Evidence for echolocation in the oldest known bats

The earliest-known bats are represented by excellent fossil material, including virtually complete skeletons of Icaronycteris index from the early Eocene (50 Myr BP) of western Wyoming1,2 and Palaeochiropteryx tupaiodon from the middle Eocene (45 Myr BP) ‘Grube Messel’ of western Germany3,4. These taxa have been closely allied1,5 with Recent Microchiroptera, a suborder of diverse bats noted for their powers of ultrasonic echolocation6. A problem with this relationship is the alleged absence in the Eocene forms of specializations in the auditory region7 and other aspects of the skeletal system1,2. It has been proposed, therefore, that the oldest bats are members of a group more primitive and possibly ancestral to the Microchiroptera and the visually oriented Megachiroptera8. Previously undescribed specimens now show, however, that Icaronycteris (Fig. 1) and Palaeochiropteryx (Fig. 2) share special basicranial features with microchiropterans which suggest comparable refinement of ultrasonic echolocation. These results support the theory that a sophisticated sonar system was present in the earliest records of microchiropteran history