RE: cause of Gigantism in sauropods

[Jaime Headden <qi_leong@hotmail.com>]

  *Tyrannosaurus rex* has been called "heterodont by some authors, an allusion 
not only to the ziphodont crowns of the typical jaw margins and the D-shaped 
premax teeth, but also to the lower-crowned, broad teeth in the rear of the 
jaws. These latter teeth show less recurvature and blunter apices than other 
teeth in the jaws excepting the "incisiforms" of the premaxillae, and were 
suggested by some authors of relating to bone-crushing. Similar teeth, although 
much more incrassate, are found in living crocodilians, some of which lack the 
morphology but others (such as *Alligator mississippiensis*) showing an extreme 
form of it. This has been linked to their increased durophagous behavior over, 
say, more "flesh-eating" *Crocodilus niloticus*. 

  But I have never heard of a primary bone-crushing manner of dispatching prey, 
nor with the brevity of such exapted teeth in the rear only portions of the jaw 
do I think that *Tyrannosaurus rex* could have employed a crushing-bite method 
so easily. Because of their position in crocodilians and blunt-toothed lizards 
(*Varanus exanthematicus* as well, also durophagous), specialized care in 
processing is usually done to select foods (turtles in the crocs, gastropods 
and even eggs in the lizards) and in a precise manner (they are "handled" into 
position). I can see this behavior as an extension of carcass-stripping and 
marrow-scavenging, but not as a primary dispatching method.

  Despite this, tyrannosaurids all still seem pretty head-dominated as adults, 
so much so that their jaws WERE the primary tool of killing, as they pretty 
much lacked any other. My off the cuff impression is that of jaw-based 
grappling and then disabling through progressively more grievous wounds. Horner 
can even have his say here as a tyrannosaur can spend a day or two (as wolves 
can do) following previously injured prey in order to ensure it keeps the 
eventual kill. None of this requires "slash-and-burn" as inferred for 
*Allosaurus*/*Carnotaurus*. However, I am glad to be wrong on this, as I also 
suspect *Tyrannosaurus rex* may have occasionally used the leopard strategy: A 
precise crushing bite to the skull -- this way, Dan's suggesting can be true as 
well.

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)





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> Date: Fri, 11 Feb 2011 11:17:40 -0700
> From: danchure@easilink.com
> To: rtravsky@uwyo.edu
> CC: dinosaur@usc.edu
> Subject: Re: cause of Gigantism in sauropods
>
> Or just crushing of bone?
>
> Dan
>
>
> On 2/11/2011 10:26 AM, Richard W. Travsky wrote:
> >
> > On Thu, 10 Feb 2011, Habib, Michael wrote:
> >> On Feb 10, 2011, at 2:16 PM, Don Ohmes wrote:
> >>
> >>> On 2/10/2011 12:34 PM, Raptorial Talon wrote:
> >>> [...]
> >> There's the rub, though - I was just looking at some large theropod
> >> specimens today, along with an adult Apatosaurus louisae (the
> >> holotype, actually). Even if the teeth are imbedded all the way to
> >> their base, it's not altogether clear if they'd get deep enough to
> >> hit the primary vessels. The vertebral aa. are encased in bone, and
> >> the carotids were probably located in a ventral location and encased
> >> in a carotid groove (as in birds) surrounded by muscle. Veins might
> >> be in the line of fire, but the pressure in the veins would not be
> >> that excessive; the blood is basically just dripping back via
> >> gravitational acceleration at that point, minus the resistance of the
> >> vessel walls. The idea of a bite to the neck may seem intuitively
> >> catastrophic, but a number of thick-necked vertebrates use them as
> >> weapons (giraffes and pinnipeds for example). That's anecdotal, but I
> >> think we need to be careful not to assume that a
> >
> > What about the windpipe and suffocation?
> >
> >> [...]
> >
> >
>
>