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Dromaeosaur hunting technique (was BCF ET CETERA)



Pete Buchholz Tetanurae@aol.com wrote:
> John Jackson was right in questioning the usefulness of the power-clap in
prey
> grabbing.  The anatomy just doesn't jive with it - the head is in the
way, the
> prey animal would have to be directly in front of it, and the arms aren't
long
> enough to grab anything but the distal tail of said prey animal.

There are surely a variety of possible dromaeosaur hunting scenarios,
depending somewhat on the size, speed, and body type of the prey item in
question, and whether stealth, endurance pursuit, or pack hunting figure
into your view.  In our mammal-dominated world, big cats may finish off
their quarry with a precise bite, but the initial strike is often more a
matter of batting with the paws, snagging or hooking with the claws,
requiring only so much force as is needed to knock a running animal down,
or to drag a standing animal to the ground.  While the claws of
dromaeosaurids bear close comparison with those of cats, the remaining
anatomy is so unique as to defy easy analogies with extant fauna.  Those
weary of reading unprovable hypothetical behavioral scenarios are advised
to skip the following.

Imagine, if you will, a _Deinonychus_ pack leaping onto a _Tenontosaurus_
individual with all claws at once (each theropod pulling its neck back into
an s-curve during the initial strike).  Perhaps the dromaeosaurs would then
quickly jockey for position until each secured a firm grasp of the
ornithopod with their forearms, freeing up the legs to facilitate raking
the ornithopod to ribbons.

Catching a relatively small animal might entail a powerful raking or a
knockdown kick with the powerful feet (think cassowary or kangaroo),
followed by firmly gripping the grounded prey with the hands, and of
course, the obligatory raking with the claws of the feet.

Dromaeosaur arm dynamics, though in some respects more restricted than the
mobile articulations of their mammalian carnivore counterparts, should not
necessarily preclude snagging capability.  Even if a dromaeosaur were to
contact the prey with only one hand, this might be adequate, for the extant
cheetah can knock a running gazelle off balance by hooking it with a dew
claw.  (And the cheetah's dew claws, like the hypothetically raised
dromaeosaur killing claws, are held off the ground at all times, and
maintain their sharp hook, because there is no contact with the ground to
dull them).  Once the prey falls, the theropod could use its arms to hook
into its prey, securing the animal while administering lethal kicks and
bites.

In any case, even if the dromaeosaurid arm anatomy didn't enable rapid
grasping of prey, the articulation would appear to be useful in firmly
holding onto the prey -- "palms"-in --against the force of the kicking
legs.  The semilunate carpals could even enable a dromaeosaur to tuck its
phalanges posteriorly (in the manner of a bird folding its wings) in
_diametric opposition_ to the force of the kicking feet.  With such a wrist
configuration, this swinging of the wrist might occur inevitably (and
fortuitously for the predator in this case).  Were the dromaeosaur to hold
the struggling prey with the hands in the "palms"-forward position, its
kicking feet could actually push the prey animal out of its hands, away
from the predator, facilitating escape!  The "palms"-in articulation is
utilized by small cats holding onto their prey (or their feline rivals)
while raking with the hind claws.  The dromaeosaurid ability to tuck the
hands back against the forearm could represent a further (albeit extreme)
refinement of the technique.

Hence, one could argue that natural selection might favor adaptations which
enable a "clapping" grasp or posteriorly directed hands in dromaeosaurids,
even if such adaptations are not specifically used in "snatching" prey. 
Opponents of this view would argue that the articulations of the shoulder,
arm, and wrist are more plausibly associated with flapping flight, and may
have been present in primitive birds ancestral to the dromaeosaurs.  In
that case, the described hunting scenarios may still have occurred, but the
suggested behaviors would not have provided the driving force behind the
perceived anatomy. 

> Now, instead of grabbing a prey animal, suppose that instead, it was
grabbing
> onto a tree trunk?

I wouldn't rule out that possibility, either, especially with those
jackboots of theirs.  I would have appreciated more thoughtful
consideration of arboreal theropods in the _Scientific American_ article,
but it is not my place to tell others what to think or say.  I provide the
foregoing to suggest some of the many ways in which the dromaeosaur
forelimb anatomy could have possibly been beneficial in subduing prey aside
from the problematical "power-clap in prey grabbing" technique you mention.
 That dromaeosaurs used their forearms in some way is not controversial,
but just how they used them is the question.  In some matters, one can only
speculate, and prepare for the inevitable flames.

Ralph Miller III <gbabcock@best.com>

"It's in the wrist action."