Megalodons are ancient sea creatures, which were said to go extinct two million years ago. In the episode Strange Migration the Nekton family encountered two megalodons when following an unusual cosmopolitan group of marine animals. The reason all the animals were traveling together far to deep for them to normaly go (due to pressure issues) was that Megalodon had eaten them. And these megalodons ate before mating. They are related to the white sharks, but unlike white sharks, megalodons work together.