majority of the 17 species of penguins do not live in Antarctica but
rather between latitudes 45° and 60° S, where they breed on
islands. A few penguins inhabit temperate regions, and one, the
Galapagos penguin lives at the Equator. Evidence from paleontology and
genomic studies indicates that penguins and Procellariformes
(albatrosses, shearwaters, and petrels) had a common origin. Both
groups are represented by well-defined fossils dating to about 50
million years ago.
The penguins are highly specialized for their flightless aquatic
existence. Their forelimb is transformed into a paddle. The feet are
located much farther back than those of other birds, with the result
that the bird carries itself mostly upright. The sole comprises the
whole foot instead of just the toes, as in other birds.
Insulation of the bird's body is particularly important for Antarctic
species that live in water that is always below 0 °C (32 °F).
With a wind of 110 km (70 miles) per hour, the cooling power of
seawater at −1.9 °C (28.6 °F) is equal to that of a
temperature of −20 °C (−4 °F) . The skin is
insulated by a layer of air trapped under the plumage, and the only
bare skin in direct contact with the water is that of the feet. There
is a remarkable anatomical arrangements in the lower limb, whereby
closely adjacent arteries and veins form a system of heat exchange
between opposing flows of blood.
penguin. (2011). Encyclopædia Britannica Ultimate Reference Suite. Chicago: Encyclopædia Britannica.