[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Dinosaur Hunting Techniques



This is a repost of sorts; I posted this the first time on the
Sci.bio.paleontology newsgroup, but I think it is rather appropriate for this
area as well.  My apologies to anyone who's already seen it.
******
Back when I was an undergrad at UCB, I wrote a paper for a Functional
Morphology course in which I discussed the correlation between skeletal
morphology and hunting techniques of two modern predators:  the African
lion, and the cheetah.  My intent, however, was to eventually be able to
use this kind of thinking to examine the hunting behavior of extinct
animals such as dinosaurs.  From what I have read, little (if anything)
has been done in this area with respect to therapods.  We know they
hunted.  Sometimes, we even know what they hunted.  But, we don't know HOW
they hunted. 
Take for example the lion and cheetah.  Both are big cats, of course. 
Both share roughly the same habitat.  Both even share some of the same
prey (both prey upon Thomson's (sp?) Gazelle, for example).  However,
since they are built differently, they hunt differently.  The lion's top
speed is about half that of the gazelle, whereas the cheetah can match or
exceed at least a young gazelle in speed.  Obviously, then, it just won't
do for a lion to try the "run 'em down" approach.  Lions, as it turns out,
are accelerators.  With their powerful hind limbs, they have a higher
acceleration than does any of their prey.  Obviously, this means that the
lion specializes in short chases, using stealth to approach very close to
its prey before attacking.  In this way, it can often catch a gazelle long
before the gazelle has a chance to reach its top speed (at which point a
lion has absolutely no chance of success).
The cheetah, on the other hand, usually needs only to start its attack run
BEFORE its prey starts running.  It then uses its superb speed to simply
overtake its prey and drag it down with its "dew" claw.  Of course, the
closer it can get, the less running the cheetah will have to do, so it
relies on stealth to get closer, but not quite to the degree that the lion
does.  Another observation is that both lion and cheetah tend to trot
around while hunting, thereby giving them a slight head-start speed-wise
when the chase starts (most prey start from a standstill).
Now....What makes the lion an effective accelerator is the way the muscles
attach to the limbs.  Simply put, the tendons attach far down the limb
bones, allowing for a large amount of torque when the muscle is
contracted.  The cheetah's tendons attach closer to the joints.
What is needed, then, is to carefully examine the tendon-scars on, say,
the tibia of a given therapod.  The more distal the scar from the
knee-joint, the more likely the animal is to have hunted similar to a lion
(of course, to gain a complete picture, the same sort of analysis would
have to be done on any possible prey).  Of course, tibia scars alone will
not be sufficient to extrapolate an entire behavioral pattern such as
this.  The whole animal needs to be considered.  Is it built for the
stress of a high-speed chase?  Does it have more adaptations relating to
speed, or does it look more like a jack-of-all-trades, so to speak. 
Cheetahs are highly specialized for running.  They have lost many of the
typical "cat" features, such as protractile claws, large canine teeth,
etc.  Consider the tyrannosaurs.  These animals seem to have concentrated
on two main areas: the head and the hindlimbs.  The forelimbs are, as
everybody knows, much reduced.  Suppose, then that tyrannosaurs took the
"high speed" route.  They developed the standard suite of cursorial
adaptations (long limbs, digitigrade stance, etc.), then took it even
further to reduce weight and drag by reducing the forearms, then (or
rather, simultaneously) increasing the power of the neck and jaw so that
those elements would take over the function of the forelimbs in bringing
down prey.  That they didn't go all they way to unguligrade stance may
have to do with the fact they were bipedal, and having only two toes
support such an animal was simply out of the question, evolutionarily
speaking.  And, if one thinks that the reduction of the forearms as an
adaptation for speed is silly, consider this:  the cheetah has greatly
reduced canine teeth, as compared to other "big cats".  Why?  The roots of
long canine teeth extend up through the maxilla and part of the nasal
bone, thereby blocking off part of the nasal cavity.  By reducing the size
of the canines, and subsequently the roots which hold them in place,
cheetahs have essentially expanded their nasal cavities to provide for
more efficient respiration during a chase.  I realize, of course, that
reduction of the forelimbs is not going to directly affect respiration. 
However, suppose that by reducing the forelimbs, and subsequently the
shoulder girdle, the ribcage is somewhat less constrained (the shoulder
girdle of reptiles and birds is much more rigid, remember, than it is in
mammals), so that perhaps a deeper breath can be taken.  This would allow
the tyrannosaur to take in oxygen a bit more efficiently than it might
otherwise be able to.  Whether or not this is the case, or even if such a
change would produce a significant change in oxygen intake, I do not know.
But it seems a plausible idea.
By examining the skeletal remains of therapods, it seems possible, then,
to determine at least qualitatively how they might have hunted.  Of
course, to gain a complete understanding, we would have to examine the
potential prey animals as well.  If the average hadrosaur were also built
for speed, then perhaps tyrannosaurs learned to stalk.  Or maybe
hadrosaurs just stood their ground (granted, this is not usually the rule
among herbivores - most, being somewhat less intelligent then the
predators, will simply bolt and run when attacked.  However, dinosaurs
seem to have broken many "rules").  This would also affect the hunting
technique of the predator.
It is my belief that this sort of analysis, performed much more in depth,
and based upon the actual bones, rather than the above speculation, will
provide us not only with a more complete picture of individual dinosaur
species, but will enhance our understanding of dinosaurian ecology as
well.
As a slight aside, it is curious to note that, as in the case of the
cheetah, most analyses of animal locomotion concentrate on limb movement
patterns and speed.  Very rarely, if at all, are such factors as the
acceleration abilities considered.  Cheetahs are known to be good high
speed runners.  But no one really knows how quickly they can reach those
speeds, because that sort of research has just not been done.  Our current
understanding of the acceleration abilities of animals is poor, but I
believe that these analyses are important to gain a proper understanding
of behavior patterns such as those needed for hunting or escape.  

Thanks for reading.

Derek Smith