<Li> They were specialized nectar - feeders that evolved to feed on another type of liquid </Li> <P> The vampire bat lineage diverged from its family 26 million years ago . The hairy - legged vampire bat likely diverged from the other two species of vampire bats 21.7 million years ago . Because the hairy - legged vampire bat feeds on bird blood and it is the ancestral vampire bat, it is likely that all vampire bats initially fed on bird blood . Recent analyses suggest that vampire bats arose from insectivores, which discount the frugivore, carnivore, and nectarivore hypotheses of origin . Within 4 million years of diverging from other Phyllostomids, vampire bats had evolved all necessary adaptations for blood - feeding, making it one of the fastest examples of natural selection among mammals . </P> <P> Unlike fruit bats, the vampire bats have short, conical muzzles . It also lacks a nose leaf, instead having naked pads with U-shaped grooves at the tip . The common vampire bat, Desmodus rotundus, also has specialized thermoreceptors on its nose, which aid the animal in locating areas where the blood flows close to the skin of its prey . A nucleus has been found in the brain of vampire bats that has a similar position and similar histology to the infrared receptor of infrared - sensing snakes . </P> <P> A vampire bat has front teeth that are specialized for cutting and the back teeth are much smaller than in other bats . The inferior colliculus, the part of the bat's brain that processes sound, is well adapted to detecting the regular breathing sounds of sleeping animals that serve as its main food source . </P>

Four types of animals in which vampire species can be found