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Re: Dromeosaurid behavior........Pack hunting!



Hey Truett:

I responded to MegaRaptor when he sent his email on this topic to the
vert paleo e-mail list, but since I wasn't a member of this dino list
until recently, my reply didn't get printed over on your side.  Here
were my two responses to MegaRaptor.  I hope MegaRaptor doesn't mind
me reprinting these, but I think they might help you out.  I'll warn
you -- this is a long e-mail, but I really hope it helps out.

Sincerely,
Matt Bonnan
Dept. Biological Sciences
Northern Illinois University

1st e-mail:
MegaRaptor:

It sounds like you really like dromaeosaurids, especially Deinonychus
(who wouldn't?), and I think you've convinced yourself that pack
behavior in these animals is inevitable.  I am a graduate student now
working on my Ph.D.  You've probably been interested in dinosaurs for
a while (I'm guessing) and I know when I was 17 (I'm 26 now) it seemed
that a lot of the scientific community were way to conservative and
hardnosed when it came to interpreting dinosaur behavior.

First of all, it's good to see you've put some thought into this, but
it's hard to really know what is going on with specimens unless you
actually see them in three dimensions, or visit certain dinosaur
localities, etc.  I'm not suggesting you haven't done this, but my
guess would be that most of your exposure to dinosaur data has been in
museum displays and perhaps you've participated as a volunteer on
dig?

Let me tell you, from my own experience with sauropod dinosaurs, that
you can look at hundreds of photographs and illustrations and still
not really understand what is going on with a fossil animal until you
actually hold the thing in your own hands, turn it around, look at it
from various angles, measure it, etc.

And of course, these animals, no matter how alive they are in your
head, are very much dead.  We only have a very narrow amount of
information available to us, because these animals first had to die,
their carcasses had to "survive" scavenging, their remains had to be
buried fast (and only in certain sediments at that), the remains have
to fossilized, the remains can become distorted, then they erode out,
someone has to catch them at the right moment, not all the bones are
collected, their remains are brought to a collection, they're
prepared, and then finally a paleontologist can begin to really look
at the bones and describe them!

So, with that in mind, there are more things to consider.  We cannot
(although wouldn't it be awesome if we could?) observe living
dinosaurs doing their things.  We have to collect extremely indirect
evidence, and in most cases it is equivocal -- not supporting or
rejecting our hypotheses.  But let's examine your hypothesis ...

When we come up with a hypothesis in science, we try to phrase so
that we are likely to REJECT it.  Once you have an idea you really
like (I know I have a few about dinosaurs myself), it is very easy to
find evidence to confirm, at least to yourself, that you're right. 
But we want to try to get rid of our own personal biases as much as we
can.  Otherwise, we might overlook or subconsciously ignore
contradictory or vague evidence.

So, we could start out setting up a hypothesis like this:
Dromaeosaurids did not hunt in packs to bring down big prey like
Tenontosaurus.  We would call this your null hypothesis.  Then we set
up a different, or alternative, hypothesis like this: Dromaeosaurids
did hunt in packs to bring down big prey like Tenontosaurus.  In every
case where the evidence is equivocal or vague, we fall back on the
NULL hypothesis.

Let's look then at the Tenontosaurus situation.

Evidence 1: Deinonychus and Tenontosaurus are both known from the
Cloverly Formation.  Of course, just because two animals are found in
the same locality doesn't mean that they interacted with each
significantly.  We fail to reject our null hypothesis here.

Evidence 2: There are teeth of Deinonychus present with Tenontosaurus
remains at more than 16 sites in the Cloverly.  Okay, we have teeth
associated with this big herbivore.  But here are some things to
consider.  The teeth may have been shed during an attack, but there is
no evidence at any of these sites to outright reject the possibility
that these Dromaeosaurids were just being opportunistic scavengers. 
The teeth could just as easily be shed by scavenging theropods as well
as actively predating ones. Hmmm ... looks like we can't be sure
again, so we fall back on our null hypothesis again.

