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Re: Kickboxing Cassowary



Aside from the responses below, I think that something indicating that
the dromaeosaurid unguals had not a so specialized slashing function
is that their curvature and relative size are very variable among
dromaeosaurids. Such a variability may indicate different feeding
specializations, but is also compatible with less specific habits,
such as intraspecific combats (as the variable horns of antelopes).
The fact that variability in curvature occurs sometimes within the
same species (Ostrom, 1976) seems to go against specialization. Some
features of the dromaeosaur ungual, as their elevated position, are
not specializations of this type of ungual as are also found in the
smaller clawed troodontids. Thus, there seem to be less
specializations in the claw to be correlated with the presumptive
slashing action, such as the acute ventral border.

David Marjanovic wrote:

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

But the bigger the cutting teeth, the deeper they can sunk into flesh,
and so the cutting border can reach deeper into the larger chunk, to
cut it. As I said before, a simple cutting edge, such as a
ramphotheca, is hardly likely to permit you chopping flesh from
corpses. Both vultures and snapping turtles have an odontoid
projection to help them.

>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.

Damn, you're right in this. But it seems that the Komodo relatively
weak tearing system requires more time for tearing flesh out. This
seems to work better in a more bradymetabolic taxon than in a
tachymetabolic one, as dromeos seem to be. However, this is not
prohibitive.

>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*.

Large prey would likely be stronger than the cat, so they would not be
unmobilized, at most the cat should immobilize itself relative to the
part of the prey to bite. I think the need of immobilizing large prey
it is less necessary the faster the stabbing is accomplished, and the
larger is the ungulate to be chased (the torsos of large ungulates and
paenungulates are realively stiffier than in carnivores and other
mammals, for example).

In any case, to reach the vital areas of large prey, they should jump
or climb and hang on. If not, they should content themselves with
juveniles, what I do not necessarily criticize, but which entails a
problem with your overdesign argument, indicated below.

>>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.

If the prey is small enough, you can. I think Akersten (1985) said
that Smilodon would have attacked juvenile proboscideans instead of
larger ones. But using your overdesign argument, you should need to
hypothesize that they should get prey larger than that, as much
smaller lion teeth are necessary to bring down juvenile proboscideans.

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

Not talking about the size, but about the curvature, I hypothesize the
flexor process is relatively larger the greater the curvature is.

>Do  serrated edges help penetration?

I acknowledge it seems problematic, but if serration helps cutting,
and if cutting helps penetration (as demonstrated by the edged
arrowheads, bayonets and spears and spears, which are
penetration-designed weapons), I would say yes until I hear of some
physical impedement.
Now, I acknowledge the teeth of sabertooths cutted flesh, as they are
mostly comparable to teeth of the Komodo dragon, but if, as you
acknowledge, they are fragile,  then it seems they would not be used
for slashing. The cutting they would be engaged in would have more to
do with closing the mouth, as when tearing flesh from a corpse, and
not have to do with quick slashing.

>Except in the case of overdesign.

Well, I think I said you before that issue of "overdesign" is
theoretically problematic for me.  I mean, I suppose that a mutation
implying a larger weapon, while a smaller variant of the same is
useful for the same task, say, killing juvenile proboscideans, may be
fixed even if the ancestral weapon was also useful, if it permits
greater efficiency in that task (killing the juvenile faster, for
example).  "Overdesign" is not sufficient reason for abandoning EPB
when behavioral correlates of the claw are not sure.

>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.

They did also considered the claw cover in that experiment, or at
least that is what they indicate in the paper (Manning et al., 2006).
They however didn't considered the ventral border was edged, what
should be discussable as it relates to a non-preserved tissue, and the
shape of an ungual sheath has not necessarily to be the same of that
of the ungual phalanx. You are seemingly talking about the TV show
instead of the paper; I did not found reference to that two-phase
movement in paper. In TV shows you have mechanic lion skulls biting
watermelons and lot of fantastic things. Some paleontologists working
on the "Jurassic Fight Club" series have also criticized that they are
not always followed when making the final product.

>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.

Well, first, I do not know of much "slashing ungual-killing"
vertebrate predators in the present as to see the correlation between
size an preferred prey size in that category. Second, as you say,
apparently Domaeosaurus is a dinosaur more comparable to large
tyrannosaurids in teeth size, and probably relative prey size, than
larger carnivores such as Majungasaurus, indicating that size might
not be so related to relative prey-size (almost impossible to test),
or at least feeding mode, in dinosaurs. Indeed, most theropods do not
have strong bites, either large or small.

>>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.

