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.
They are hunted for food in several regions, particularly sub-Saharan Africa, but also Southeast Asia. Some species or their guano are used in traditional medicine in Nepal, India, Vietnam, and Senegal.
Taxonomy and evolution Taxonomic history
Rhinolophus was first described as a genus in 1799 by French naturalist Bernard Germain de Lacépède. Initially, all extant horseshoe bats were in Rhinolophus, as well as the species now in Hipposideros (roundleaf bats). 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.
Attempts were made to divide Rhinolophus into other genera. In 1816, English zoologist William Elford Leach proposed the genus name Phyllorhina; Gray proposed Aquias in 1847 and Phyllotis in 1866; and German naturalist Wilhelm Peters proposed Coelophyllus in 1867. In 1876, Irish zoologist George Edward Dobson returned all Asiatic horseshoe bats to Rhinolophus, additionally proposing the subfamilies Phyllorhininae (for the hipposiderids) and Rhinolophinae. American zoologist Gerrit Smith Miller Jr. further divided the hipposiderids from the horseshoe bats in 1907, recognizing Hipposideridae as a distinct family. Some authors have considered Hipposideros and associated genera as part of Rhinolophidae as recently as the early 2000s, though they are now most often recognized as a separate family. 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.
Danish mammalogist Knud Andersen was the first to propose species groups for Rhinolophus, doing so in 1905. Species groups are a way of clustering species to reflect evolutionary relationships. He recognized six species groups: R. simplex (now R. megaphyllus), R. lepidus, R. midas (now R. hipposideros), R. philippinensis, R. macrotis, and R. arcuatus. The species have been frequently rearranged among the groups as new groups are added, new species are described, and relationships among species are revised. Fifteen species groups were given by Csorba and colleagues in 2003. Various subgenera have been proposed as well, with six listed by Csorba et al. in 2003: Aquias, Phyllorhina, Rhinolophus, Indorhinolophus, Coelophyllus, and Rhinophyllotis. Informally, the rhinolophids can be split into two major clades: the mostly African clade, and the mostly Oriental clade.
Evolutionary history
The most recent common ancestor of Rhinolophus lived an estimated 34–40 million years ago, splitting from the hipposiderid lineage during the Eocene. Fossilized horseshoe bats are known from Europe (early to mid-Miocene, early Oligocene), Australia (Miocene), and Africa (Miocene and late Pliocene). 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. A 2019 study found that R. xinanzhongguoensis and R. nippon, both Eurasian species, are more closely related to African species than to other Eurasian species, suggesting that rhinolophids may have a complex biogeographical relationship with Asia and the Afrotropics.
A 2016 study using mitochondrial and nuclear DNA placed the horseshoe bats within the Yinpterochiroptera as sister to Hipposideridae.
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
Horseshoe bats are considered small or medium microbats. Individuals have a head and body length ranging and have forearm lengths of . One of the smaller species, the lesser horseshoe bat (R. hipposideros), weighs , while one of the larger species, the greater horseshoe bat (R. ferrumequinum), weighs . Fur color is highly variable among species, ranging from blackish to reddish brown to bright orange-red. The underparts are paler than the back fur. 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.
Like most bats, horseshoe bats have two mammary glands on their chests. Adult females additionally have two teat-like projections on their abdomens, called pubic nipples or false nipples, which are not connected to mammary glands. Only a few other bat families have pubic nipples, including Hipposideridae, Craseonycteridae, Megadermatidae, and Rhinopomatidae; they serve as attachment points for their offspring. In a few horseshoe bat species, males have a false nipple in each armpit.
Head and teeth
All horseshoe bats have large, leaf-like protuberances on their noses, which are called nose-leafs. The nose-leafs are important in species identification, and are composed of several parts. The front of the nose-leaf resembles and is called a horseshoe, earning them the common name of "horseshoe bats". 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. Their ears are large and leaf-shaped, nearly as broad as they are long, and lack tragi. The antitragi of the ears are conspicuous. Their eyes are very small. The skull always has a rostral inflation, or bony protrusion on the snout. The typical dental formula of a horseshoe bat is , but the middle lower premolars are often missing, as well as the anterior upper premolars (premolars towards the front of the mouth). The young lose their milk teeth while still in utero, with the teeth resorbed into the body. They are born with the four permanent canine teeth erupted, which enables them to cling to their mothers. 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. This fusion is associated with the ability to echolocate while stationary. Except for the first digit, which has two phalanges, all of their toes have three phalanges. This distinguishes them from hipposiderids, which have two phalanges in all toes. The tail is completely enclosed in the uropatagium (tail membrane), and the trailing edge of the uropatagium has calcars (cartilaginous spurs).
Biology and ecology Echolocation and hearing