that the eggs actually were in the bottoms of ancient channel depressions. This means that the eggs were likely transported from their original nests and might also have more than one species of dinosaur represented. Whether their original makers were sauropods or other dinosaurs is still unknown.
The nests recently discovered in Patagonia, some of which are definable as mound structures with upraised rims, are in multiple horizons of the same relatively small area (about 2.5 km2), indicating site fidelity. Site fidelity means that the sauropods, represented by an unidentified species of titanosaur, came back to nest in the same place over multiple breeding seasons. The eggs in these horizons number in the thousands. The embryos are exquisitely preserved and some show skin impressions, the only ones known for any dinosaur embryos. Not only do these eggs provide a rare glimpse into the life history of a titanosaurid, but they are the same size and morphology as some of the previously unidentified Cretaceous dinosaur eggs found in such widely separated places as China, India, Europe, and Africa. (Fig. 10.10). This similarity may serve as a model for comparison and thus aid in the identification of other sauropod nests and embryos in the future. Furthermore, the nest structures, which were probably constructed by the sauropods, can aid in identifying other sauropod nests in the absence of eggs or embryos. This same search image serves as a tool for identifying some thero-pod nests as well (Chapter 9).
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