Gigantism seems like a past phenomenon, given that enormous animals such as Megalodon and Tyrannosaurus rex died out millions of years ago. The largest vertebrate that has ever lived, however, is part of the present, and not past, animal kingdom. The distinction goes to the blue whale, which can reach lengths of over 100 feet. The oldest members of the baleen-whale lineage appeared about 36 million years ago, yet new research finds that very large members of this lineage only appear at around 2–3 million years ago, which is a drop in the evolutionary bucket.
https://www.seeker.com/earth/animals/whales-only-recently-evolved-into-giants
