *Xenosmilus*, a newly described Pleistocene form that
breaks the paradigm by combining scimitar sabers with the short limbs of
an ambush predator. In *Xenosmilus*, the sharp, prognathous incisor
arcade coupled with the canines could have cut out a lump of flesh about
as big as the cat could swallow. Such terrible bites would have quickly
put the prey into shock. Death might have resulted from multiple wounds
rather than through a directed killing bite, although these cats could
make such a bite if the opportunity presented itself. This bite would
resemble the action of a cookie cutter taking out a section of dough,
and we have used that example to provide a name for this unusual
I was there and gazed at the poster. The skull is hard to believe. Not
only the upper canines, but also the lower ones, and all incisors, are
serrated. The incisors are large, and the canines are actually rather
small for a sabertooth (no comparison to *Smilodon*). That's by far the
closest to a standard-issue theropod that mammals have ever got.
This implies a couple of things about prey size, I think. To take out
the prey's carotids, jugulars and/or trachea, like dirk-toothed cats
apparently did, you need to be able to get something like 2/3 of the
prey's neck depth into your mouth. Cookie-cutter cats had no such
requirement; their mouths only needed to be big enough to make the prey
bleed and hurt seriously.
Although I do think the random bleeding wounds hypothesis actually
may hold for at least some large theropods, especially since large
canids hunt this way to some extent and they're closer in gross skull
morphology than are big felids.
Canids are very poorly equipped for it, though. They have conical
canines without cutting edges, let alone serrations. I once watched a
wolf pack kill a bison on TV. Or, rather, most of it was cut out, not
just because of how cruel it was (that still came across), but because
of how long it took: several hours. The wolves tried to fell the bison
by exhausting it and tearing its anal region, where the skin is thinner,
to shreds that hung off the animal. They can pierce and tear, but not
cut. It's pathetic!
Alligators are tactically capable of eating people, but statistically
rarely do -- taking that data to form a null hypothesis about the
behavior of the similarly capable Nile Crocodile, or even individual
alligators, is unlikely to prove useful.
"Similarly capable"? Adult Nile crocodiles are much bigger than
alligators, and it shows in the body count.
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
As has been mentioned, giraffes do it anyway.
If you cannot quantify dangers, you cannot tell if they made something
too risky to do.
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".
Also -- tactically, it is logical that a giant biped that attacked a
giant quad in an area where preservation was likely to occur (i.e., a
swamp), would BE the fossil... albeit a flat one.
It quickly ceases to be logical when you look at the feet.
Theropods: long, somewhat spread toes.
Sauropods: feet like column fundaments, hands like columns.
There's a reason why the hypothesis that sauropods 1) lived in swamps
and 2) theropods weren't able to go there was abandoned in the late
1970s, some 35 years ago.
Also, Godzilla doesn't just go down to Cthulhu. True fact.
That's what you think.
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.
If the larger sauropod individuals have a higher mortality _than the
smaller ones_, then your scenario happens. Otherwise, it doesn't.
Regardless of whether adult sauropods were immune to predation, I find
it difficult to imagine that they were _preferentially_ attacked.