They use only their hindlimbs to walk, which is called bipedalism; their forelimbs have evolved to become wings.
Their forelimbs have evolved to become wings. They use only their hindlimbs to walk, which is called bipedalism.
They use only their hindlimbs to walk, which is called bipedalism. Their forelimbs have evolved to become wings.
They use only their hindlimbs to walk, which is called bipedalism. Their forelimbs have evolved to become wings.