Think About It

The Worldwide Distribution of Dinosaurs

The subject of bias in the fossil record was discussed in Chapter 2. One factor affecting the discovery of fossils is whether the proper sedimentary layers of the Earth are accessible to people who are looking for fossils. Earth's crust is a moveable layer that consists of tectonic plates. Geologic forces slowly change the surface of the Earth by pushing these plates together, folding them over and under themselves, raising older layers to the surface, and pushing more recent layers down below. As a result, some ancient layers containing dinosaur fossils that have been buried by millions of years of sedimentation find their way to the surface, where erosion can expose evidence of ancient life.

Just where such fossil exposures are located is key to the success of paleontology. Relying on geologic maps that have been created during the past 200 years, paleontologists seek areas to explore that are likely to contain sedimentary rocks—and, hopefully, fossils—from the span of time that interests them.

was a hunting pack, it is conceivable that these large predators worked together to bring down such gigantic prey as the sauropod Argentinosaurus, which also lived in the area at the same time.

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