At some point in the last 80,000 years, became the “mother” of all sperm whales who followed. Though it would make sense to have a single mother in a single area—an ancestor who, say, really loved the Pacific Ocean—this mom’s genes have been found in sperm whales all over the world.How this happened remains unknown and is even stranger given sperm whales’ social structures. Sperm whales are matrilineal, meaning most females stick together and males come and go, which would limit how far a female’s genes could travel.

Source: Every Sperm Whale Alive Today May Have Descended From the Same Female | Smart News | Smithsonian

And while I’m at it, here’s some more wet mammals: