The Body: Parts & Functions

Trading off between flying and swimming
Flying and swimming do not mix well. Flying requires light bodies with large, flexible wings and swimming requires heavier bodies with stiff, short wings. Ancient penguins lost the ability to fly by becoming heavier and developing a skeleton better adapted for swimming. There are many other consequences of this trade off as well. Explore the anatomy of penguins to learn more about their special adaptations.

Penguin Weight
The more that a bird weighs, the larger its wings must be in order to lift itself off the ground. Weighing more also means that a bird must expend greater energy in order to fly the same distance as a smaller bird. There comes a point, when a bird reaches one kilogram in weight, when the size of wings needed to keep the bird in flight makes swimming too difficult. This is the point that ancient penguins arrived at. Penguins weighing one kilogram or more were able to exploit the rich food below the water's surface, and faced with this bountiful food source, penguins evolved heavier bodies and shorter wings to help them catch more food. Flying birds also have their weight concentrated between their wings and around their center of gravity, but in penguins body mass is more evenly distributed.


Penguin Skeleton
A typical bird's skeleton is made of strong, but hollow bones that allow it to fly and float on the water's surface. Therefore, flying birds have a difficult time diving underwater unless they exert considerable energy to overcome their buoyancy. As ancient penguins grew larger and heavier, their bones became solid because they no longer needed hollow flight bones. Penguin skeletons also underwent modification to make them better adapted to swimming than flight.

In other birds, the foot bone (called a tarsometatarsus) is long and slender, but in penguins this bone is short and wide. Penguins also developed very short legs that are pushed toward their backs to allow them to use their feet and tail for steering in the water. This adjustment of the foot and leg bones causes penguins to walk upright, compared to most birds that walk horizontal.

Penguin Waddle
The unusal walking posture in penguins coupled with the fact that their mass is not concentrated around their center of gravity gives them their characteristic "waddle" and often makes them look as if they are in danger of toppling over on land.