Predation in T. rex and other theropods

[Tom Holtz <tholtz@geochange.er.usgs.gov>]

[I tried to stay out of this as long as I could.  I really did... ;-)]

Since I have done some degree of research in this field, I thought I ought
to state my conclusions/opinions on the subject of Tyrannosaurus predation:

Among large modern terrestrial hypercarnivores (a useful term mammalogists
use for animals which derive >95% of their food in the form of vertebrate
flesh), there are three major predatory repetoires:

1) Grapple-and-slash.  Best typified by modern felids (cats), these are
predators characterized by highly compressed, recurved, blade-like claws on
the hands and feet; relatively short and powerful limbs; and tails used as
dynamic stabilizers to allow for quick turns.  Grapple-and-slash predators
are for the most part ambush predators, which seize the prey with the
forelimbs after a very short chase.  The prey is then dispatched with a
combination of slashes from the forelimb, disemboweling kicks with the
hindlimb, and bites and/or suffocation with the mouth.  Grapple and slash
predators are not particularly fast in the long run, but are good for short
acceleration.  [And for some reason, Jack Horner seems to think that this
is the preferred form of predation, despite it being limited today to only
one major group, the Felidae].

2) Grapple-and-bite.  Best typified by modern raptorial birds, these are
predators characterized by claws which are curved but fairly round in
cross-section.  These claws are at the end of fairly powerful limbs.
Grapple-and-bite predators today are for the most part ambushers ("death
from above"), which seize the prey with the forelimbs, dispatching the prey
with bites to the neck or back, and flying away with the carcass to eat
elsewhere.  The claws are used primarily for holding prey, while the jaws
are the main killing tool.

3) Pursuit-and-bite.  Typified today by canids (dogs, wolves, etc.),
hyaenids, the cheetah, and in the recent past by flightless predatory
birds.  The claws of pursuit-and-bite predators are for the most part not
highly curved and are rounded in cross-section.  These predators do have
powerful jaws and necks, long teeth, and relatively long limbs.
Pursuit-and-bite predators characteristically run down their prey after a
fairly long chase, seize the prey in their jaws, and kill the prey with a
combination of biting and suffocation.  The claws, if used at all, are used
to stabilize the victim so the jaws can do their work.

Comparing theropods to these repetoires, it is fairly easy to relate
different groups to the three catagories.  Dromaeosaurids are excellent
candidates for grapple-and-slash predators, since they proportionately
short and stout legs (forget ever reference you've seen to Velociraptor and
Deinonychus as being "swift" as dinosaurs go.  Even Tyrannosaurus rex has
proportionately longer lower legs and feet than do these smaller forms).
The claws of the hand and the sickle-claw of the foot match the proportions
and angle of felid claws very nicely, and the tail of dromaeosaurids has
been known to be a dynamic stabilizer since 1969.  And of course, the
fighting Velociraptor specimen is in classic grapple-and-slash predatory
attack, inculding the disemboweling kicks to the belly of the
Protoceratops.

Most large theropods (allosauroids, megalosauroids, Dryptosaurus, etc.),
match some variation on the grapple-and-bite theme.  The hand claws of
these animals closely match the proportions and angles of predatory birds,
and are at the end of short but powerful arms.  Like predatory birds, these
claws were probably not the primary weapons of killing, but were used to
seize and hold the prey while the jaws did the work.  Note that it is these
animals, and not dromaeosaurids, which match modern "raptors" the best.

Tyrannosaurids fit well with the pursuit-and-bite catagory.  Like canids
and hyaenids, they have proportionately long legs (T. rex itself has legs
which are more "cursorial" than the man-sized herbivore Dryosaurus and
other accepted runners), very powerful jaws, and claws of the hand and feet
which are not highly curved and rounded in cross-section.  Although they
may not have pursued prey for wolf-like distances, the body of anatomical
evidence points to the adaptations of tyrannosaurids as being predatory,
and specifically pursuit-and-bite predatory, features.

And as for scavenging - none of the alledged scavenging features suggested
by Horner holds up in quantitative or comparative analysis.  His claim that
predators need to use their forelimbs in prey acquisition does not stand
the test of observations of the modern world.  Tyrannosaurids show more
cursorial adaptations than any other large Late Cretaceous Asiamerican
dinosaur (hadrosaurids, ceratopsids, ankylosaurids, etc.), so they probably
were faster than any of these.

BUT...  as others have already pointed out, scavenging and predation are
not mutually exculsive behaviors.  In some regions of Africa, for example,
lions are predominantly scavengers and hyaenas the major predators, while
in other parts of the same continent, these roles are reversed.
Tyrannosaurids would be in a good position to bully any other theropod away
from a corpse (dromaeosaurids arguably may be more deadly pound for pound,
but tyrannosaurids had a LOT more pounds...).  It is not unreasonable that
certain individual tyrannosaurid populations, or even species, may have
gotten most of their food from carcasses.  Nevertheless, the anatomy of
tyrannosaurids indicates that they were capable of dispatching prey using
techiniques grossly similar to those used by canids, hyaenids, and the like
- running down animals, seizing them in their jaws, and ripping out huge
chunks and/or suffocating the prey item until it was dead.

Thanks for your time,

                                
Thomas R. Holtz, Jr.                                   
tholtz@geochange.er.usgs.gov
Vertebrate Paleontologist in Exile                  Phone:      703-648-5280
U.S. Geological Survey                                FAX:      703-648-5420
Branch of Paleontology & Stratigraphy
MS 970 National Center
Reston, VA  22092
U.S.A.