Geoscience Reference
In-Depth Information
some embryonic bones. Luis and a few others tried to estimate how
many eggs and nests were exposed on a small portion of the flats by
tying colored tape to the branches of some small bushes to mark out
a trapezoid and measuring the distances between bushes using the
GPS. With this information, they calculated that the two sides were
about 1,000 feet long, with the top about 250 feet across and the base
about 400 feet. Within that area they counted about 195 clusters of
eggs. Later, we would refine the estimates, but the number of egg clus-
ters would still be extraordinary.
The abundance of eggs triggered a lighthearted discussion among
our crew members regarding what we should name our new fossil
site. After brainstorming over several humorous possibilities, we all
agreed on a name—Auca Mahuevo. In part, the name represented a
pun on Auca Mahuida, but it also acknowledged the seemingly
countless number of eggs preserved at the site.
Mahuevo
is kind of a
Spanish contraction for
mas huevos,
which means "more eggs."
As part of our prospecting for eggs and embryos, we walked many
miles over the flats and adjacent ridges. The layer with eggs seemed to
go on forever. Many thousands of nests were spread over several square
miles. But all the eggs seemed to be restricted to a single layer of rock.
Noting this relationship, Lowell began studying the rocks that
contained the fossils, intent on finding clues that would shed more
light on the dinosaurs that had lived at Auca Mahuevo. The beauti-
ful reddish brown mudstones, as well as distinctive greenish sand
layers that were mixed in with them, might provide important evi-
dence to help us interpret what kind of environment the dinosaurs
were living in, as well as how long ago they had lived.
Lowell's most important geological job was to start at the bottom
of the sequence of rock layers and measure the thickness of each layer
of sandstone and mudstone. As the measurements were taken, he drew
a picture of the different rock layers in his field notebook. That
depiction is called a stratigraphic section. These drawings are impor-
tant for telling time back when the dinosaurs were living at the site.
Based on previous work done by other scientists, Lowell knew that the
rocks at Auca Mahuevo were deposited sometime during the latter
stages of the Cretaceous period, between about 70 million and 90 mil-
lion years ago. But his challenge was to find evidence that would spec-
ify the age more precisely within that long interval.
