Re: Carnivores and Packs

[larrys@zk3.dec.com]

Ralph Chapman <MNHAD002@SIVM.SI.EDU>:
>Perhaps it would be instructive to look at carnivorous birds for
>analogs in the pack vs solitary hunter discussion.

I thought of that - but I don't know of _any_ pack-hunting
birds.  Crows mob and harrass owls and the like, but seem to
hunt alone, and all raptors I could research hunt alone or
in pairs.

tonyf@ucmp1.Berkeley.EDU (Tony Fiorillo):
>       I seem to remember listening to a talk about cooperative hunting
>behavior in one type of North American hawk (it might have been Harris'
>hawk).  The speaker seemed to imply that this behavior wasn't restricted
>to this one type of hawk.

I'd _love_ more info on this...

binder@zk3.dec.com (vitam gustare):
But remember that T. rex was a late Cretaceous character, and - if my
memory serves me - all the big sauropds were long gone by the time he
rolled in.  I think the situation would be more like T. rex facing a
ceratopsian, and it'd be a pretty even battle in terms of size.

Is it really the case the big saurians were gone?  It was my
impression that the number of _species_ had declined greatly,
but that says little about absolute numbers.  Somebody jump
in here.  If that's so, then we have a situation more akin to
tiger-style solitary hunting or to wolf/human style cursorial
hunting.

I recall the debate about 'rexes scavenging versus hunting.  A
cursorial hunter will have enormous physical reserves, able to
maintain the chase for long, long periods of time - that should
lead to obviously different skeletal requirements than simple
scavenging.  If this debate is still serious, then the stalk-
and-pounce solitary hunting seems most likely - but then the
question arises, why lose the claws?  Could even a t-rex do
_that_ much damage to a surprised ceratopsian so quickly without
any means to hold it?  It would have to cripple it before the
critter could turn and get a bead on him with the horns.  And a
forewarned and alerted ceratopsian?  I'd look for lunch somewhere
else, I'm here to tell you.

A cursorial hunter couldn't hunt ceratopsians or rhinoes or other
such things, either.  Cursorial hunters depend on prey that tries
to run away, and tricers don't seem like they'd run - like rhinos,
I'd expect them to face down a predator. Even in this day and age,
nothing hunts rhinos but man, not even lions willing to take on
elephants and cape buffalo. It certainly seems to me that a sol-
itary t-rex would have a very hard time against a triceratops,
even with that large-scale ginsu bite...

I can see a pack of 'rexes hunting a large saurian - or even a
pack hunting a tricer.  I can see an allosaur leaping onto the
back of a tricer from cover and biting into the spine to cripple
it while keeping it from turning around with claws.  But unless
a 'rex could deliver a crippling bite from a pounce attack, and
do enough damage fast enough for it to be reliable _without_ a
means to hold the tricer so it can't turn that armored head and
horns on the attacker, then I _can't_ see a solitary 'rex trying
to make a meal of one.  If a rex were agile enough to use its
_hind_ legs for that, I could see it - but now were talking
about a seven-ton ninja leaping from cover and...well...

Tom Holtz <tholtz@geochange.er.usgs.gov>:
>[Too bad you weren't on the net a few months ago - if someone saved that
>mail thread, you might want to send it to Larrry.]

I thought I was, but I don't recall such a thread.  I'd like to see a
backscroll if anyone has it.  That's "Larry" with _two_ "r"s.  :)

>As much as I like theropods (and tyrannosaurids in particular), none of
>them had enough brains to have been mental giants by today's standards.
>They may have had proportionately larger brains than contemporaneous
>but nothing like the brain of a lion or wolf.

_This_ is a most telling point.  I recall that it was the comparatively
brighter raptors that first triggered pack-hunting speculation, so
perhaps there is some presumed minimal brightness required to support
it.  The thylacine, as you mentioned, would be an _invaluable_ data
point here.  Too bad they're extinct.  :(  (And we know what species
is responsible for it, too).

_Buuuuuut_ - you don't _have_ to have brains to have complex social
interactions.  Witness bees and other social insects.  With a suffic-
iantly large set of pheromones, quite a lot of "pack" behaviour could
be coded into not too much brains, to pick one example that might make
up for the lack.  There might be other ways - not "pack" hunting just
like lions, but "pack" as in "more than one in on it".  Even just a
couple 'rexes hunting more-or-less as individuals but instinctually
picking a common target might be the beginings of pack behavior, and
close enough to at least explain why 'rexes didn't need to grapple
with prey.

>I presume you mean "sauropod".  However, T. rex lived in regions with only
>one known sauropod species (Alamosaurus sanjuanensis), and that wasn't a
>particularly big one.  T. rex is comparable in mass to the most common
>Lancian herbivores, Triceratops (and Diceratops and Torosaurus) and
>Edmontosaurus (and Anatotitan).

Interesting.  Hmmmmmm.  While I can't see loan-rex versus tricer or even
a medium-large sauropod, I guess I can see one versus a "duck-bill".  If
they were the primary prey, then we can imagine a loan t-rex stalking a
herd of edmontosaurusii (God, how I miss "trachodon") and charging into
the herd to grab one at random - that would definitely take advantage of
the bite, which would inflict crippling damage, and, since the prey is
likely dodging, the bite isn't neutralized by a waving tail or a heavily-
armored head.  The 'rex would just grab whatever happened to be handy,
biting and perhaps bearing it to the ground with its feet.  Yes, that
makes sense - but then, what preyed on A. sanjuanensis and the tricers
of the time?

>Actually, the whiplash tails of diplodocids and the club-tails of some
>Asian sauropods might make excellent weapons.

Depends what you mean.  A whip is a nasty defensive weapon, but it
really doesn't do much _damage_ - it just hurts, but in a pinch you
_could_ just charge it.  A club-tail is better, but any tail with
mass could serve as a shield against rear attack.  Which might explain
why they were retained instead of being lost, as they don't seem to
be useful for much else.

>> Big
>>and mean-looking as they are, I'm not so sure a t-rex can move
>>_that_ fast,
>A lot of evidence is suggesting that 10 m/s is well within tyrannosaurid
>speed capablities.  That's better than most of us can do!

That's twenty-some miles per hour, and fast enough for a charge - but
then, most animals can go that fast.  The real question is not so much
raw speed as the agility needed to a) close with the prey, b) position
the jaws for a strike at the backbone, c) strike down at the backbone
while adjusting for the flinch and/or bolt the prey is about to employ,
and d) administer a crippling bite.  That's a pretty spiffy manuever.
Perhaps the part I'm having a hard time with is visualizing the 'rex
- which is no small critter! - as a very agile beast.  And if the bites
_doesn't_ cut the spine, then what?  A tricer will try to spin - that
will either drag the 'rex around by the jaws, or crack a lot of teeth
out, wouldn't it?

BPC.APA@email.apa.org (Considine, Blaise):
>during the Cretaceous, just not quite sure when)? Also, cheetahs and 
>leopards are 2 solitary hunters (virtually all of the time) that I can 

They are both interesting cases, too.  The cheetah is a speed specialist.
It allows the prey to begin running and depends on blazing speed to close
with the prey and attack from the side, presenting opportunities to strike
from at the neck or hamstrings - the jaguar specializes in dropping out of
trees, presenting excellent opportunites for a spinal bite.  These hunting
modes are very specialized, however, and neither seem to fit the 'rex or
allosaur model...God!  That would be one holy heck of a tree!

regards,
Larry Smith