Geoscience Reference
In-Depth Information
the eggs resulting from a mate that she regards to be more fit than the
others. We don't know whether sauropods also behaved like this,
although it is possible since mallards and sauropods are both
dinosaurs. Nonetheless, such factors may account for the variations we
observed at Auca Mahuevo.
Additionally, we wondered how variations in environmental factors
might come into play. As mentioned earlier, dinosaur eggshell is
made of calcite, which is highly soluble in water. After the eggs were
laid, dissolution by rainwater or subsequent exposure to groundwater
after burial could have altered the surface ornamentation of the
eggs, eroding or accentuating ridges and valleys. The eggs from Auca
Mahuevo have been at the mercy of such conditions for millions of
years, so it seems reasonable to expect that some dissolution could
have occurred. So, until we discover an egg with a different kind of
embryo inside or one with distinct differences in its microstructure, we
think it is more reasonable to suggest that all the eggs from all the rock
layers at Auca Mahuevo came from the same species of sauropod.
This was not the first time that paleontologists had suggested
that sauropods returned to a particular nesting site. In 1995, for
example, paleontologists working in the southern Pyrenees Mountains
of Spain reported that they had found a site that also contained sev-
eral clusters of dinosaur eggs in one layer of red sandstone. The eggs
were almost spherical and slightly larger than the Auca Mahuevo
eggs, averaging about eight inches in diameter. Although no embryos
were found inside the eggs, they were assumed to belong to sauropod
dinosaurs.
At this Spanish site, the organization of the sand grains within the
layer that contained the eggs suggested that the sandstone had been
deposited by waves along the shoreline of an ancient ocean. Although
initial studies concluded that the dinosaurs had nested on this beach,
subsequent examination of the rock layers containing the eggs demon-
strated that the ocean had retreated from this ancient shoreline by the
time the dinosaurs had laid the eggs. Fossils from the sandstone and
other nearby rock layers indicated that these alleged sauropods had
used the site sometime between about 71 million and 65 million years
ago, making it slightly younger than our Patagonian site.
Across one area of about six thousand square yards, the collectors
documented twenty-four egg clutches arranged in three clusters.
