Geoscience Reference
In-Depth Information
CHAPTER
TWELVE
Were Giant Dinosaurs Gregarious?
Our Nests of Eggs and Other Evidence
Some animals are gregarious, whereas others live more solitary lives.
How did the giant sauropods behave, especially when they went to the
nesting site at Auca Mahuevo to lay their eggs? It had previously been
suggested that sauropods laid their eggs in enormous colonies. The
studies of the Indian and Pyrenees egg sites, mentioned in the last
chapter, documented that thousands of eggs had been laid in areas
encompassing several square miles. To the paleontologists studying
those sites, this suggested that the area represented a single enormous
nesting ground. In addition to speculating that the sauropods of
India and the Pyrenees may have returned to the site during several
breeding seasons, the scientists concluded that the close spacing of the
nests might be indicative of some territorial behavior among indi-
vidual sauropods. This seemed reasonable to the researchers because
the eggs and nests were fairly well preserved, which suggested that the
mothers had not trampled the clutches of eggs while moving around
the site. But this evidence for colonial nesting and territoriality did not
satisfy many researchers in the field of dinosaur reproductive biology.
Notwithstanding such criticisms, evidence from fossilized foot-
prints and bone beds (high concentrations of skeletons from a single
dinosaur species in a single rock layer) has also been used to suggest
that at least some sauropod dinosaurs were gregarious. The best evi-
dence for this comes from what are known as trackways, sequences of
fossilized footprints left by sauropods in soft mud and sand, which
later hardened into rock after the layer of soft sediment was buried.
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