Phylogeny – The evolutionary history behind the development of a trait

The fossil record of bats extends over 50 million years, and the early evolution of bats still remains unclear [10]. Bats are the only mammals able to truly fly [13]. It isn't known whether the ancestors of bats were nocturnal, diurnal, or crepuscular, which would affect whether they could echolocate or not. Early bats would have to have improved orientation skills to be successful night fliers. The night was a niche full of insects with hardly any predators, and early bats could have access to this plentiful food source as echolocation evolved. It is heavily debated whether echolocation evolved after flight, before flight, or alongside flight. Most likely, echolocation evolved after or alongside flight. An Eocene bat described by Simmons et al. is capable of flight, but likely not capable of echolocation. Echolocation is very beneficial, with little energy loss, when coupled with flight, whereas stationary echolocation is very energetically costly to the individual [1, 13].

Currently, there are over 800 species of echolocating bats, and all are under the suborder Microchiroptera. Microbat families in the superfamily Rhinolophoidea, however, may be more closely related to the megabats than they are to microbats. This implies that echolocation systems either have evolved independently in rhinolophoids and in other microbats, or were lost in the evolution in megabats [13]. Echolocation could have been lost due to changes in foraging behavior or habitat. Or perhaps echolocation could have been selected against in favor of visual acuity and a larger body size, which would have been impossible if, as suggested, echolocation systems limit body size in bats [13]. Springer et al.'s results from their integrated fossil and molecular data of Eocene bats suggest that laryngeal echolocation was possessed by a common ancestor and subsequently lost in megabats and rhinolophoids[11]. They suggest that the last shared ancestor was 52-54 million years ago [11].fig3

Figure 2. A picture showing the external features of three microbat species today, especially the ears and noses (Gareth Jones 2005)

 

 

 

 

Although echolocation likely evolved only once in Chiroptera, there have been numerous modifications in Microchiroptera since. Echolocation likely began as a primitive type of cycle echolocation used for orientation and obstacle detection [11]. Mircobats have evolved very similar features assisting with echolocation. The ears, noses, and larynxes have all evolved in different microbats, providing a huge range of these features today. Ears tend to be complex, with large pinnae, many bats have noseleaves to direct outgoing sounds, and larynxes tend to be elongated. Figure 2. A picture showing the external features of three microbat species today, especially the ears and noses (Gareth Jones 2005)