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

Theropod hunting strategies



Tom never seems to keep a copy of the following, but I liked it so
much I made sure I can always find it.  It's been through here at
least twice before, but there are a lot of people who joined after the
last time, and since it seems apropopos I'll resend it again:

  Message-Id: <9411291425.AA20918@geochange.er.usgs.gov>
  Date: Tue, 29 Nov 1994 09:29:28 -0500
  To: DINOSAUR@lepomis.psych.upenn.edu
  From: Tom Holtz <tholtz@geochange.er.usgs.gov>
  Subject: Predation in T. rex and other theropods

    [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.