Christiansen (1999) indicates theropod scaling do not fit predictions
of elastic similarity theory. And allometric distal limb scaling that
has to do with that Allosaurus has relatively shorter limbs than
smaller theropods, and thus lesser relative capacity to jump.

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

Jumpers have relatively longer distal parts, so their relative
shortening in large taxa suggest decrease of jumping performance
(that's why they have to do with our Allosaurus example). With respect
to "all else being equal": a) the aspects you indicate are never
maintianed equal with the size increase and b) if they were, the
increase in size would imply animals relatively weaker and more prone
to get breaked legs than when the bones and muscles get relatively
thicker as seen in reality.

>>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...

Never saw giraffes or rhinos jumping, nor read any source indicating
they can. However, its size implies, at least in the rhino, that they
cannot do things other runners can. There is no suspended phase in the
rhino, which is present in smaller  cursors as the horse.

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

I doubt that limb lenght increases relatively with size, I would
rather suppose the contrary. Indeed, if I interpret Christiansen
(1999) right, he says that with size limbs are not so shortened as in
mammals, but does not say that they are actually elongated. Do you
know in what paper was this said?? As the body size is considered by
him as correlated to femoral lenght, and as the distal segments
decrease in relation to the latter, it seems to follow that limb
lenght decrease in relation to body size.

Anyway, Christiansen (2000) indicates that strenght indicator in
theropod long bones decrease with size, indicating not only that their
capacity of fast running is decreased, but also their capacity of
jumping (the part of jumping that more shearing forces on limb bones
creates is while landing). Relative elongation with size would make
the strenght indicator decrease even more, as indicated by
Christiansen.

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

Leopards are opportunistic and also live in the sabana with lions
(they even interact), where they also climb the scattered trees. Now I
can accept that perhaps the shape of the sabana trees imply a fast
change from thick to thin branches, which can be the reason for the
lion not to get higher into the trees. However, lions are ungainy even
in the parts of the trees that can support them, as shown when they
try to steal leopard kills on branches. Tigers are of a similar size
when compared with lions, and live in more forested habitats, with
larger and more capable of supporting their body weight, and yet they
hardly climb.

>Brachiation does have a weight limit -- set by branch diameter.

Ok., trees do not permit to put the experiment to a test, perhaps
gorillas do not brachiate as nimbly as chimps by lack of branches to
resist them. But this does not denies that perhaps in the intrinsic
kinematics of the gorilla there is something impeding that behavior if
sufficiently strong branches were found (as might be the case in large
trees of the western African forest).

>That's not like jumping.

No, but it has to do with the more general point of the decrease in
the capacity of exerting physical prowesses with body size.

>or by which gazellas jump relatively higher than the eland.
>Relatively!

Never saw an eland jumping, but the point holds if accepting that the
gazella can jump relatively higher than the eland. At larger sizes,
bones are relatively weaker if the same proportions are maintained,
and that is why the capacity of exerting physical prowesses decrease.
This does not go only for the non-digitigrade elephants, but for cows,
hippos, rhinos. And can also apply to crocodylians: crocodylians that
gallop are normally the small ones, as far as I know the larger ones
do not gallop.

>I never said anything against elastic similarity.

But I bring this to the discussion to indicate that expecting the
Allosaurus to jump like a smaller coelurosaur would more probably end
with broken bones at landing in the former than in the latter,
indicating why larger animals cannot jump or do the same prowesses of
smaller taxa with similar anatomy (although, as indicated before,
never equal).

Now, perhaps Allosaurus jumped, but in such a case they should jump
very slightly, in any case relatively much less than in smaller
theropods. Or not jumped at all, there is no way to tell, we can only
say that it didn't jumped as small theropods did. In any case, my
point is that size restrict prowesses.

References:

Akersten, W. A. 1985. Canine function in Smilodon (Mammalia; Felidae;
Machairodontinae). Contributions in Science, Natural History Museum of
Los Angeles County 356: 1–22.

Christiansen, P. 1999. Long bone scaling and limb posture in non-avian
theropods: evidence for differential allometry. Journal of Vertebrate
Paleontology 19(4):666-680.

Christiansen, P. 2000. Strength indicator values of theropod long
bones, with comments on limb proportions and cursorial potential. Gaia
15: 241-255.

Manning, P. L., Payne, D., Pennicott, J., Barrett, P. M. and Ennos, R.
A. 2006. Dinosaur killer claws or climbing crampons? Biological
Letters 2: 110-112.

Ostrom, J. H. 1976. On a new specimen of the Lower Cretaceous theropod
dinosaur Deinonychus antirrhopus. Breviora 439: 1-21.