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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*) alone:

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 saber-tooth adaptation.
<<

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
 transmission systems!

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.

http://www.fanfiction.net/s/209834/1/Godzilla_vs_Cthulhu

 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_, 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.