Megabat
Echolocation

Megabats are the only family of bats incapable of laryngeal echolocation. It is unclear whether the common ancestor of all bats was capable of echolocation, and thus echolocation was lost in the megabat lineage, or multiple bat lineages independently evolved the ability to echolocate (the superfamily Rhinolophoidea and the suborder Yangochiroptera). This unknown element of bat evolution has been called a "grand challenge in biology". A 2017 study of bat ontogeny (embryonic development) found evidence that megabat embryos at first have large, developed cochlea similar to echolocating microbats, though at birth they have small cochlea similar to non-echolocating mammals. This evidence supports that laryngeal echolocation evolved once among bats, and was lost in pteropodids, rather than evolving twice independently. Megabats in the genus Rousettus are capable of primitive echolocation through clicking their tongues. Some species — the cave nectar bat (Eonycteris spelaea), lesser short-nosed fruit bat (Cynopterus brachyotis), and the long-tongued fruit bat (Macroglossus sobrinus) — have been shown to create clicks similar to those of echolocating bats using their wings.

Both echolocation and flight are energetically expensive processes. Echolocating bats couple sound production with the mechanisms engaged for flight, allowing them to reduce the additional energy burden of echolocation. Instead of pressurizing a bolus of air for the production of sound, laryngeally echolocating bats likely use the force of the downbeat of their wings to pressurize the air, cutting energetic costs by synchronizing wingbeats and echolocation. The loss of echolocation (or conversely, the lack of its evolution) may be due to the uncoupling of flight and echolocation in megabats. The larger average body size of megabats compared to echolocating bats suggests a larger body size disrupts the flight-echolocation coupling and made echolocation too energetically expensive to be conserved in megabats.
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