Dinoshark (movie, 2010)

The film opens with a baby dinoshark swimming away from a broken chunk of Arctic glacier that calved due to global warming. Three years later, the dinoshark is a ferocious predatory adult and kills tourists and locals offshore from Puerto Vallarta, Mexico. The protagonist, Trace, is first to notice the Dinoshark and witnesses his friend get eaten, but has trouble convincing people that a creature of such antiquity is still alive and eating people.