Here is a list of a few gigantic ancient animals that once roamed the Earth. The first ancient animal to be listed is the Permian arthropod, the largest insect known to be capable of flight. The second animal is a deinosuchus, a form of an ancient crocodile considered a family member of modern day alligators. The third is Archelon, which is a giant sea turtle looking species with more than 10 feet long from nose to tail. Fourth is Megalodon, the largest shark known to have ever lived. Fifth is Titanoba, which is an accent snake that was roughly 43 feet long. Lastly, are Terror Birds that went into extinct about 2.5 million years ago.