The Relic (1997)

A detective is puzzled after recent spate of deaths involving decapitations. He visits a museum when a new victim is found murdered in the same way. In the museum, he encounters an evolutionary biologist who herself is puzzled after discovering a mutated beetle that possesses both insect and reptilian DNA. The detective finds a common link between the murders, hypothalamus missing from the brains of the victims. Together they both try to defeat a monster/killer who is on a killing spree.