* The Penguins themselves! The penguin lineage has seen many species come and go throughout history. Some of these extinct penguin species were quite different from modern penguins, with some being much larger. For example, the giant penguin (_Palaeeudyptes klekowskii_) stood over 5 feet tall!
* The Giant Moa:** While not directly related to penguins, these extinct birds from New Zealand were flightless and had a similar upright stance. They were quite large, with some species reaching up to 10 feet tall.
* The Dodo:** Another flightless bird, the dodo from Mauritius, was also similar in appearance to penguins in its upright posture and short wings. The dodo, unfortunately, went extinct in the 17th century due to human activity.
* The Elephant Birds: These giant flightless birds from Madagascar went extinct relatively recently, around 1,000 years ago. They were even larger than the moa, reaching up to 10 feet tall.
It's important to remember that these animals are just examples and the relationships between penguins and other flightless birds are complex and still being studied.