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Sabertoothed Carnassials in Pandas?



David Marjanovic wrote:

<I only used the lion example to show that carnivores of that size
*can* *in principle* kill elephant-sized prey. And "eleven ton"s for an
elephant sounds like very, very much. Eleven US tons (assuming you mean
these) are nearly 10 tonnes! The highest number for the weight of
full-grown African elephant bulls that I've read so far is 7 tonnes.>

  That's what you get for an off the head estimate. I was using
hyperbole, in any case, trying to emphasize the sheer disproportion in
size.
 
<AFAIK, carnassials are homologous to molars (or premolars -- please
correct me if I'm wrong), and saber-toothed cats did not lose these.>

  True, carnassials are molars. They have three roots. A little
perspective, however, is to be noted: a molar is not a chewing tooth.
The first posterior jaw teeth had _one_ root, then two, on the
longitudinal lengthening of the tooth as it developed much as the
carnassials are used today. This extra root developed to support the
stresses of a large accesory cusp, which incidentally is a good way to
increase how much pressure is asserted in an area, rather than a
specific point. Anyway, the development of the third root is corrolated
with the second accesory cusp, and this is the primitive tooth that the
most basal mammals (Tribosphenida as a whole) walk into town with. This
is good for the interlocking crowns mechanism that one gets with a
lacerating/crushing tooth as insectivores bear, but with a third
accesory cusp. This is the kind of tooth archontans walk _out_ of town
with, and this includes us. Some forms, bats for instance, modify this
form into a more blade-like arrangement [but not carnassial], but this
is apparently secondary in its evolution.

  True chewing teeth like we have is a modification of a simple blade
like form. However, carnivorans and creodonts did not walk down the
same rode out of town: their teeth are not derived transversely, but
longitudinally (mesiodistally), and the labial pair of cusps and mesial
lingual cusp became aligned as a single blade with a talonid basin and
unique shear system. The basal form of this tooth went on in the
subungulates and we get hypsodont (raised, flat-topped crowns with
transverse ridges) teeth for the most part with some basal modified
insectivore teeth in condylarthrans and other basal extinct forms
(horses and elephants are examples of extant forms with hypsodont
teeth, but convergent). Pandas and red pandas modify this to chewing
teeth with low labial cusps and broad crowns; most seals have become
sub-phyllodont, and one seal, the crab-eater, has become truly
phyllodont in all crowns distal to the canines, yet are still
hypercarnivores.

<Okay, this formulation was silly. I meant "only the canines had the
potential to become ziphodont".>

  Postcanines and incisors can become ziphodont, and I would call the
carnivoran incisor sub-ziphodont since it employs a shearing/cutting
mechanism with blade-like mesiodistal edges (not carinae) (and the same
goes for eusauropod teeth -- modified in diplodocimorphs and
somphospondylians[?]). A dog's premolars are also sub-ziphodont, and
may have developed to increase grip when biting [not so sure about this
statement, am researching] by provinding a lowers/uppers interlocking
mechanism mesial to the tearing teeth (other premolars and mesial-most molar).

=====
Jaime A. Headden

  Aaaaaaaaaaaaaaaaaaaahhhhhhhhhhhhhhhhhhr-gen-ti-na
  Where the Wind Comes Sweeping Down the Pampas!!!!

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