Traditionally, bats are divided into two major groups: Megachiroptera or megabats (sometimes called fruit bats or flying foxes) and Microchiroptera or microbats. These names were already a bit misleading, because some ‘megabats’ were small and some ‘microbats’ were big! Families of bats were classified as microbats if they used 'true' echolocation (with calls produced from their larynx or voice box) to navigate or hunt, other families were classified as megabats; it was thought that microbats evolved to echolocate while megabats did not.
But recent research suggests a more complex picture. Studies of genetics have identified different relationships between some families of bats, for example the horseshoe bat family (that are insect eating and tend to be small bats) are genetically more closely related to the families of fruit bats we previously called megabats than they are those families we called microbats. The subdivision of bats into Megachiroptera and Microchiroptera is therefore no longer appropriate. There are two alternative proposals for the new groupings of families of bats: Yinpterochiroptera and Yangochiroptera, and Vespertilioniformes and Pteropodiformes; currently researchers do not all agree which is correct and both sets of names are used.
Some scientists now also believe that echolocation was used by a common ancestor of all the bats that exist in the world today. Echolocation might have then been lost in ‘megabats’, only to re-evolve in some of these species – including greater horseshoe bats and lesser horseshoe bats, which live in the UK.