Evidence 3: Some specimens of Tenontosaurus appear to have bite marks
in the bones and are also associated with Deinonychus teeth.  Great! 
Irrefutable evidence, right!  But, wait!  Who made the bites?  How do
we know that another dinosaur, or even something like an alligator,
didn't make the bites?  We don't.  It's really tough to match up teeth
marks with dinosaur jaws, because teeth can slip, or not penetrate in
certain areas, or any other number of problems.  And even if we were
to show that indeed Deinonychus or another dromaeosaurid bit the
Tenontosaurus, it wouldn't tell us whether the bite was made during an
attack or as a scavenging mark.  Too bad, but it looks like we have to
fall back on our null hypothesis again.

Evidence 4: Tenontosaurus is too big for one dromaeosaurid to handle.
 Pack hunting was obviously necessary to bring them down.  Well, okay,
but this assumes that Deinonychus had pack instincts, something we
can't directly observe.  Plus, maybe once a Tenontosaurus got big
enough, it was left alone.  Maybe if Deinonychus was a pack hunter, it
attack juvenile Tenontosaurs.  And, it turns out, a subadult
Tenontosaurus MOR 682 at the Museum of the Rockies was found in close
association with 11 shed Deinonychus teeth.  The skeleton appears to
have ripped apart pretty good by some dinosaurs and perhaps this
indicates that many Deinoychus were employing pack tactics to bring
this smaller guy down.  Or, this smaller guy was killed by a bigger
theropod and then scavenged by Deinonychus.  Or, this smaller guy died
of other causes and was later consumed by Deinonychus.  And even if
these animals didn't have pack behavior, they could be drawn to a
stinking carcass like vultures.  So again, our evidence is equivocal. 
We fall back on our null hypothesis yet again.

Well, we could go on like this for a long time, but I hope you see
the point I'm trying to make.  As scientists, we are duty-bound to be
skeptical of every new (or even not so new) claim until we find
evidence that positively supports that claim, or hypothesis.  And
remember, every hypothesis and theory in science, in order to be
scientific, has have these four qualities: 1) It has to be testable;
2) It must be repeatable by other researchers; 3) It must be
falsifiable; and 4) It should have predictive power.

Science is a tough business, and paleontology is extra hard because
we don't have as much control over the evidence as do some
experimental scientists.  Even though it would be awesome if theropods
hunted in organized packs, dispatching hadrosaurs and sauropods left
and right with cool, calculated efficiency, we just don't have enough
positive evidence to say, definitely, yes this is what happened.

But this is where you come into the picture.  How badly do you really
want to know and see and touch the real evidence?  Maybe there's
something the scientific community is missing, or hasn't considered,
or hasn't looked at, or who knows?  New technology may come along to
help us address questions we can't even fathom answering or even
asking now.  If you want to become a paleontologist, maybe you can put
your mind toward figuring out just what the behavior of dromaeosaurid
theropods was like.  It will take a lot of math, anatomy, physiology,
ecology, behavioral studies, geology, and even more determination and
perserverance.  And maybe after all that you will still not know the
whole story.  That's the risk but that's also your chance to possibly
change the way we currently look at theropod behavior.

Finally, I should add that some of the information above I got from
the following sources.  It's important, where ever possible, to give
credit to previous researchers, even if you don't agree with their
conclusions.  Good luck with your question, and feel free to ask more.
 On this list, we can't always return responses right away (most of us
our very busy with our research, teaching, and other stuff) but don't
be discouraged.  At the very least, use the library frequently and
always look for evidence that does not confirm your ideas.

Forster, C. 1984. The paleoecology of the ornithopod dinosaur
Tenontosaurus tilletti from the Cloverly Formation, Big Horn Basin of
Wyoming and Montana.  The Mosasaur, 2: 151-163.

Glut, D. 1997. Dinosaurs: The Encyclopedia. North Carolina: McFarland
& Company, Inc., Publishers.

Maxwell, W. D., and J. H. Ostrom. 1995. Taphonomy and paleobiological
implications of Tenontosaurs-Deinonychus associations. Journal of
Vertebrate Paleontology, 15(4): 707-712.


2nd E-mail:
Megaraptor:

Okay.  You said:
"If you look at the evidence of other Tenontosaur sites, the amount
of
teeth is amazing.  The teeth alone should be some sort of evidence
that
at least D.antirrhopus was a pack hunter."

