The largest animal on Thanatos, the tusked leviathan is a 250 foot long, 180 ton predator.
Tusked leviathans resemble the extinct shark Hybodus from Earth, but as it's name suggests, it has 4 tusks. 2 come out from the lower jaw, the other 2 from the upper jaw. Around it's face, there are cephalopod like tentacles. The tusks are 15 feet long on the lower jaws, and 30 feet on the uppers. The tusks are serrated as well. It has only 1 dorsal fin, and has 8 gill slits. The dorsal fin is 25 feet tall, and the pectorals are 30 feet long. It's tail fin is only 15 foot tall. And it's non tusk teeth are 70 centimeters long.
Tusked leviathans eat everything else in their habitat. They have no predators at all.