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back to science



In response to the less than subtle request to get back to scientific
discussions, I would like to propose the following.

First, here are some facts that I take as givens.  The European sauropod
Hypselosaurus was about 40 feet long and produced eggs about a food in
diameter.  Trackways show some sauropods moving in groups which included
fairly small individuals.  Sauropods were faced with a variety of
predators, some of which were considerably larger than a neonatal sauropod.

Now then, from these flimsy pieces of evidence and adding a few assumptions
I would propose the following.  Sauropods were highly social animals,
living in close-knit groups.  They reproduced infrequently, and at any
given time there were few juveniles in a group.  Occasionally a female
would lay a small group of eggs in the spring, to coincide with the
appearance of new shoots.  She covered them with dead vegetation, which
provided the heat for incubation.  As the eggs developed, the group stayed
in the vicinity, with one individual always staying on guard while the
others brought it food.  Predators would have had difficulty digging into
the nest mound before swift and deadly action came from the nest guarder,
in the form of a kick, stomp, or crushing blow with the head.  The eggs
developed quickly, like bird eggs, the baby sauropods hatching in a fairly
precocial state.

Once the baby sauropods hatched, they were kept toward the center of the
group.  The adults picked succulent tips of vegetation and gave them to the
babies, which grew rapidly.  By summer the babies were the size of elk, and
well able to keep up with the group under normal circumstances.  The adults
were feeding them much less by this time.  By fall they were half the size
of the adults, and well able to defend themselves.  As the group migrated
to its winter range, the young sauropods had no difficulty keeping up.

These sweeping conclusions are (I hope) bold, provocative, and some would
say, untestable.  With this last I do not agree.  In any case, here is my
rationale.  The extremely large size of adult sauropods combined with their
endothermy means that they could not go without food for long.  The fact
that they laid such small eggs is due to their inability to put much energy
into reproduction; attempting to store energy would only have compounded
their mass problem and made them less efficient.  At the same time, their
young could not survive on their own amongst the speedy, voracious
predators of their day.  This precluded a lay them and leave them strategy.
 (Actually, no living archosaur descendant to my knowledge has such as
strategy, so it is doubtful whether any dinosaur did.)  The need for adults
to feed at high rates meant that only a few babies could be cared for at
any given time.  If sauropods were not social, individual pairs would have
had to care for highly vulnerable hatchlings for months at a time.  While
one parent guarded the young, the other would have had to collect enough
food for the guarding parent, a virtual impossibility for an animal that
could barely supply its own needs.  The solution was to live in groups,
with only one or two individuals in the group reproducing in a given
season.  Since adult sauropods had a constant need to be free of as much
mass as possible, they would not have evolved viviparity.  Yet they were so
much larger than their eggs they could not have used their bodies to
incubate them.  The need to be free of the burden of rearing young and the
need for the young to lose vulnerability made for rapid development of both
eggs and neonates.  Detection of and defense against predators would have
also been vastly improved by sociality.

In E.O. Wilson's reconstruction of a Diplodocus herd (based on Bakker and
Ostrom's papers) he assigned them a level of sociality similar to that of
African elephants.  Actually, they were quite different from elephants in
that their young were relatively small at birth.  But I believe Wilson's
reconstruction is substantially correct.  

I would appreciate feedback.

Best regards,

Dave