Horseshoe bats are bats in the family Rhinolophidae. In addition to the single living genus, Rhinolophus, which has about 106 species, the extinct genus Palaeonycteris has been recognized. Horseshoe bats are closely related to the Old World leaf-nosed bats, family Hipposideridae, which have sometimes been included in Rhinolophidae. The horseshoe bats are divided into six subgenera and many species groups. The most recent common ancestor of all horseshoe bats lived 34–40 million years ago, though it is unclear where the geographic roots of the family are, and attempts to determine its biogeography have been indecisive. Their taxonomy is complex, as genetic evidence shows the likely existence of many cryptic species, as well as species recognized as distinct that may have little genetic divergence from previously recognized taxa. They are found in the Old World, mostly in tropical or subtropical areas, including Africa, Asia, Europe, and Oceania.
Horseshoe bats are considered small or medium-sized microbats, weighing , with forearm lengths of and combined lengths of head and body of . The fur, long and smooth in most species, can be reddish-brown, blackish, or bright orange-red. They get their common name from their large nose-leafs, which are shaped like horseshoes. The nose-leafs aid in echolocation; horseshoe bats have highly sophisticated echolocation, using constant frequency calls at high-duty cycles to detect prey in areas of high environmental clutters. They hunt insects and spiders, swooping down on prey from a perch, or gleaning from foliage. Little is known about their mating systems, but at least one species is monogamous, while another is polygynous. Gestation is approximately seven weeks and one offspring is produced at a time. A typical lifespan is six or seven years, but one greater horseshoe bat lived more than thirty years.
Horseshoe bats are relevant to humans in some regions as a source of disease, as food, and for traditional medicine. Several species are the natural reservoirs of various SARS-related coronaviruses, and data strongly suggests they are a reservoir of SARS-CoV, though humans may face more exposure risk from intermediate hosts such as masked palm civets. At first, Rhinolophus was within the family Vespertilionidae. In 1825, British zoologist John Edward Gray subdivided Vespertilionidae into subfamilies, including what he called Rhinolophina. English zoologist Thomas Bell is credited as the first to recognize horseshoe bats as a separate family, using Rhinolophidae in 1836. While Bell is sometimes recognized as the authority for Rhinolophidae, the authority is more often given as Gray, 1825. Horseshoe bats are in the superfamily Rhinolophoidea, along with Craseonycteridae, Hipposideridae Megadermatidae, Rhinonycteridae, and Rhinopomatidae. After the split into Rhinolophidae and Hipposideridae, further divisions were proposed for Rhinolophus, with Rhinolphyllotis in 1934 and Rhinomegalophus in 1951, though both additional genera were returned to Rhinolophus. Various subgenera have been proposed as well, with six listed by Csorba et al. in 2003: Aquias, Phyllorhina, Rhinolophus, Indorhinolophus, Coelophyllus, and Rhinophyllotis. The biogeography of horseshoe bats is poorly understood. Various studies have proposed that the family originated in Europe, Asia, or Africa. A 2010 study supported an Asian or Oriental origin of the family, with rapid evolutionary radiations of the African and Oriental clades during the Oligocene.
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Rhinolophidae is represented by one extant genus, Rhinolophus. Both the family and the genus are confirmed as monophyletic (containing all descendants of a common ancestor). As of 2019, there were 106 described species in Rhinolophus, making it the second-most speciose genus of bat after Myotis. Rhinolophus may be undersampled in the Afrotropical realm, with one genetic study estimating that there could be up to twelve cryptic species in the region. Additionally, some taxa recognized as full species have been found to have little genetic divergence. Rhinolophus kahuzi may be a synonym for the Ruwenzori horseshoe bat (R. ruwenzorii), and R. gorongosae or R. rhodesiae may be synonyms of the Bushveld horseshoe bat (R. simulator). Additionally, Smithers's horseshoe bat (R. smithersi), Cohen's horseshoe bat (R. cohenae), and the Mount Mabu horseshoe bat (R. mabuensis) all have little genetic divergence from Hildebrandt's horseshoe bat (R. hildebrandtii). Recognizing the former three as full species leaves Hildebrandt's horseshoe bat paraphyletic.
