Sphenisciformes
Article by: Walter J. Bock, Department of Biological Sciences, Columbia University, New York, New York.
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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 desig-
nation 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 taxono-
my, based on deoxyribonucleic acid (DNA) hybridization studies].
Characteristics
Penguins are medium-sized to large birds. They are completely flightless, with their wings
having been modified into stiff flattened flippers. They stand upright on legs that are
placed far posterior and that terminate in four toes; the anterior three toes are webbed.
Penguins swim and dive well, using only their wings for propulsion: their feet are used only
for steering during swimming. Terrestrial locomotion is by walking, hopping, or sliding on
the belly while pushing with the wings. The plumage consists of dense scalelike feathers
that are black dorsally and white ventrally. A distinctive pattern or crest, often yellow, oc-
curs on the head (Fig. 1).
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Content
• Characteristics
• Habitat
• Fossil record
Fig. 1: Aptenodytes patagonicus, the king penguin.
(Credit: Gerald and Buff Corsi; copyright © California
Academy of Sciences)
Key Concepts
• The sole members of the taxonomical order Sphenisciformes are penguins, which
chiefly inhabit the colder southern oceans.
• Penguins are medium-sized to large birds, but are flightless. Their wings have been
modified into stiff flattened flippers, enabling them to swim.
• Socially, penguins are gregarious and breed in large colonies along coastal areas.
• Male and female penguins form strong pair bonds and share in the incubation
and care of the young.
• Fossils of penguins have been found in Antarctica, Australia, and South Africa,
approximating the range of present-day species.