That was part of my point with Evidence 2 and Evidence 4, but let's
take this a step further.  If you were another paleontologist and said
what you did above, I would ask you, "How many teeth is a lot?  The
teeth alone cannot be evidence for pack behavior by themselves because
you have no way of showing me which teeth came from which dinosaurs. 
Maybe one or two dinosaurs lost their teeth, or maybe five or six like
you say.  How can know for sure?  All the teeth seem to show is that
one or some Deinonychus shed their teeth near the carcass, MAYBE
because they were eating it.  You can speculate that it was a pack
attack, but the teeth alone don't convince me.  Alligators and
crocodiles shed their teeth all the time when they attack and feed,
and they're definitely not pack hunters."

You said:
"A D.antirrhopus hunting party of about five
individuals couldn't take out a healthy adult Tenontosaur, they
could
only take out the weak, sick and young, as many group hunters today
do.
D.antirrhopus wasn't always successful in its kills as seen at the
Tenontosaur and D.antirrhopus site, at least four individuals died
in
the attack."

If I were going to argue this with you as another paleontologist,
here is what I would say: "You have no evidence for what you say,
although it sounds very interesting.  How do you know they hunted in
packs?  What are you basing your claim about a hunting party of 5 on? 
The group hunters you refer to are mammals, not birds or reptiles, so
why do you think the D. antirrhopus would operate the same way?  How
did you count the four individuals that you say died in the attack? 
How many bones of each Deinonychus did you find?  How do you know the
bones of the Tenontosaurus and Deinonychus didn't get washed
together?"

Please don't take these questions as criticisms of you.  I like the
idea that theropods hunted in packs.  I'm just trying to show you that
it's not that simple.  It's harder to figure these things out than you
might guess from reading about these things.

As far as what you said here:
"Not all theories are able to be tested, it is a theory that T.rex
was a
scavenger but there is no way of testing that. (But that's a post
for
another time.)"

If you cannot test something, it is speculation, not a scientific
theory or hypothesis.  I'm sure you've heard people say, "I have a
theory that ..." or "My theory is ..." but usually what they mean is
speculation.  And it depends on what you mean by "tested."  Can we go
back in a time machine and see what a T. rex did?  Of course not! 
But, we can phrase the question so we can test it.  Perhaps we can ask
why the skull of T. rex is so large and robust.  Perhaps we could
address why it has the small arms it has.  Perhaps we could look at
modern scavenging and predating mammals, birds, and reptiles, look at
the adaptations in their skeletons for scavenging or predating, and
see what we can in a T. rex.  And keep in mind, all predators scavenge
at times.

So part of your problem would be separating opinion or speculation
from the actual data we can observe and test.  For instance, the
evidence is that some Tenontosaurus specimens have been found in
association with Deinonychus teeth, and even more rarely with some
FRAGMENTS of Deinonychus bones.  That's the evidence.  The speculation
is that the Deinonychus MAY have formed packs and MAY have been killed
while trying to kill this dinosaur, but again this is speculation, not
theory.  If you cannot test it, it cannot be a scientific theory.  You
may know that a Velociraptor was found wrapped around a Protoceratops
in Mongolia.  That's the kind of evidence I would want to see, but in
your case, I would want to see several Deinonychus wrapped around a
Tenontosaurus before I was convinced.

Finally, you said:
"Will we ever know the whole story to the dinosaurs?  I sure don't
think
so."

How can you give up hope so fast?  And what do you mean by the whole
story?  If you mean we will ever know each and every single dinosaur
and what it did and what it looked like, maybe not.  But every day
something new or interesting is discovered in the ground or in a
museum collection, some paleontologist comes up with a new way of
looking at things, etc.  You never know what we will ultimately find
out about dinosaurs, and you always have to keep hoping that maybe,
someday, we might be able to know everything we ever wanted to about
dinosaurs.  Yes, this is probably a dream, but there is an awful lot
of work yet to be done, not only on dinosaurs not discovered yet, but
also on the ones sitting under our noses.

I have a suggestion: before you respond again, start asking the
questions I asked you above when you go back and read these books and
magazines you're getting your information from.  If you can't find the
answer there, look at other books, and try to read things by other
scientists who might have a different opinion.  If you're really
brave, write a letter to one of the scientists whose book you are
reading, and ask them some of your questions, and see what happens.

Good luck.

Matt Bonnan