Re: Some Speculation (Carnosaur pack hunting)

[Mike Bonham <bonham@jade.ab.ca>]

Larry Smith (larrys@zk3.dec.com) wrote:

> 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.

You forgot the polar bear, a solitary, almost pure carnivore except
for summer when they get to dig a few roots & berries (plus maybe a
few pick-a-nick baskets from the tundra ecologists?!)  They (the bears)
have a very stealthy, patient ambush strategy of searching for seals'
breathing holes & pouncing when the seal comes up for air.

> 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.
> ...
> 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.

Haven't duckbills and ceratopsians been proposed as the most frequent prey
of the tyrannosaurs (i.e. from broken teeth left at the site, teeth marks
on the bones etc.?), rather than the sauropods?  Close to the same
size as a large Albertosaurus or a T. rex.

I wouldn't discount the effect of a 10 meter-long whip under full
muscle power, if it were accurately directed -- might easily have blinded
the attacker, or cut flesh right down to the bone.  And of course there's
Shunosaurus, which added a club to the end for added impact.
The huge mass of a sauropod would make it like an elephant of today
-- which as healthy adults even lions & tigers leave alone.

There are probably many ways to earn a living as a large carnivore.
Pack hunting is certainly one.

Sharks have been suggested as a model for T. rex hunting tactics: slice
a big chunk of meat out of the prey with huge gaping razor-studded
mouth & wait for it to bleed to death.  Or the monitor lizards (komodo
dragons et al) which bite large prey, introducing bacteria from special
pockets in their serrated teeth, and wait for the prey to die of gangrene.
Those strategies would probably work best in a solitary mode.

Regarding potential proof of solitary vs. group behaviour:

> 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.  

The chance discovery of a mass grave site -- a group of animals living
and travelling together caught in a landslide, or flash flood, would
be fairly conclusive.  Sue WAS discovered with other T. rexes, identified
as possibly a family unit.

Another would be a trackway showing multiple individuals travelling
together, or (wonder of wonders) a trackway showing a pack of theropods
chasing a prey animal through, past or or into the mud!  There is a
trackway that seems to show a solitary theropod trailing a group of
sauropods, possibly harrying a single individual (the tracks diverge
in unison at one point).

There may be ways of characterizing the evidence of attack by pack hunters
versus solitary hunters: can one distinguish the bones of antelopes or
wildebeestes killed by hyena (who attack by harrying, nipping and running
the prey to exhaustion) from those killed in solitary attacks, where a
single animal performed a concentrated, single act of ambush, whether or
not the prey was driven toward the ambush by cooperative pack members?
(e.g. leopards (solitary), or lions (cooperative)).

If it could be shown that <insert various smaller theropods> were
regularly feeding on prey that were larger than you could reasonably
expect a single attacker to bring down, it would be evidence of either
group hunting or of solitary or group scavenging.  If you could discount
the scavenging hypothesis (e.g. by somehow proving the prey was fresh-killed
when eaten) then it must be evidence of group hunting.  And if the
smaller predators did it, you'd extrapolate that larger related forms
would be capable of doing it too.

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

Seems like a perfectly fine topic to me, although in the end we may
only be able to conclude there's `insufficient data'.

  Mike Bonham        bonham@jade.ab.ca
``Organization is the enemy of improvisation.'' -- Beaverbrook