Livyatan is a mammal confirmed to appear in Additional Creatures: Aquaria.
Livyatan, named after the Leviathan of Hebrew Legend, is a large species of whale that lived in the waters around Peru during the Miocene: 10 million years ago. Livyatan is the largest and most famous of the maco-raptorial sperm whales, a basal group of sperm whales known for their powerful jaws, which they used to tackle large prey. While the size has been debated due to only the skull being discovered, Livyatan is estimated to have been 17 meters in length, making it among the largest apex predatory creatures to have existed. It is also noted for being a potential rival to Megalodon, which it shared its habitat with.
Livyatan in Additional Creatures is planned to be the largest marine mammal in the series, albeit not by length. It plans to have be useful in stand-still combat, forcing its opponents to fight it head-on with high stamina drain. It is also confirmed to be sexually dimorphic.