* They lay eggs: Mammals give birth to live young, but penguins, like birds, reproduce by laying eggs.
* They have feathers: Mammals have hair or fur for insulation, while penguins have feathers, which are unique to birds.
* They have wings: Penguins have modified wings that function as flippers for swimming, while mammals do not have wings.
* They have a beak: Penguins have beaks for catching and eating fish, while mammals have mouths with teeth.
* They are warm-blooded: While both mammals and birds are warm-blooded, they achieve this through different mechanisms. Mammals regulate their body temperature with fur and sweat glands, while birds use feathers and their respiratory system.
Penguins are classified as birds within the order Sphenisciformes. They share a common ancestor with other birds, but they have evolved unique adaptations for their aquatic lifestyle.