[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

RE: cause of Gigantism in sauropods



David Marjanovic wrote:

<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.>

Typically, clean, unworn, and undamaged sabres are serrated, at least in 
*Smilodon fatalis* and some specimens ascribed to *Dinofelis* (I think ... at 
least some sabres from southern African sabrecats, and it may instead be 
*Homotherium*). The serration quality seems to be present thus in sabres and 
dirks.

Teeth show wear of the denticles, which are globular and generally uneven, 
blobs of enamel along the distal carina (I think some are irregularly preserved 
on the mesial as well) and are wholly unlike anything in archosaurs where the 
denticles are flush with the crown surface and carina instead of "droplets" on 
the edge. Mechanically, these denticles appear more consistent with the form in 
tyrannosaurids and *Richardoestesia,* which are rectangular with slightly 
rounded apices, and are primarily adapted for holding fibers between them and 
tearing as the tooth carinae is drawn through the flesh transversally. The 
laterally-compressed sabres/dirks and those of *Richardoestesia* imply that 
these teeth were not used in the same manner as tyrannosaurids, but may rather 
have compared well with opening wounds on a puncture bite (although it should 
be noted that the cited reference by Martin, Naples and Babiarz includes 
cautionary tales of weak puncture-based capability in dirk-toothed cats, prone 
to fracturing the long teeth). Martin has compared they dirks of some sabrecats 
to the kukri, and I am inclined to agree that an assisting, lacerating 
capability as the edge is drawn along the surface of the skin would be 
extremely effective in "bleeding" the victim. Gymnastics may be required.

Cheers,

Jaime A. Headden
The Bite Stuff (site v2)
http://qilong.wordpress.com/

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)


"Ever since man first left his cave and met a stranger with a
different language and a new way of looking at things, the human race
has had a dream: to kill him, so we don't have to learn his language or
his new way of looking at things." --- Zapp Brannigan (Beast With a Billion 
Backs)





----------------------------------------
> Date: Sat, 12 Feb 2011 22:20:59 +0100
> From: david.marjanovic@gmx.at
> To: dinosaur@usc.edu
> Subject: 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.