Geoscience Reference
In-Depth Information
For the sauropods, however, this is not so clear. Some researchers
believe that, because the eggs are laid so close to one another, the huge
size of the adults would prevent them from directly taking care of their
own young. Furthermore, the rarity of hatchlings or juveniles in the
nesting grounds containing sauropod eggs is considered to suggest
extreme precociality, meaning that as soon as the sauropod embryos
hatched, they left the nesting area and moved to feeding grounds.
Although we have found many embryos at Auca Mahuevo, we have
not found any well-preserved hatchlings or juveniles in the same
rock layer with the eggs. Anwar Janoo found a few small bones that
might be from a sauropod hatchling on top of a clutch near the egg
quarry in 1999, but they were too poorly preserved for us to identify
them with any certainty. If the paucity of hatchlings and juveniles is
a real representation of what was happening at the nesting site, and
not a misleading problem with the way fossils became preserved,
our inability to find juveniles may support the conclusion that
sauropods were very precocial. One possibility was that, shortly after
hatching, the baby sauropods congregated in large numbers, forming
herds equivalent to flocks of hatchlings of flamingos and some other
kinds of birds. These juvenile flocks, usually called creches, are
guarded by a group of adults. The same could have been true for the
giant sauropods. This idea may explain why sauropod bone beds and
herd trackways rarely contain fossils of hatchlings or small juveniles.
In any case, we had plans to test this idea. And where better than in
the richest sauropod nesting site yet discovered—Auca Mahuevo.
Our examination of the scientific literature revealed that most, if
not all, of these ideas about the reproductive biology of sauropods had
been reached with little supporting evidence. Speculation about colo-
nial nesting and territoriality in sauropods had been based on a lim-
ited number of nests, and as we have discussed earlier, without even
knowing the true identity of the eggs. We felt that Auca Mahuevo,
with its extensive egg layers laid by one kind of sauropod, provided a
unique opportunity for sampling and measuring the eggs at the site,
which could in turn shed new light on these and other issues concern-
ing sauropod nesting behavior. The crucial evidence to resolve these
issues lay in how the eggs were distributed in the egg layers.
As mentioned earlier, we undertook two projects to determine
the distribution of eggs at Auca Mahuevo. The first involved exca-
