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More on Gangs, packs, etc.



Brian writes:
"Would you also conclude that with such reptilian-sized brains, the
amount of 
learning and complex behavior ability needed to form herds was not
present in 
most herbivorous dinosaurs?  Naively, it seems that if herds existed
this 
would be an argument in favor of packs."

Ah, yes!  You got me ... well, sort of.  In thinking along
theropodian lines only, I neglected to consider the evidence from
herbivorous dinosaurs, especially hadrosaurs.  Hmmmm ...

Using crocodilians and birds as my phlyogenetic bracket again,
communal behavior is definitely present in many birds and some
parental protection and nest guarding behavior is present in
crocodilians.  Yeah, but I'm waiting for someone to say, "Hey, aren't
these just anecdotes too?"

Birds have two types of chicks -- precocial and altricial.  (For
those on this list who may not be familiar with these terms, precocial
means that the bird hatches out almost like a small adult, ready to
walk and get food on its own (baby ducks); altricial are chicks born
without the ability to move or follow the parent to forage when
hatched, and these are like sparrow babies which chirp incessantly for
the parent to bring food to them.)

With Maiasaurs, Jack Horner and others were able to show that there
were small juveniles in the nests with under-developed bones.  It was
argued that these dinosaurs were altricial, and that the parents would
have had to feed and protect their young in these cases until the
animals were old enough to move along on their own.  This, along with
the nesting site, etc., is pretty decent physical evidence for
parental care and some degree of herding behavior in those dinosaurs.

I am unaware of mass nesting sites and altricial juvenile fossils
being found for predatory dinosaurs (right, absence of evdience ...). 
However, the point of my posting was that it seems a stretch to equate
predatory dinosaurs with packs of mammals.  And that congregations of
birds and other archosaurs are not like those of most mammals.  The
brains of archosaurs and mammals are quite different -- many birds
imprint on whatever they first see as their mother and, while some
birds can be extremely intelligent and clever, most are very
hard-wired organisms set from the get-go with their birdy-program of
how live a bird's life.  'Gators and crocs appear to much the same
way.

There is no reason that communal nesting and herding behavior cannot
evolve with archosaur circuitry, but I still assert that "packs" of
predatory dinosaurs in the "mammalian sense" is a great concept but
lacking in physical evidence.  We know that most dinosaurian brains
fall in the range of reptiles (not even birds!), so it would seem
reasonable until more evidence presents itself to regard the complex
mammalian pack hunting systems and communities as something unique to
mammalian evolution and look to alligators and crocodiles for a more
realistically constrained model of dinosaur behavior.  This is not an
indictment of reptiles or archosaurs.  I keep snakes as pets, and they
fascinating creatures that I respect greatly for the patience and
quick strikes in obtaining "intelligent" mammalian prey.  But I don't
keep snakes for companionship ...

The danger with using modern relatives as analogs to dinosaur
behavior is taking the analogy too far.  If we view dinosaurs as
reptilian mammals in our mind's eye, we seem likely to bestow
mammalian qualities upon them.  If it is birds we choose, again those
qualities are transferred.  Or reptiles.  The physical evidence for
communal nesting and herding is excellent in some hadrosaurs.  The
trackways of sauropods show that some of them at least headed in the
same direction, and this might be indirect evidence of some level of
herding.  And we do have that new nesting sauropod site.

But you can hold an endocast of a sauropod brain in the palm of your
hand, and the cerebrum is demonstrably tiny.  I love sauropods to
death, but I must admit they were probably none too bright.  Yes, they
may have formed herds, but what sort of structure was there?  Would
anyone argue that there was a matriarch, like in elephants, or to
stretch it further, that there was the "sauropods' graveyard" where
sauropods went to "mourn" their dead?  Since sauropods laid eggs and
did not give live birth, was the reproductive rate high enough that,
unlike the low reproductive fecundity of elephants, protection of the
young was not as crucial to their survival?  If you lay on average
8-10 eggs a year, as long as one of your offspring survives is that
all that matters?  And if so, would sauropod "herds" simply be loose
congregations of herbivorous dinosaurs, finding safety in numbers
until large enough that predators were no longer a threat?  

What of ornithischians, who were not saurischians and therefore have
no living descendants?  Are we sure that by examining birds and crocs
that we can evaluate their behavior?  Luckily, we have the nesting
sites and altricial-appearing young, but, as with the sauropods, what
kind of herds were they?  And, since theropods are saurischians, one
could even argue (on no evidence, of course) that ornithischians were
different enough from theropods that they could form more complex
herds than was possbile in theropods.  The speculations, as always,
are endless.

My own philosophy (read opinion here if you like) is that when one
approaches the study of any dinosaur to treat the animal like it is an
alien within the vertebrate framework.  Examine the anatomy, the
articulations, the sedimentology of the animal's resting site, etc. 
THEN, when something strikes you as interesting or strange, look to
other vertebrates for similar examples.  And be prepared not to find
anything quite like it.  The problem (in my humble opinion) appears to
be looking for analogs, applying them to dinosaurs a prior, and then
searching for evidence to support the "obvious" nature of whatever it
is you want them to be.

If we only had a time machine ... =)  And notice that I leave the
Coelophysis (or Rioarribasaurus???) Ghost Ranch site open for any
takers ... =)

Matt Bonnan
Dept. Biological Sciences
Northern Illinois University