The classical view of a monophyletic origin for the Chiroptera states that "Megachiroptera and Microchiroptera are each others closest relatives" (Wible and Novacek, 1988). It has much supporting evidence from biochemical and molecular studies and from morphological characters such as the vascular system of the skull, the post cranial musculoskeletal system, foetal membranes and the nervous system.

However, there is also evidence to support the view that bats are diphyletic. Proponents of a diphyletic origin for the Chiroptera believe that mammals evolved flapping powered flight twice (Pettigrew, 1986). The first event is thought to have taken place in the Cretaceous, when an insectivore type mammal lineage evolved from leaping to full flight in pursuit of flying insects, so giving rise to the Microchiroptera. The second event is thought to have occurred in the Tertiary when an early primate began to glide in search of fruits. Some of these gliders are believed to have evolved into the mammals now referred to as the Megachiroptera (Pettigrew and Jamieson, 1987). The Primate-Megachiropteran link is supported by morphological studies of the penis and nervous system.

The Megachiroptera
(Suborder Megachiroptera) are represented only by the Family Pteropodidae, which are restricted to the Old World tropics of Africa and Asia (Smith, 1977).