Two Great Auks on a Stony Shore
Great Auks are flightless birds in the Ancient Revival Mod. They are extinct, but can be revived if you find their egg. Along with the Great Auk, Ancient Revival has the Thylacine, and Baiji Dolphin. They may look like penguins, but they are closer related to Puffins.
Great Auks do not spawn naturally. They can be revived if the player brushes up a Great Auk Egg from suspicious sand. When the egg is found, it can be placed in a DNA extractor, which can form it's spawn egg. Bringing the great auk back to life will give you the achievement "False Penguin", as the great auk looks like a penguin.