Noseleaves are complex fleshy structures that are present on the nose of many echolocating bats, especially within families such as Phyllostomidae, Hipposideridae, and Rhinolophidae. Noseleaves are very important in molding and controlling echolocation calls used for nasal echolocation in bats.
Besides playing this fundamental role in echolocation, noseleaves are very diverse and complex and often differ among different bat species based on variations in foraging habits and sensory specializations. The diversity of noseleaves is closely related to their echolocation role and to their evolution, including multiple independent origins and examples of convergent evolution. Noseleaves are important for linking echolocation and ecology and for gaining insight into how morphological specializations can influence behavioral and evolutionary patterns in bats.
Noseleaves are found in three families: all members of family Phyllostomidae (also known as the leaf-nosed bats), as well as certain members of Hipposideridae and Rhinolophidae. Echolocation is the ancestral condition of all extant bats, but has been lost in Pteropodidae. Most living echolocating bats are nasal emissors. This transition in bat evolution created a selective pressure to direct the sound beam and focus the emission. Noseleaves are an adaptation for nasal echolocation, and serve multiple purposes: to filter for interference before the sound gets to the receptor organ, provide directionality, and enhance prey detection.
The noseleaf has several independent evolutionary origins. Rhinolophidae and Hipposideridae noseleafs tend to have similar patterns, evolved in the Old World. While Phyllostomidae have a complete different one, evolved independently in the New World.
The noseleaf helps to modify and direct the sound beam during echolocation. Modeling experiments suggest that these modifications can influence the width, frequency, and direction of the sound beam. These structures work together to enhance the directional echolocation calls of the animal and reflect signals back from the nose to the pinnae (ears). The general structure of a noseleaf is a concave dish with a series of protrusions that amplifies and directs pulses from the nostrils.
In phyllostomid and horseshoe bats, the nose is divided into the three main parts. Above the nostrils, the nose reaches a point known as the spear or lancet. The lancet is responsible for directing pulses along a vertical axis. Horseshoe bats are known to quickly flick their lancet to redirect sound beams. The section protruding most distally from the face is called the sella. The furrow beneath the nostrils is the anterior leaf, or "horseshoe". Hipposterid bats lack the lancet at the tip of the nose. Although these families contain functionally similar structures, their arrangement on the face differs broadly.
Several patterns tend to be followed by the families with prominent noseleaves, despite independent evolution of the structure. These structures vary in shape and size across different bat species, and are often used as anatomical landmarks to resolve phylogenetic relationships between species.
Studies have indicated that the functional role of the noseleaf could potentially differ depending on the level of sensory specializations of the echolocating species of bats. Other studies have indicated that the spatial relationship of the noseleaf with the pinnae could play an integral role in the echolocation signal emission of the hipposiderid bats.
Morphological variation in noseleaves has been associated with echolocation strategy, habitat, and foraging behavior among nasal echolocators. For instance, variation in size, shape, and complexity of noseleaves may influence echolocation calls, thereby affecting prey detection and localization in different ecological contexts.
Comparative studies among bat families indicate that echolocation signal directionality, sensitivity, and ecological constraints are often associated with specialization in noseleaf shape.