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Parts & Non-Recreation (was RE: dino-lice)



Sorry about the lateness of this reply. I get a day off on occasion; that is 
usually when I start making time to work through my various backlogs.

Anthony Docimo wrote:

<[The] teeth of sauropods kept getting simper and more basic, even while the 
rest of the body got bigger and bigger to eat more?>

Jason Brougham wrote:

<I said extreme reduction, meaning in size, from the ancestral state. I 
don't think sauropod feet are so much smaller than prosauropod feet. No,
 I don't mean like that, as I don't think anyone has suggested a 
locomotory function for alvarezsaur arms. I don't think any sauropods 
are edentulous, but some animals of course are, and this indicates that 
their teeth stopped being important in feeding.>

  It's one thing to argue that a reduction in any dimension from the ancestral 
state is a trend toward vestigialization, where this dimensional trend is 
reflective of a lack of functionality, or its progressive loss. Such an 
argument can be useful when we have a substantive amount o0f ecological data 
that allows us to conclude that the anatomical region in question is not 
undergoing selective pressure. It's another thing to argue that an essentially 
"reduced" region of the body has "stopped being important." Without context, 
such a statement is useless for projection of any hypothesis. It's a 
non-hypothesis. The statement above doesn't help matters, as the conclusion -- 
what follows "indicates" -- does not follow from the precedent.

  Whitlock's recent work is to propose a functional case for the use of teeth 
in all sauropod grades, attempting to find out what, if anything, sauropod 
teeth may have been useful for. This is coincident with work on the shape of 
the jaw. Previous work has used the shape of the quadrate-articular joint, the 
mere length of neck, the environment of fossil recovery, or even size to infer 
diet or lack thereof. In doing this, Whitlock must assume the teeth were doing 
something (otherwise they would not be there, so the hypothesis might go).

  Of course, the above statement was not specifically about sauropods losing 
any teeth, but it is important to note that that not all animals with teeth 
even use them for feeding (or if they do, not on their particular favored 
foodstuff) while at the same time several animals feed on the same foodstuffs 
but show vastly different jaw apparatus and conditions of development of teeth 
(including their lack). Some animals compartmentalize their dentition, with 
certain teeth having a potentially non-dietary function (colugos may represent 
this trend, where mesial dentition is particularly odd and divergent from any 
other type of incisiform in any vertebrate known).

http://www.boneclones.com/images/bc-049-lg.jpg

Beautiful.

  Sauropod dentition is "reduced" in a few senses: 1, in form -- from the 
complex structure, from the "eusauropod" condition (i.e., *Brachiosaurus 
brancai*): "spoon-shaped," V-shaped facets along the crown margins, with 
marginal denticulations in unworn crowns; 2, in number -- where the n is 
decreased in absolute value; and 3, in aspect -- the extent of the jaw margin 
along which denition exists. Sauropods with "reduced" dentition include 
titanosauroids (e.g., *Nemegtosaurus mongoliensis*), rebbachisaurids (e.g., 
*Nigersaurus taqueti*), and diplodocids (e.g., *Diplodocus longus* -- we can 
pretend this is *carnegii* and *hallorum,* as well), and several for different 
reasons.

  With rostralization (#3) of dentition, "reduction" is not necessarily 
occurring because what is actually happening is that the dentition is being 
restricted to a broader mesial portion of the jaw, along with shape alteration 
(#1) of the teeth themselves, allowing the same number -- or even more of them, 
an inversion of #2 -- to be packed into the area.

  When comparing to alvarezsaur limbs, we argue that the limbs are "reduced." 
In overall size or aspect (#3) this is true, when compared to other landmark 
bones (femur length, overall body length, trunk length, etc.); in form (#1) 
this isn't actually true, and the manus is particularly large compared to the 
non-manus portion of the limb, in particular comparable to many paravians and 
avialaians[?]. While loss of the external digits occurs, the first digit has 
been modified in form from a typical cylindrical phalanx and mediolaterally 
compressed ungual into a broad, "flattened" phalanx with [distinctly] developed 
[asymmetrical] ventral process and broader ungual with reduced flexor tubercle, 
features that are highly unusual even when animals with "reduced" limbs are 
concerned. My assumption is that this was progressive, with development of the 
manus prior to limb size reduction, which seems to coincide with body size 
reduction. This corresponds with phylogeny. Why? I have no clue.

  Tim and Jason had an interesting exchange talking about what the "reduced" 
limbs of alvarezsaurs might mean, but I would argue that regardless of 
reduction of the limb _size_, comparably "reduced" limbs in other animals (the 
kiwi has been brought up) lack the robusticity of the bones of alvarezsaurs. 
Jason mentions stout-limbed dachshunds, which have bowed diaphyses and robust 
epiphyses; Jason shows other animals (and humans) with various limb 
deformities, but there is an issue involved: dachshunds and bulldogs are the 
product of bred deformity, most significantly chondrodysplasia, which is 
congenital and abnormal for developing dog fetuses. We have this information 
because we have the critical context we need to use it. To use an old analogy, 
aliens coming to the earth may not have this information, can look at the 
morphology of dogs found as fossils, or genetics from subfossils, and use this 
information to infer a collective species concept distinguishing these 
organisms wholly; but we'd know they'd be wrong, due to the critical context of 
lacking the developmental issues involved. Dachshunds are the product of a 
genetic breeding program selecting for a sometimes-critical disease. I cannot 
find any contextual reason why you'd want a maloccluded bulldog other than some 
sense of its appearance, or the nearly nonexistent nasal sinuses in various 
breeds, also in some cat breeds. We humans can be horrible at pretending 
breeding equals evolution, and this shows in many, many ways.

  Alvarezsaur limbs show little to any case for deformity other than the 
relative restriction in movement at several joints, while a case is made that 
compares (positively) for this restriction in other taxa which employ this 
movement in a particular fashion (digging). Not only do the limb bones lack 
irregular torsion or curvature, every single specimen of alvarezsaur, from 
several continents, exhibit the same or similar morphology (*Haplocheirus 
sollers* is the only exception). The only problem that I think is present, and 
the one that dominates this discussion, is one of size, and this seems 
incomparable to the issue of deformation above. This is primarily due to the 
length of the neck and to the length of the limbs, which point habits for the 
animal in different directions. I have NO idea why we should be trying to 
constrain limb functionality in the fore to the hind in a bipedal animal, and 
this puzzles me in the discussion involved.

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)