Tylosaurus is a genus of mosasaur (an oceanic-lizard) from North America during the late-cretaceous period, around eighty-one-million-years ago.
Tylosaurus and all mosasaurs in general are related to monitor-lizards. They also have a second set of teeth in the palate, plus a dorsal-crest. It was also one of the biggest of mosasaurs.
A Tylosaurus was seen Pero Pero's flashback trying to attack Heart, only to be killed.