RE: Microraptor Wings (and sauropods(

[Jaime Headden <qi_leong@hotmail.com>]

  You know, while my joking response was a bit ... tongue in cheek ... the 
serious response to this is oddly not that much different.

  The robusticity of the tooth or its shape is only one aspect of sauropod jaw 
strength: Most of this is based on the mandibular form itself, and there are 
several good proxies for assessing this in sauropods:

  1. Deep rostra usually indicate that at the level of biting, the jaw is 
capable of exerting strong dorsoventral compressive forces, and thus less 
mechanical bending during the bite: we see this in the tips of diplodocoid 
jaws, and to a slightly lesser degree in "brachiosaurid" (or rather, "basal 
camarasauromorphan") jaws. Regardless of the tooth shape or size, the strong 
development of the "chin" indicates an anteriorized bite, and this simply 
matches clustering of the dentition into a continuous margin.

  2. Expansion of the "coronoid process" in sauropods. Although sauropods lack 
an actual ornithischian-like "coronoid process," they do possess an expansion 
that anchors the same muscles, located almost exclusively on the surangular, 
which causes a small "peak" near the dentary articulation. The height of this 
region and relief of the scarring for the temporalis musculature groups that 
are anchored to this region indicate a developed jaw-closing/jaw-retracting 
component of the jaw. The angle of divergence of this axis of jaw closing from 
that of the pterygoideus group (the other jaw-closing muscles of note) help 
exaggerate the bite mechanics, and can tell us about differential bite 
performance when one muscle group is preferred over another.

  3. The development of the pterygoideus muscle group scars or relief on the 
ventral, ventromedial, and ventrolateral sides of the postdentary bones are 
usually indicated by the "surangular ridge," which indicates how anterior this 
muscle group goes. In most sauropods, this is very low on the lateral surface 
of the mandible, and is located primarily around and slightly anterior to the 
jaw articulation. Such a position offers the pterygoideus a mandibular rotation 
component, and can help partially protract or retract the jaw during the bite.

  4. These component jaw movements apart from the actual vertical bite can be 
secondarily indicated by wear features in the teeth, but also in the shape and 
boundary bones of the articular glenoid of the mandible, and its specific 
shape, which will show whether the jaws was capable of any propalinal or 
transverse movement. Such things indicate greater complexity in sauropod biting 
than simply _biting_. AND THEN you can get to specific features of the teeth, 
such as the close-spacing (or lack of spacing), the form of wear facets, 
microwear scratches and grooves or pitting, the orientation and shape of the 
crowns, etc., as well as the curvature of the jaws themselves. Several of these 
have been investigated, and while jaw biting was primarily assessed by FEA, 
given how iffy muscular reconstruction is, wear pattern and jaw shape pattern 
reconstruction has been much more interesting and "obvious" in its results 
(plus it's less prone to missing information).

  5. I would then argue that the "robusticity" of a tooth is based only on its 
primary axis of bite, and little else: a long, thin tooth will be better at 
"poking" than a large, broad, squat tooth, which will be better at resisting 
bending forces, and was likely used to "rake."

  6. That all said, diplodocids were likely a lot better at brain munching than 
brachiosaurs, able to extract the slurry of goo much better than the others, 
because they'd just more likely open the skull than pulverize it into a messy 
mass. The relevant reduction in sauropod taxa in the northern continents likely 
correlates to the discovery of fire by dinosaurs -- that or chainsaws and 
shotguns.

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: Tue, 19 Jul 2011 07:10:11 +0000
> From: keenir@hotmail.com
> To: qi_leong@hotmail.com; dinosaur@usc.edu
> Subject: RE: Microraptor Wings (and sauropods(
>
>
>
>
>
> > From: qi_leong@hotmail.com
> > To: keenir@hotmail.com; dinosaur@usc.edu
> > Subject: RE: Microraptor Wings
> > Date: Mon, 18 Jul 2011 21:27:54 -0600
> >
> >
> > Perhaps, like some wasps, it used its claws to "probe" certain parts of the 
> > sauropod brain and steered it like the sauropod was a giant zombie bus. 
> > Theropods rule, sauropods (literally!) drool. This zombie-esque quality, 
> > unfortunately, likely resulted in an unhealthy taste for [sauropod] brains, 
> > which explains the relative lack of preserved sauropod skulls. So sad.
>
> Very.
>
> But one question lingers: I thought sauropods only had weak teeth suitable 
> for nipping leaves off trees. Surely the best supporting evidence would be 
> sauropod teeth getting stronger and more durable after the rise of 
> microraptors/protoavians.
>
>
>