Adaptive Radiation and Convergent Evolution

What are two patterns of macroevolution?

As paleontologists study the fossil record, they look for patterns. Two important patterns of macroevolution are adaptive radiation and convergent evolution. As you'll see, Darwin noted both patterns while aboard the Beagle.

Adaptive Radiation Studies of fossils and living organisms often show that a single species or small group of species has diversified over time into a clade containing many species. These species display variations on the group's ancestral body plan, and often occupy different ecological niches. These differences are the product of an evolutionary process called adaptive radiation. Adaptive radiation is the process by which a single species or a small group of species evolves over a relatively short time into several different forms that live in different ways. An adaptive radiation may occur when species migrate to a new environment or when extinction clears an environment of a large number of inhabitants. In addition, a species may evolve a new feature that enables it to take advantage of a previously unused environment.

▸ Adaptive Radiations in the Fossil Record Dinosaurs—one of several spectacular adaptive radiations of reptiles—flourished for about 150 million years during the Mesozoic. The fossil record documents that in the dinosaurs' heyday, mammals diversified but remained small. After most dinosaurs became extinct, however, an adaptive radiation of mammals began. That radiation, part of which is shown in Figure 19–11, produced the great diversity of mammals of the Cenozoic Era.

FIGURE 19–11 Adaptive Radiation This diagram shows part of the adaptive radiation of mammals. Note how the groups of animals shown have adapted to many different ways of life—including two groups which have become aquatic. Interpret Visuals According to this diagram, which mammal group is most closely related to elephants? Does this surprise you? Explain.

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