Geoscience Reference
In-Depth Information
Granger brought in ... a part of an eggshell which we supposed was
a fossil bird, but which subsequently was recognized as dinosaurian....
We could hardly suspect that we should later consider this the most
important [site] in Asia, if not in the entire world.
The skull that Shackelford had found turned out to belong to a
primitive new member of the horned dinosaurs, and the eggshell that
Granger had found following Shackelford's route led to the discovery
of numerous nests of dinosaur eggs. These were the ones that Andrews
and his team originally thought belonged to
Protoceratops,
but were
later recognized as belonging to a dinosaur related to
Oviraptor.
Having determined, with Brooks's help, that more than one layer
of eggs was present at the site, we now needed to make sure that no
others were present. We examined the layer containing the eggs on
the flats in more detail. Was there really just one thick layer or were
several layers closely packed together? In March 1999, Lowell and
Julia Clarke spent two whole days walking around the flats and the
ridges that rimmed them. This careful investigation revealed two sep-
arate layers of eggs in the mudstone, separated by four thin layers of
sandstone, siltstone, and mudstone that together were about five feet
thick. The lower layer did not contain nearly as many eggs as the
upper layer, but it represented a different and slightly earlier page in
the history of the site. Our survey of the flats also showed that both
of these layers of eggs were well below the younger layer that Brooks
had found. Perhaps these two layers of eggs were laid within years or
decades of one another, but again we cannot be certain.
In addition, Lowell found another single cluster of eggs in a fourth
layer about twenty-five feet below the lowest layer of eggs exposed on
the flats. Not much of this layer is exposed because it lies right on the
desert floor below the ridges and flats. Nonetheless, we know that the
eggs were not washed down from the adjacent egg-bearing areas
because they are complete and planted firmly in the ground, rather
than sitting isolated on the surface.
Finally, Frankie's mapping of eggs at the quarry, along with statis-
tical analyses of their distribution, which we will describe later, sug-
gested that two different levels of eggs were probably present there.
This means that at least four, if not five, different layers of sauropod
eggs are present at Auca Mahuevo.
