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made by theropods like
Troodon
and some sauropods also imply that these dino-
saurs dug up and mounded soil to make these protective structures.
Related to this, a renaissance in our understanding of dinosaur eggs, babies,
and the rearing of young has revolved around their trace fossils, too.
Troodon
, a
Cretaceous dinosaur from 70 to 75 million years ago and found in parts of western
North America, was the first known North American example of a theropod that
made rimmed ground nests. These nests also contained clutches of paired eggs,
which were arranged vertically in the nests by one or both of the parents after egg-
laying. All three trace fossils of
Troodon
behavior—the making of rimmed ground
nests, pairing of the eggs, and their post-laying arrangement—provide insights we
never would have figured out from their skeletons.
Similarly, a spectacular find of Late Cretaceous nests in Argentina from 70 to
80 million years ago and attributed to gigantic sauropods called titanosaurs shows
that dinosaurs other than
Troodon
made ring-like enclosures for their eggs. The
sauropod nest structures, however, only superficially resemble those of
Troodon
and are bigger, more abundant, and stacked on top of one another, representing
many episodes of sauropod breeding in the same general area. In this sense, then,
didtheseenormousdinosaursactlikemodernmigratorybirds,returningtothesame
nesting grounds for hundreds of thousands of years? Once again, this and other
questions are ones that trace fossils can help to answer.
Theseeminglyodddepictionoftheganglytheropod
Struthiomimus
consuming
rocks along a riverbank and using these as gastroliths is not too far off from the
truth, either. Paleontologists have long suspected that some herbivorous dinosaurs,
similar to modern birds or crocodilians, swallowed rocks and used them in their
digestive tracts to grind food. This especially made sense for dinosaurs with teeth
poorly adapted for chewing yet somehow needing to eat difficult-to-digest plants.
What has surprised paleontologists in recent years, though, is the realization that a
few theropods, a group of dinosaurs once assumed to have been exclusively carni-
vorous, also have these “stomach stones.” Paleontologists just assumed that strong
