Putting It All Together

figure 17-7

To classify an organism and represent its systematics in an evolutionary context, biologists use many types of information to build and revise phylogenetic models. Systematists will use data about physical features, embryos, genes in the nucleus, mitochondrial DNA, and ribosomal RNA.

Consider the classification of pangolins that is shown in Figure 17-7. African and Asian pangolins share several adaptations with other mammals that eat ants, including African aardvarks and South American anteaters. These adaptations include narrow snouts, strong digging claws, and long, sticky tongues. These shared characteristics, however, are analogous, not homologous. Deeper analysis of other characteristics, such as skeletal structures and nucleotide sequences in several genes, indicate that all three anteating taxa—pangolins, anteaters, and aardvarks—occupy quite different branches on the mammalian phylogenetic tree. Therefore, systematists place pangolins closer to the group that includes dogs and bears than to either aardvarks or anteaters.

This phylogenetic diagram is based on analyses of the DNA of many kinds of mammals. These analyses do not support a systematic grouping of pangolins with either African aardvarks or South American anteaters. Instead, pangolins seem to be most closely related to carnivores, such as bears and dogs. Biologists sometimes revise their classifications in light of such new evidence.

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