ceratopsians and theropods cont.

["Colette H. Adams" <cadams@hh.gpz.org>]

There have been some excellent responses to my remarks about the hunting
abilities and tactics of large theropods, and responses of their prey.  You
people are terrific; responsive, knowledgeable, thoughtful.  Here are some
follow-up remarks.

1)  Prey animals do not invariably flee every time they see a predator.
They cannot afford to be running like hell every time a predator appears.
In fact, zebras sometimes move TOWARD lions.  Prey animals can often tell
whether predators are actively hunting.  It is quite possible that
ceratopsians could do this.  Thus my statement should be amended to say,
"Triceratops horridus did only one thing when it saw, heard, or smelled an
actively hunting Tyrannosaurus rex...."  I'm surprised no one jumped on me
for that one.  If you noticed it and let it pass, thank you for your
forbearance.

2)  Whether to use the flight option as a first resort is not a function of
the relative speed of predator and prey.  Look at tortoises.  They can
outrun almost nothing, yet they are quite wary and scoot as fast as they
can from any perceived danger.  Of course, it seldom works.  The predator
usually catches them with little difficulty, plays with them for a while,
and gives up.  But they still try to run.  Why?  Because even if it only
works 1% of the time, it will be selected for.  It's always better to avoid
contact if at all possible.  It seldom works, so they have a very effective
backup strategy.  And most predators ignore them.  I suspect the same was
true of ankylosaurs.  They probably tried to scoot as fast as they could
from predators.  And predators probably for the most part ignored them.

3)  The reason I lean toward ceratopsians as an important prey of big
theropods, as opposed to hadrosaurs or something else, is that they seem so
abundant.  This may be an artifact of preservation.  But if not, it is not
reasonable to me that big theropods would pass up an abundant potential
prey just because it has horns.
  
4)  2 to 7 ton theropods were not after baby ceratopsians!  Mothers will
usually defend babies quite vigorously, particularly with herding species.
Why go after the baby if you have to contend with the mother anyway?
Pack-hunting predators often go after babies, but they are typically much
smaller than the animals they hunt.  They work as a team to distract and
occupy the mother while they kill the baby.  A baby ceratopsian is not much
of a meal for a big theropod, certainly not enough to fight with the mother
over.   

5)  Komodo dragons are indeed territorial, and I strongly suspect that
tyrannosaurs also defended territories.  Territoriality will always be
selected for when the benefits of defending a territory outweigh the costs.
 Many, perhaps most, endothermic predators are territorial because their
energy demands are high.  There is a strong advantage to having exclusive
access to an area, and as long as the area is defensible, territoriality
will usually evolve.  This usually means the animal must patrol it with
some regularity.  Again, this selects for cursorial adaptations in
theropods.  Greg has cited studies which seem to suggest that energy
consumption is "about" the same regardless of speed or cursorial
adaptations.  But "about" the same is not good enough.  Even if there is a
0.1% increase in energy efficiency with improved design, it will be
selected for.  Every extra calorie saved is one more that can go to growth,
reproduction, disease resistance, or what have you.

5)  Selection for cursorial adaptations will undoubtedly be of a different
nature in different species.  The selection pressures on kangaroos are
undoubtedly different from those on cheetahs.  The list of factors that
would select for cursorial adapations in big theropods seems rather short.
It may have been sprinting ability for "chase and bite."  But I remain
skeptical.

5)  I realize that large theropods, including Tyrannosaurus rex, occurred
in a variety of habitats, and I do not exclude the possibility of a
tyrannosaur-ceratopsian chase even in forest.  But modern practitioners of
"chase and bite" do not have the weaponry of theropods, and must make
multiple bites on large prey in order to bring it down.  It is difficult
for us to envision how truly dangerous these walking razor blades were,
because big predatory mammals do not have their bladed, serrated teeth.
Those who suggest that tyrannosaurs were not good slashers should perhaps
spend more time with living, breathing animals.  Perhaps they should watch
a big monitor lizard slice clean through the skull of a rat (not the neck,
mind you, the braincase) so fast that the whole process is just a blur.
Perhaps they should observe a 6-foot Philippine crocodile, with its poorly
aligned, poorly bladed, unserrated teeth, nearly cut through a broom with a
quick grab and a few side-to-side yanks.  I reiterate that Tyrannosaurus
rex, with its well-aligned, nicely bladed, serrated teeth and mandibular
adductors more powerful than the largest great white shark, was an
EXCELLENT slasher.  I challenge anyone who doubts it to reconstruct the
jaws and teeth of this animal, put a machine behind them that even roughly
approximates the power of its head, neck, trunk, and legs, set it to work
on a cow carcass, and observe the result.

Thanks for all your responses.

Best regards,

Dave