RE: Parts & Non-Recreation (was: Ceratonykus)

[Jaime Headden <qi_leong@hotmail.com>]

Tim Williams wrote:

<I took "myrmecophagous carnivores" to mean "myrmecophagous Carnivora". If the 
latter, I know only of two: the aardwolf (_Proteles cristatus_) and the sloth 
bear (_Ursus ursinus)_. However, I don't think the sloth bear really qualifies 
as myrmecophagous; it's more of an omnivore. In any case, among ursids its 
termite-eating habits appear to be extremely recently acquired.>

  I actually meant that the animals involved were "meat-eaters." Their 
generalist diets will often include one form of vertebrate or another, and when 
insectivores can also be "flesh-eaters" ("vermiphages" or "worm-eaters" employ 
jaw and dental adaptations akin to vertebrate meat-eaters, modified only by the 
scale of the apparatus involved), it blurs the line between "insectivore" and 
"carnivore," so I meant "carnivore" in the ecological, rather than 
phylogenetic, sense.

<There really are no hard-and-fast rules regarding the craniodental adaptations 
of myrmecophagous mammals - either than there being a trend to simplify the 
dentition (sometimes culminating in outright loss), and narrowing and 
lengthening of the rostrum.>

  I have previously cited work that refers to craniodental adaptations to 
myrmecophagy, but as these details were restricted to squamates which, by their 
rules, have elongated but "broad" snouts (generally due to the anterior 
position of the orbit to length of the skull), it's a little loose. The 
craniodental adaptations I would use to categorize myrmecophages, if I could so 
do, would be similar to those I would identify to durophages, and the reasons 
are similar, and even match as scale changes.

  A durophage is a consumer which requires the mandible, cranium and palatal 
system, hyolingual apparatus and musculature to operate in such a way as food 
is processed intraorally. At small scales, this is employed almost exclusively 
by the hyolingual apparatus against the palate, while at large scales teeth are 
generally used. Mammalian insectivores will tend to lose teeth rather than 
employ them to feed, largely because the relative proportion of food to jaw 
size is so extreme. Durophages show a trend toward reduction of teeth from an 
ancestral state, such as *Globidens* compared to *Progranthodon* or *Moloch* 
versus *Agama*. In typical carnivorous teeth, the jaws form a strongly serrated 
or nearly continuous shearing edge (as in *Sphenodon*) while in durophages the 
dentition is more clearly punctated (clear gaps or pauses between the apices of 
teeth beyond the distance for another tooth from the opposing jaw).

  Teeth in durophages occur in two forms: small, pointy and sparse, or large, 
oblate and blunt (they may also be sparse). Comparisons include *Cyamodus*, 
*Globidens* and *Pycnodus*.

  The palate is always expanded posteriorly, and almost always a secondary 
palate is formed where the maxillae meet the vomer or pterygoid at the midline, 
or are themselves extremely broad. Intracranial joints are diminished in 
flexibility, if not completely lost, due to requirements to transmit loading 
forces into, rather than away from the jaw edge. The hyoids and the hyolingual 
musculature, including medial mandibular attachment sites, are well-developed, 
with higher circumference and greater length and often greater curvature of the 
ceratohyals (hyoid "horns") being one of the primary indicators, but also a 
well-developed basihyal -- this is regardless of the protrusiveness of a tongue 
(if it has one) or not.

  Insectivores show durophagous adaptations, which of course means they are 
durophages. Depending on the diet and relative size of food, an insectivore 
uses one of two methods to consume insect prey: 

  1. Relatively large prey must be masticated (or swallowed whole), requiring 
an oral processing system, and thus developed teeth or robust 
hyolingual/palatal system; these teeth are generaly very high cusped with 
developed talonids (in mammals) and a "mortar-pestle" crushing system where the 
tooth takes the job of the whole palatal system (see *Zalambdolestes* and 
*Solenodon*).

  2. Relatively small prey do not require teeth, and thus hyolingual/palatal 
crushing is the primary, rather than secondary, method of processing.

  There's a lot to say on this. It's a lot more complicated than, say, to argue 
that a single feature is a good indicator of diet, but it in conjunction with a 
few other features does appear a good indicator. It suggests to me, for 
example, that anurognathids are indeed durophages specializing on insects; 
their wing shape and general flexibility in flight appears to support this, in 
comparison to bats and birds that primarily prey on insects ... in the air. It 
also suggests to me that alvarezsaurids were vertebrate specialists, like 
troodontids, not insectivorous durophages. At least, that's the "neat" answer, 
and is horribly preliminary. Note something that hasn't been brought up: why 
did alvarezsaurs use their arms for digging, when they have perfectly good legs 
that other avian diggers use instead (wing-shoveling loose soil or snow, but 
foot-based digging)? Like Tim, I'm tending to think that alvarezsaurs are not 
even "close" to an anteater analogue, but I'm not prepared to add "insectivory" 
into this at all.

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: Sun, 1 May 2011 17:03:25 +1000
> From: tijawi@gmail.com
> To: dinosaur@usc.edu
> Subject: Re: Parts & Non-Recreation (was: Ceratonykus)
>
> Jaime Headden  wrote:
>
> >  Virtually all myrmecophagous carnivores use non-dental processing to deal 
> > with termites and ants, which would necessarily seem to invoke the 
> > "vestigialization" argument for them with regards to their
> > teeth ... yet despite this, they have teeth and a lot of them. Like 
> > troodontids, this dentition is arrayed into a blade-like jaw margin.
>
>
> I took "myrmecophagous carnivores" to mean "myrmecophagous Carnivora".
> If the latter, I know only of two: the aardwolf (_Proteles
> cristatus_) and the sloth bear (_Ursus ursinus)_. However, I don't
> think the sloth bear really qualifies as myrmecophagous; it's more of
> an omnivore. In any case, among ursids its termite-eating habits
> appear to be extremely recently acquired.
>
>
> Among extant mammals, there is a sliding scale as to how the jaws and
> teeth have been specialized for myrmecophagy. Echidnas, anteaters
> (vermilinguans), and pangolins have all lost their teeth, and the
> mandibles are fairly shallow and delicate. Others retain teeth
> (numbat, aardvark, aardwolf, some armadillos), but tend to have small
> homodont teeth housed in a long and tubular skull. Of the latter,
> some have reduced the number of teeth, others show a slight increase.
> The aardwolf retains large canines. Elephant-shrews have large
> canines, and hypsodont cheek teeth.
>
>
> There really are no hard-and-fast rules regarding the craniodental
> adaptations of myrmecophagous mammals - either than there being a
> trend to simplify the dentition (sometimes culminating in outright
> loss), and narrowing and lengthening of the rostrum. In that context,
> I'm prepared to go along with alvarezsaur jaws and teeth being adapted
> for omnivory or insectivory, with termites making up a component of
> the diet. But I would not call any alvarezsaur a "dinosaur anteater".
>
>
>
>
> Cheers
>
> Tim