Mawsonia are fish confirmed to appear in Additional Creatures: Aquaria.
Mawsonia, named after Mawson who was one of the people to discover it, is a giant species of coelacanth that lived throughout North Africa and Brazil during the Cretaceous: 115-95 million years ago. Mawsonia stands out primarily for its large size. At 6 meters long, it is the largest coelacanth known to exist, as well as one of the largest freshwater fish known, period. At this massive size, Mawsonia likely had very few predators when fully grown, save for the occasional spinosaur.
Mawsonia in Additional Creatures is planned to be a large and formidable creature. Mawsonia will have the ability to swallow players whole, instantly killing them and keeping the items the player has within their bodies, forcing the player to kill it in order to get the items back. This also applies to similar-sized smaller creatures. After swallowing any particular prey item, Mawsonia will gain a buff to health regeneration and food for a duration. During this duration, it is also unable to swallow anything else whole.