Complex sentence: Bats have been traditionally thought to be a monophyletic group; according to this model, all living fruit bats and microbats (Microchiroptera) are descendants of a common ancestor species that was already capable of flight.
Split into simpler sentences: Bats have been traditionally thought to be a monophyletic group. According to this model, all living fruit bats and microbats (Microchiroptera) are descendants of a common ancestor species that was already capable of flight.