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Re: Kickboxing Cassowary



----- Original Message ----- From: "Augusto Haro" <augustoharo@gmail.com>
Sent: Saturday, October 04, 2008 3:32 AM


These features suggest that the jaws & teeth were not used to kill large
prey (*Varanus*, being venomous, cheats). They do, however, suggest that
prey was _eaten_ that was too large to be swallowed whole or ripped to
pieces.

No, small teeth do not suggest killing prey that cannot be swallowed entirely, and large size for teeth indicate possibility of cutting off larger chunks.

_Cutting_ teeth suggest that, regardless of size. Size has other purposes, for example greater bite strength in tyrannosauroids.


There is just an example of a carnivore that can cut
flesh from larger prey with small teeth (Komodo dragon) against many
examples of carnivores that for small relative size of the teeth eat
smaller prey.

And of all those, the Komodo monitor is the only one with serrated, laterally compressed and recurved teeth -- the only one with halfway comparable teeth, in other words.


In addition, the kinematics in the Komodo and the
dromaeos cutting likely differ given the functionally important
flattened snout of the dragon vs. the transversely compressed one of
dromaeos, so that the analogy is not complete.

Sure.

Cats, especially sabertooths, have extremely strong forelimbs for holding
prey in place when the bite is being done (saber teeth were likely too
fragile to be used on struggling prey, and as we're talking about mammals
here, they weren't replaced).

At least for sabertooths, it is not known the true function of the forelimb. I think it has to do with something else than grabbing prey forelimbs robust as those of the lion suffice to hold the flesh of the victim to deliver a bite.

That's not enough for using saber teeth; being more fragile, those require that the prey really doesn't move (in the area between the cat's forelimbs anyway). The most drastic example of a sabertooth cat whose anatomy fits this interpretation is *Xenosmilus*.


If large teeth are to be used against large prey, I suppose yo have to climb upon it.

*Xenosmilus* apparently stood up on its hindlegs for this purpose.

Dromaeosaurid forelimbs are adapted for
maximum speed of movement -- perhaps stabbing movements using the large
finger claws, or holding the prey just long enough for a kick.

But for prey larger than themselves, they should require, unless for ankylosaurs, to jump and hang from the flanks of the taller herbivore. I doubt of these claws stabbing.

Are you sure about this lack? *Achillobator* is named for having a tendon
attachment site on its sickle claws that is as large as the one for the
Achilles tendon in other tetrapods.

All dromaeos have and enlarged ventral process. But these are insertion sites, not origins, where the larger bulk and transverse width of the musculature is commonly located. And the enlarged flexor process might have to do with maintaining leverage for flexors given that when the claws are curved, their basal part is more dorsodistally directed, forcing the flexor tendon to round around the ventral articulation in order to reach the ungual - which can put the tendon to compression, which can result in the formation of sesamoids in other case, which are not seen.

In relative terms, the sickle claws of *Achillobator* are not all that large...


I do think it did that. Why else is the cutting edge [of saber teeth] serrated?

Edges help penetration.

Do _serrated_ edges help penetration?

The lack of sickle claws anywhere outside Deinonychosauria makes all of this
pointless.

No, it doesn't, as the appearence of a novel structure does not indicate the appearence of a new behavior if behaviors more compatible to those indicated by the EPB are consistent with the novel structure.

Except in the case of overdesign.

To admit they cutted
through the limb, you have to counter the argument by Manning et al.
(2006) of the poor performance of the claw against thick portions of
pork meat.

Once again: firstly, this experiment used a replica of _just the bony core_ without any keratin sheath and thus without a cutting edge; secondly, it was unrealistic in having first a straight stabbing motion, then a pause, and then an attempt to drag the claw core through the flesh, rather than having all in one smooth motion.


*Dromaeosaurus* seems to have used the tyrannosaur method: attack by strong
bite. This method is probably more limited by the size of the predator than
generally slashing methods (including the hacksaw method of *Allosaurus*)
are.

If there is a correlation between relative bite force (RBF in future) and sheer size,

That's not what I mean. I mean that prey size _in the particular method of pursuit-and-bite predation_ is limited by predator size (and/or predator pack size), and that any such limit is much more relaxed when generally slashing methods are used.


Jumping height is proportional to leg length (proportional to body length),
proportional to muscle cross-sectional area (proportional to square of body
length), and inversely proportional to body weight (proportional to cube of
body length). All else being equal, it is therefore independent of body
size. Elephants can't jump for the same reason turtles can't jump -- they're
graviportal --, not because they're too large.

Generally in agreement, but with size, the distal limb elements tend to become shorter in digitigrades, including dinos.

That seems to have more to do with elastic similarity than with anything else.


Note that the
animals that jump much have relatively long pes, as frogs, tarsiers,
galagos, some lemurs, small rodents, Ratites, kangaroos, etc.

I said "all else being equal". Of course special adaptations for jumping don't fall under "equal".


A digitigrade of the wight of rhinoceros, however capable of running
better than the elephant, cannot jump, for example.

Sure it can. Just not high enough in comparison to its body size that you'd notice it.


Nor the long-limbed giraffe, as far as I know.

They can gallop (like rhinos), so...

In addition, as you note, the
capacity of exerting force increases with the square of linear
increase in size, while the weight increases with the cube of the
linear increase (much more). Thus, for larger animals, you have
proportionally less force to move your body, and this increases with
size.

At the same time, you have proportionally longer limbs, and this, too, increases with size. This leaves everything equal.


That is the reason by which when taxa increase in size, they
lost some abilities: e.g. lion cannot climb while the similarly built
leopard can,

Incorrect. Leopards are more adapted to living in forests -- and of course trees that can carry the weight of a leopard are more common.


or chimps can brachiate fastly while gorillas apparently not,

Brachiation does have a weight limit -- set by branch diameter. That's not like jumping.


or by which gazellas jump relatively higher than the eland.

Relatively!

In addition, bone resistance increases also with the square of the
linear increase (as it is given by the cross section of the bone).
Thus, for larger animals to maintain a similar morphology, it
indicates bone can tolerate less the shearing forces imposed by the
weight of the individual and its locomotion. That's why at some point,
jumping and running is difficult for large animals. And that's why
large animals tend relatively thicker long bones than smaller animals
of similar body form (e.g., compare Allosaurus with small theropods).

I never said anything against elastic similarity.