The Xiphactinus was a ray-finned fish that lived in the late cretaceous. It had monster size, teeth, and strength. The Xiphactinus is a close cousin of today's swordfish, mackerel, and marlin. In fed on large and small fish, octopi, squid, and several other prey it could fit in its large mouth. Xiphactinus became extinct not long before the end of the Cretaceous period.
In Zoo Tycoon 2
Xiphactinus is an animal that features in the cancelled user-expansion pack Zoo Tycoon 2: Formidable Seas.