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Understanding evolutionary relationships is an important part of the discipline of systematics (the scientific classification of organisms)....

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Figure 1.Phylogenetic tree showing the relationships among six vertebrate organisms. Depicted are a shark and the mammals dog, dolphin, and three fossil organisms from the Eocene Epoch (34–55 million years ago) that are thought to be closely related to living whales. Note that Ambulocetus had fully developed legs. Two groups of vertebrates, sharks and whales, have torpedo-shaped bodies. Comparative data, however, suggest that this body shape evolved convergently (independently) in each of these groups.

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Figure 2.Phylogenetic tree of amniotes. It is derived from morphological character data that come from both fossil and living organisms. The same tree was recovered after molecular sequences were added to the morphological data. Skeletal silhouettes represent fossil species; body silhouettes represent living species. Although birds and mammals are both warm-blooded, this phylogeny suggests that each developed that feature convergently (independently). (Adapted from J. Gauthier et al., 1988)

From update 'Evolutionary relationships'

evolutionary tree

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