Mosasaurus (meaning "lizard of the Meuse River") is a genus of mosasaur, carnivorous, aquatic lizards, somewhat resembling flippered crocodiles, with elongated heavy jaws. The name means "Meuse lizard", as the first specimen was found near the Meuse River (Latin Mosa + Greek sauros (lizard)). Since they are aquatic animals, their eggs need to be placed in water.
Mosasaurus in this mod resembles the real-life Mosasaurus. It has a dark green body, a beige underbelly, a crocodile-like head, a beige tail-fin and red eyes. The egg must be placed in the water in order for it to hatch. It is one of two fully aquatic reptiles along with Liopleurodon. When it is fully grown (20 Minecraft days), it will be 14 blocks in length. It can be very dangerous at times of being attacked or not being attacked. It can take 24 hits of a baby Mosasaurus to kill you with full armor.
Mosasaurus can't be tamed. They will attack certain creatures, including cows, players, plesiosaurs, nautili and coelacanths that are unfortunate enough to swim near their territories. Mosasaurus can't be hand-fed like any other dinosaur in this mod—you need to put a living Nautilus, squid, or Coelacanth in the water and it will eat it. Mosasaurus are able to fish for themselves, but they can't eat fish that they catch. This could be used to build a PvP moat, although you must try not to fall in. Do not use fences for their enclosure. They will die if they come in contact with fences. When they come in contact with fences, they will take a 4 block fall and be damaged. Their habitat needs to be submerged in water. They eat from feeders which makes them self-reliant.