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RE: cause of Gigantism in sauropods



David Marjanovic wrote:

<That's completely opposite my point. My point is that most people believe all 
lions are Serengeti lions, because the Serengeti is on TV. Serengeti lions 
hardly if ever attack elephants, rarely attack buffalo, and the males just lie 
around lazily. Savuti lions _regularly_ attack elephants, and Kruger and Lake 
Manyara lions, as my first link says, _commonly_ attack adult male cape 
buffalo; at least in Kruger National Park, the male lions take over the lion's 
share of the hunting. Tsavo lions are different again.>

  That's actually what I was talking about. When you look into specific areas, 
specific prides, you see specific trends. When you generalize the packs, and 
use terms like "lions" without a regional qualifier, you're now talking about 
_ALL_ lions, or allow the reader to assume you are talking about lions as a 
whole, a group, a species, or a taxon (or what have you). "Lions" do not 
regularly attack 1) elephants, 2) buffalo, 3) humans, 4) Jackalopes, but _can_ 
and _may_ do so. The specific is characterized as unique for the whole, and 
sensationalized, because it registers as a small blip in the general plot of 
predator:prey interactions involving lions. Elephant-killing is restricted 
almost solely to smaller prey animals of the Savuti, weak, or injured. The mere 
image of equating a healthy adult bull *Loxodonta africana* in the same sense 
as an isolated, straggler *Equus grevyi* allows the viewer to generalize the 
sensational, and ignore the actual quality of the sensational as _rare_ (again, 
when applied to the bulk of lions, including those in India).

<Animals aren't planes...>

  I can model a bent plane and call it a section of a spheroid, and it will be 
just as effective. I don't get your point.

<If the serrated cutting edges on both sides of each tooth were just to somehow 
aid piercing, why are the teeth so strongly flattened labiolingually, and why 
is all of this reduced in baryonychines and lost in spinosaurines and most 
crocodyliforms?>

  This was followed with a (incredulous) "'maybe'???" in response to my 
statement that not all theropod teeth have a cutting action.

  See, now we're generalizing the specific again. "Strongly" labiolingually 
compressed teeth are a case of the specific, due to relative proportions in a 
few set of teeth. Based on the length of the tooth, the diameter of the base 
mesiodistally, the teeth of some theropods (dromaeosaurids in particular, but 
more like "unenlagiines" among them) are so strongly mediolaterally compressed 
that one would infer that such a model (pucture then pull, with posterior pull) 
would be easily reflected in this dentition. But these teeth are typically not 
serrated. Labiolingual compression can involve serration ("allosaurs") but this 
is being generalized as not all allowsaurs have all labiolingulaly compressed 
teeth, nor does a single *Allosaurus fragilis* jaw possess only labiolingually 
compressed teeth in all areas of the jaw. Mesial and distal most teeth in such 
jaws lower the aspect of compression relative to length AND mesiodistal basal 
length, but the teeth most mesial in the jaw are essentially rounded with 
inflected mesial carinae, and could NOT act in the pucture-pull model the 
remainder of the jaw can. These teeth are not often so significantly smaller 
(as in tyrannosaurids) as to be effectively separated from the remainder of the 
tooth row, indicating they are involved in the bite to some degree.

  Have you actually tallied tooth shape across theropod dinsoaurs to assess the 
quality of serration, serration angulation (it matters when biting), carinae 
position, as well as the proportions of the teeth when fitting the quoted 
argument to it (this would potentially influence phylogenentic analyses, at any 
rate)? Because I infer from your mixing of some spinosaurids with *Allosaurus* 
that you're generalizing theropods as a whole, and thus I must ask: do you 
think that such generalization is informative?

  For the record, there are more than some spinosaurid teeth that lack apparent 
longitudinal cutting actions.

<What do you mean by "double-bit"?>

  A double-bit is a reference to weapons with a cutting or striking edge on 
both sides of the haft. Why do you think many compressed theropod teeth have 
serrated _mesial_ carinae? Or for that matter, why do the D-shaped teeth of 
allosaurids, tyrannosaurids, and some smaller theropods (and even some 
sauropods) show no evidence of being effective on the pull, but are apparently 
(and anecdotally) used for the puncture alone? Both Bakker and Paul illustrate 
the premaxillary arcade of allosaurs well, exemplifying this model. The 
double-bit is a reference to a bilateral effect that contradicts a simple pull 
element to a labiolingually compressed tooth.

<Yes. What's your point with this?>

  We're discussing different teeth with different functions and the 
puncture-pull process. I am describing variations of the puncture-pull process 
that can result in variations of tooth form and arrangement.

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: Tue, 8 Feb 2011 12:30:22 +0100
> From: david.marjanovic@gmx.at
> To: dinosaur@usc.edu
> Subject: Re: cause of Gigantism in sauropods
>
> > 
> > males participate in the hunt, varies between cultures:>
> >
> > It's a trend of human psychology: To cite the sensation, unique, over
> > the characteristic, mundane.
>
> That's completely opposite my point. My point is that most people
> believe all lions are Serengeti lions, because the Serengeti is on TV.
> Serengeti lions hardly if ever attack elephants, rarely attack buffalo,
> and the males just lie around lazily. Savuti lions _regularly_ attack
> elephants, and Kruger and Lake Manyara lions, as my first link says,
> _commonly_ attack adult male cape buffalo; at least in Kruger National
> Park, the male lions take over the lion's share of the hunting. Tsavo
> lions are different again.
>
> > It is far more common to see citations of unique kill events in the
> > Savuti than it is to record the day-to-day ordinary kill events.
>
> To the contrary -- most people, it seems, still believe adult elephants
> (and hippos) are immune to predation.
>
> > Lion canines, much like leopard ones (and jaguars) are blunt for the
> > crushing bit. They even sometimes have carinae. This probably helps
> > enable the piercing bite more than the tearing action of the jaw. But
> > it is jaw strength and not tooth form that helps lions crush
> > anything; they selectively use their limbs and teeth to disable and
> > render, rather than opting one set of tools for a task (which is the
> > pattern for other big cats). This is comparable to bears, which they
> > share similarities to in canine morphology.
>
> That's what I mean: this is very different from theropods like *Allosaurus*.
> >
> > Also, the comparison of the *Allosaurus* skull as a hacksaw is
> > enormously oversimplified and, I think, inaccurate: A hacksaw's teeth
> > are arrayed in an alternating splay, effective on both a push and a
> > pull (most normal saws have special teeth that are oriented to permit
> > both, a hacksaw is designed primarily for the push stroke), while an
> > "allosaur"'s jaw is only effective on a pull. Similarly, a hacksaw
> > is ineffective when the edge of brought down on a plane,
>
> Animals aren't planes...
>
> > while this action is used to promote the image of the allosaur skull
> > as a "hatchet" (Bakker's term). This is because a theropod tooth is,
> > primarily, a piercing device (always) with a cutting edge (maybe),
>
> "Maybe"???
>
> If the serrated cutting edges on both sides of each tooth were just to
> somehow aid piercing, why are the teeth so strongly flattened
> labiolingually, and why is all of this reduced in baryonychines and lost
> in spinosaurines and most crocodyliforms?
>
> > not a double-bit edge with a blunt terminus.
>
> What do you mean by "double-bit"?
>
> > And all theropods must gain leverage with a piercing strike followed
> > by a pull -- variation tends to involve in how and in which direction
> > the pull occurs, such as leverageing with the jaw instead of the body
> > and pulling up rather than back, or altering the angle of jaw to
> > ground and pulling in the direction of the jaw from the ground
> > (lifting vertically).
>
> Yes. What's your point with this?