Xiphactinus closeup
Xiphactinus is a predatory fish that lived most of the late Cretaeous.  It ate smaller fish and baby marine reptiles.  It is not related to the shark because it did not have a cartolatches skin but scales like a modern day fish.  This predator may have acted more like modern day Baracudas, they would live in schools and swarm there prey.  They lived up and down the Western Interior Sea.