What flying mammal is thought to be related to vampires?

This nocturnal, flying mammal feeds exclusively on the blood of other animals. To eat the blood, the vampire bat is equipped with sharp incisor teeth that are used to nip a small piece of flesh. An anticoagulant in the vampire bat's saliva allows the blood to flow continually instead of clotting. The bat then laps the blood that flows from the wound with its grooved tongue.

Source: Zoo America