Some Speculation

[larrys@zk3.dec.com]

I've been doing some research on a background thread on the
habits of modern carnivours, trying to get a feel for the
way dinosaur ecologies may have worked.

We have little or no direct evidence for pack hunting in
carnivorous dinosaurs.  We presume the various raptors
probably were, and I've seen one or two mentions that
allosaurus might have been, but rarely more than that.
I grew up with the t-rex lonely-and-ferocious-hunter
paradigm.

But I can't find too many instances of _non_pack hunters
amongst the living carnivours.  The largest solitary hunter
I can find is a bear, which is an omnivour, and the largest
non-omnivour I can think of is the tiger.  Virtually all the
others are pack hunters to some degree or another.  And even
tigers have a social life, at least intermittantly, and mates
have been known to hunt together.

T-rex doesn't _look_ like he needs help.  He's _huge_, he's
got big teeth, big claws, big muscles - but let's face it,
he's less than a fifth of the size and weight of even a
medium-size saurian.  A modern lion, according to the latest
stuff from Nat'l Geo, can and does routinely hunt animals
that much larger than itself, including elephants and cape
buffalo.  But it needs the pack to do it - as someone once
observed, when a lion jumps on something, it's fighting for
a meal - the meal, however, is fighting for it's life.  The
relative risk factors are important - but lions are willing
to take on quite a lot of risk given the pack to back them
up.

I don't suppose it is likely that dinosaur society was identical
to some modern carnivour, but there must be parallels.  Looking
at the Nat'l Geo article on lions, I suddenly glimpsed a pack
of stalking rexes sneaking through the night, one part harrassing
the saurian herd, another trying to cut one out for a full-scale
attack.  A saurian, mano-a-mano with a 'rex, would have few
defenses except sheer mass - the tails seldom seem to have enough
relative mass or muscle to be real weapons.  Thinking about it,
it seems most likely that a saurian would try to rejoin the herd,
waving that tail back and forth behind it to forestall the 'rex
jumping it from behind.  The 'rex, meanwhile, would be trying
for a neck or spinal bite to incapacitate the target - very, very
difficult to do in a stern chase.  If the 'rex was a solitary
hunter, it must've been far more stealthy and sneaky than Spiel-
berg ever imagined, and it would have had to be either blindingly
fast, to forestall the target from turning away, or capable of
inflicting lethal damage on a saurian in very short order.  Big
and mean-looking as they are, I'm not so sure a t-rex can move
_that_ fast, nor dish out damage _that_ quickly to something much
larger than itself.  It also seems to me that such a hunter would
have needed arms to help latch onto and hold the prey, so as to
increase the "dwell" time and thus increase the probability of
inflicting a lethal bite.  This seems more plausible for an allo-
saur, and better for smaller prey - and the tiger, even though
bigger than most lions, does specialize in prey not much larger
than itself, and usually much smaller.  As do wolves hunting
alone.

_But_ - if the 'rex was backed up with a pack, then the retreating
saurian would be in a world of trouble as other members of the
pack bored in from the side or headed it off.  A saurian surrounded
by 'rexes would be a goner, but still a dangerous adversary because
of the mass and because, if panicked (and I surely would be if I
were surrounded by a hunting pack of t-rexes) it might lunge
through and break the line, possibly trampling one or more of the
rexes (possibly breaking a leg?).  The same thing can seen today
with lions hunting elephants and cape buffalo.  It is now less
important to physically grapple the prey - just head it off and
keep it from turning away from the bites.  Interestingly, wolves
show much the same behavior when pack hunting - they use no claw
attacks at all, just the bite, and they, too, tackle very large
prey, relatively speaking.  Similarly the hyena.

Social activities are the hardest thing to get from fossils, but
we can get some clues if we find enough sites (and I have no idea
if we have).  Sue showed signs of a broken leg that had healed -
this tells us two things: not only that she was majorly hurt some-
how, but that she was able to survive while it healed.  I doubt
she could hunt with a busted leg, but she could probably keep up
with the pack - the pack covers a lot of ground hunting, but, like
lions and wolves, might range out from just a few base areas.  She
could hobble to the kill and hobble back while the leg healed.

This sort of turns the usual portrayals of 'rex and allosaurus on
their heads, but it seems more consistant with actual hunting
patterns we can see today. Injuries amongst lions hunting elephants
and cape buffalo are very common - injuries to bears and tigers,
more prone to hunting smaller prey and with no need of a pack
structure to back them up, seem to be relatively rare, they usually
die from starvation, disease, or other mishap besides physical
injury.  In other and simpler words: pack hunting seems to arise
where the risk to the predator for each meal is much higher than
it is for non-pack hunters.  Greater numbers spread the risk.

So, if these speculations are close to the mark at all, then pack
hunting predators we find would have injuries - recent, perhaps
the cause of death, like the first deinonychus whose claws were
still imbedded in a protoceratops, if I recall correctly, or
healed or partially healed, like Sue.  Killed while hunting would
be the normal way for a predator pack dinosaur to check out.  These
two examples happen to be the only sites I have heard about in
enough detail to know if they support this view or not, and both of
them seem to.  Are there others?  Is such collateral damage "normal"
in certain predatory dinosaur finds?  And, more importantly for
testability, is such collateral damage _not_ the norm in certain
other species, such as allosaurus?  It would be very instructive
if most t-rex skeletons show damage and most allosaurs do not, for
example.  Of course, we might lack enough skeletons to decide either
way.

'Course, I might be completely off any reasonable beam.  Let me
know if these kinds of speculations are _not_ welcome here.

regards,
Larry Smith