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Gangs, packs, etc.



Patrick Norton said:
"I think an important question for this list is how could the
paleontological
record distinguish between cooperative pack hunting, opportunistic
gang
hunting or simple mass scavenging?  How could a paleontologist 70
million
years from now distinguish differences in group behavior between a
fossil
record that preserved a feeding frenzy of sharks from a wolf pack at
a kill?"

Right.  I agree completely with the questions you're posing.  The
problem as I see it (and as others on this list have) is that it is
extremely difficult to understand behavior in fossil animals.  As I am
into "proposing" hypotheses to test, here goes again.

Pack hunting in the mammalian sense is a complex series of behaviors
that not only require mutual team work but learning and adapting to
prey as well.  Part of our problem in this thread is defining what we
mean by pack hunting, true packs, or what have you.  Since most people
think of wolves, lions, etc., when we use pack hunting, and since that
is the context in which many dinosaur pack hunting hypotheses are
created, this is what I mean from now on when I say "pack hunting."

My null hypothesis would be "Pack hunting did not happen in predatory
dinosaurs."  Again, remember my definition of pack hunting is the
mammalian one and does not include gang hunting, opportunistic
feasting, etc.  The alternative of course is that "Pack hunting did
happen in predatory dinosaurs."  We always set these things up so that
our null hypothesis is the default in cases of absence of evidence or
equivalent evidence.  Only when the evidence is definitely in our
favor do we then reject our null hypothesis in favor of the
alternative.

Okay.  Let's talk about relative brain size.  While I'm not trying to
argue predatory dinosaurs were "stupid," "inferior intellectually," or
any other mammal-chauvanism type of thing, we know from endocasts that
most dinosaurs, including many predatory forms, fall in the range of
modern reptiles.  In fact only Troodon (to my knowledge, please
correct if wrong) falls within the bird range of brain size.

With such reptilian-sized brains, I think it is safe to conclude that
the amount of learning and complex behavioral ability needed to form
pack hunting was not present in most predatory dinosaurs.  The
relative brain sizes of most dinosaurs fall no where near the range of
pack hunting mammals, and therefore I would fail to reject our null
hypothesis on these grounds alone.

Furthermore, we bracket dinosaurs by their living relatives, the
crocodilians and the birds.  While crocodilians are complex and
wonderful animals in their own right (as Chris Brochu can attest to),
they are not pack hunting animals.  They do care for their young, they
do have complex behaviors and communications, but they do not form
hunting packs.

Birds, some of which are highly intelligent creatures, also do not
form the sort of hunting packs we see in mammalian carnivores.  Yes,
geese flock together, yes, crows gang up on food or enemies, but no
birds form strictly predatory packs that cooperatively kill large
prey, divide the food based on a hierarchical system of alphas, betas,
etc., and most large raptorial birds hunt alone, in pairs, or perhaps
small groups, and not all the time.  When predatory birds leave the
nest, do they continue to stay with their parents, forming a related
pack?  Or do they set out on their own to find mates and new hunting
grounds?

I think with our bracket, we fail to reject the null on these grounds
as well.

Furthermore, anecdotes about living archosaurs do not constitute
evidence, no matter how compelling, interesting, or neat.  This is not
to say we cannot have speculation on this list, but realize that
that's what it is -- speculation about what dinosaurs might have done
if they behaved like a certain bird, or 'gator, etc.  I'm not innocent
of this myself -- I often find myself watching birds and reptiles and
mammals and wondering if different dinosaurs couldn't have behaved
this way or that.  The problem is (unfortunately!) that none of this
constitutes evidence on which to base a behavioral scenario in dead
dinosaurs. =(

I emphasize that we must be careful about our definitions.  Bees and
wasps cooperate, have complex behaviors, build nests together, divide
labor, are all genetically related, rear offspring, have group
attacks, etc.  Is this herding or pack behavior?  Perhaps in a very
loose way.  But we would never compare bees to mammals and say that
there are bee or wasp packs.  This is admittedly a stretch, but
mammals do not equal dinosaurs, and crows do not form mammal-style
packs.

I hate to say these things, as I am the first to wish predatory
dinosaurs were like wolf packs only scarier (and much cooler looking,
I might add).  For now, the physical evidence from the fossil record
has not convinced the skeptical part of me that predatory dinosaurs
operated normally in complexly structured, mammal-like packs.  But I
am an optimist, and eternally hope that we will find physical evidence
for unequivocal pack behavior in predatory dinosaurs.  Until then, I
see no problem with the lone T. rex or pair of Velociraptors taking
down prey in a less complicated (than mammals) fashion, but in a much
efficient and sexy way, befitting of archosaurs.  Mammals are just too
smart!

My $100.00 worth.

Matt Bonnan
Dept. Biological Sciences
Northern Illinois University