Penguins are birds, not amphibians. They belong to the class Aves, which includes all birds. Penguins are flightless birds that have adapted to life in the water. They have wings that have evolved into flippers, which help them swim efficiently.
Amphibians, on the other hand, belong to the class Amphibia. This class includes animals like frogs, toads, and salamanders. Amphibians typically live both in water and on land during different stages of their life cycle. Unlike penguins, amphibians have moist skin and usually lay their eggs in water.
In summary, penguins are birds because they have feathers, lay hard-shelled eggs, and are warm-blooded. These characteristics are typical of birds and distinguish them from amphibians.