Geoscience Reference
In-Depth Information
CHAPTER
ELEVEN
Was the Nesting Site
Used More than Once?
Discovering New Egg Layers
Our primary goal in undertaking the second expedition was to gain a
better understanding of the reproductive behavior of sauropods.
Given the evidence that was preserved in the rocks at the site, the
answer to one aspect of this behavior had become clear. Many mod-
ern animals return to the same area to lay their eggs during different
breeding seasons. Did the ancient giant dinosaurs of Patagonia do this
also?
The evidence to answer this question was in the stratigraphic sec-
tion that showed all of the different rock layers exposed at the site. To
make the drawing, Lowell began at the lowest rock and worked his way
up, layer by layer, to the highest. He had taken great care, when com-
piling the section, to record the color, thickness, rock type, and fossil
content of each layer of rock that he found, not the most exciting job
in the world even for a geologist. In all, the layers of rock that crop out
at Auca Mahuevo are almost five hundred feet thick, and there are
more than thirty-five distinct, major rock layers. The project took more
than a week, but in the end, this hard and sometimes tedious work
paid off. With all this geologic data recorded in his notes, we could
now determine how many different layers of rock contained sauropod
eggs, which would provide the clues we needed to decide if the
sauropods had used this nesting site more than once.
As we mentioned earlier, this sequence of rock layers is important
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