All penguins, living and extinct, are included in the Spheniscidae family classification. This is the only family classification in the order Sphenisciformes. There are at least 17 known species of penguins. Penguins are flightless, marine birds that have adapted to the cooler waters of the southern hemisphere.
All penguins have a similar torpedo shaped body, which varies in size between species.
The wings of penguin are stiff paddle like flippers that help them navigate the sea. To help them remain submerged underwater and conserve energy during diving the bones of a penguin are heavy and solid. Penguins have densely packed, shiny feathers that help insulate them from the extreme cold that they may encounter. Penguins actually have more feathers than most birds, approximately 70 feathers per square inch. Most species go through a complete molting once a year.