Bock, Walter J. Department of Biological Sciences, Columbia University, New York, New York.
Last reviewed:February 2018
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A small monotypic order of flightless, marine swimming birds, comprising the penguins, found predominantly in the colder southern oceans. Penguins (Fig. 1) constitute the order Sphenisciformes in the class Aves. Depending on the classification scheme, there are about 17 to 19 species of penguins. These aquatic, flightless birds most likely evolved from members of the order Procellariiformes, perhaps from a diving petrel-like ancestor. Classification schemes that hypothesize a link between penguins and loons (order Gaviiformes) have no factual support. At one time, members of the present Sphenisciformes had been placed in a separate superorder, Impennes, but such a designation suggested too great a divergence of the penguins from their ancestral group of tube-nosed swimmers. Some taxonomists have enlarged the Ciconiiformes to include the Sphenisciformes, as in the Sibley-Ahlquist taxonomy [a radical new approach to taxonomy, based on deoxyribonucleic acid (DNA) hybridization studies]. See also: Animal evolution; Aves; Ciconiiformes; Gaviiformes; Procellariiformes; Taxonomy
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