The second genus in Rhinolophidae is the extinct Palaeonycteris, with the type species Palaeonycteris robustus. Palaeonycteris robustus lived during the Lower Miocene and its fossilized remains were found in Saint-Gérand-le-Puy, France.
Description
Appearance
thumb|upright|Nose-leaf diagram of a horseshoe bat|alt=A simple outline of the face of a horseshoe bat, facing forward. A large, leaf-like structure is at the center of its face. The pointed tip arising between the eyes is labeled as the lancet; the u-shaped bottom of the nose-leaf is labeled as the horseshoe; the knob projecting outwards from the center of the nose-leaf is the sella
Horseshoe bats are considered small or medium microbats. The majority of species have long, soft fur, but the woolly and lesser woolly horseshoe bats (R. luctus and R. beddomei) are unusual in their very long, woolly fur. In a few horseshoe bat species, males have a false nipple in each armpit. The horseshoe is above the upper lip and is thin and flat. The lancet is triangular, pointed, and pocketed, and points up between the bats' eyes. The sella is a flat, ridge-like structure at the center of the nose. It rises from behind the nostrils and points out perpendicular from the head. This is atypical among bat families, as most newborns have at least some milk teeth at birth, which are quickly replaced by the permanent set.
Postcrania
Several bones in its thorax are fused—the presternum, first rib, partial second rib, seventh cervical vertebra, first thoracic vertebra—making a solid ring. Except for the first digit, which has two phalanges, They echolocate at particularly high frequencies for bats, though not as high as hipposiderids relative to their body sizes, and the majority concentrate most of the echolocation energy into the second harmonic. The king horseshoe bat (R. rex) and the large-eared horseshoe bat (R. philippensis) are examples of outlier species that concentrate energy into the first harmonic rather than the second. Their highly furrowed nose-leafs likely assist in focusing the emission of sound, reducing the effect of environmental clutter. The nose-leaf in general acts like a parabolic reflector, aiming the produced sound while simultaneously shielding the ear from some of it.|alt=Two bat silhouettes. The top, a horseshoe bat, has shorter, broad wings. The second, a free-tailed bat, has very long and narrow wings.]]
Horseshoe bats are insectivorous, though consume other arthropods such as spiders, While a majority of horseshoe bats are nocturnal and hunt at night, Blyth's horseshoe bat (R. lepidus) is known to forage during the daytime on Tioman Island. This is hypothesized as a response to a lack of diurnal avian (day-active bird) predators on the island.
They have especially small and rounded wingtips, low wing loading (meaning they have large wings relative to body mass), and high camber. These factors give them increased agility, and they are capable of making quick, tight turns at slow speeds. Some species, particularly temperate species, have an annual breeding season in the fall, while other species mate in the spring. Gestation takes approximately seven weeks before a single offspring is born, called a pup. Individuals reach sexual maturity by age two. While lifespans typically do not exceed six or seven years, some individuals may have extraordinarily long lives. A greater horseshoe bat individual was once banded and then rediscovered thirty years later. Torpor is employed by horseshoe bats in temperate, sub-tropical, and tropical regions. Hibernation is used by horseshoe bats in temperate regions during the winter months.
Predators and parasites
Overall, bats have few natural predators. Horseshoe bat predators include birds in the order Accipitriformes (hawks, eagles, and kites), as well as falcons and owls. Snakes may also prey on some species while they roost in caves, and domestic cats may hunt them as well. A 2019 study near a colony of bats in central Italy found that 30% of examined cat feces contained the remains of greater horseshoe bats.
Horseshoe bats have a variety of internal and external parasites. External parasites (ectoparasites) include mites in the genus Eyndhovenia, "bat flies" of the families Streblidae and Nycteribiidae, ticks of the genus Ixodes, and fleas of the genus Rhinolophopsylla. They are also affected by a variety of internal parasites (endoparasites), including trematodes of the genera Lecithodendrium, Plagiorchis, Prosthodendrium, and cestodes of the genus Potorolepsis.
Range and habitat
Horseshoe bats have a mostly Paleotropical distribution, though some species are in the southern Palearctic realm. The greater horseshoe bat has the greatest geographic range of any horseshoe bat, occurring across Europe, North Africa, Japan, China, and southern Asia. Other species are much more restricted, like the Andaman horseshoe bat (R. cognatus), which is only found on the Andaman Islands.