Complex sentence: Alcids are superficially similar to penguins due to their black-and-white colours, their upright posture and some of their habits, however they are not related to the penguins and differ in being able to fly.
Split into simpler sentences: Alcids are superficially similar to penguins due to their black-and-white colours, their upright posture and some of their habits. However, they are not related to the penguins and differ in being able to fly.