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The family Hyaenidae includes just four extant species, each placed in its own genus: the Brown Hyena (Parahyaena brunnea), the Striped Hyena (Hyaena hyaena), the Spotted (or Laughing) Hyena (Crocuta crocuta), and the Aardwolf (Proteles cristata) (the Aardwolf was at one time placed in its own family, the Protelidae). The three hyenas are grouped together in the subfamily Hyaeninae ("bone-cracking hyenas"), with the Brown Hyena and Striped Hyena as sister taxa (Koepfli et al. 2006; Agnarsson et al. 2010), whereas the Aardwolf is placed by itself as the sole extant species in the subfamily Protelinae. Hyaenids are fairly large carnivores, ranging from around 10 to 80 kilograms. They have bushy tails and all but the Brown Hyena have striped or spotted coats. The forelegs are longer than the hindlegs, giving the back a sloped appearance. Unlike other carnivores, male hyaenids lack a baculum (a "penis bone", present in many mammals, but not, among others, in humans). Spotted Hyenas are well known for the masculinized genitalia of females. Female Spotted Hyenas have no external vagina, so urination, insertion of the male's penis during copulation, and birth all take place through the clitoris, which is fully erectile and closely resembles the male's penis.

The bone-cracking hyenas have large skulls with powerful jaws and large premolar teeth that are used to break open bones to access the marrow within. The bite force of a bone-cracking hyena is five to ten times that of a similar-sized domestic dog. In contrast, the skull of the Aardwolf--which feeds almost exclusively on Trinervitermes harvester termites that produce noxious terpene defensive compounds which protect them from most other potential predators (Richardson and Levitan 1994)--is far more delicate and only the canines (used for fighting) are large and sharp.

Modern hyaenids are found from Africa and the Middle East to India and Nepal across a range of habitat types including deserts, thick bush, swamps, montane forests, and open savannas. Hyaenids are generally nocturnal, although some are commonly active around dawn and dusk and Spotted Hyenas in many areas are often active on cool or rainy days. Social structure varies greatly among the four species. Aardwolves generally form monogamous pairs for breeding (although they are known to mate with individuals other than their partners as well), but are otherwise solitary. Brown Hyenas live in small family groups. Spotted Hyenas live in large, complex societies that more closely resemble those of Old World monkeys than those of any other carnivore species (Watts and Holekamp 2007). Spotted Hyenas bring their young several weeks after birth to a communal den, which may contain up to 30 young of different ages from up to 20 litters, but females generally nurse only their own young. The social lives of Striped Hyenas have not been well studies, but it appears that in different areas they may range from solitary to forming small polyandrous groups (i.e., with one female and multiple males) to forming small family groups like those of the Brown Hyena. Spotted Hyena cubs are born with their eyes open and canine and deciduous teeth emerged; Brown and Striped Hyenas are born with their eyes closed and are generally less precocial than Spotted Hyenas.

Aardwolves are strictly insectivorous, licking termites from the soil surface using their broad, sticky tongues; a single Aardwolf may consume hundreds of thousands of termites in a night. Striped and Brown Hyenas feed mainly on carrion and Spotted Hyenas feed mainly on medium- and large-sized antelopes that they kill themselves. Except for Spotted Hyenas, which may hunt alone or in large groups, hyaenids are strictly solitary foragers.

Aardwolves are found in two disjunct areas, in East Africa and southern Africa, separated by around 1500 km, and live mainly in open, grassy plains or in bush country, although they can be found in a range of habitats with annual rainfall of 100-600 mm (they are absent from forests and deserts).  Spotted Hyenas are found over most of Africa south of the Sahara Desert, including savanna, bushveld, desert, swamps, woodland, and montane forest up to 4000 m elevation (they are absent from lowland tropical rainforests), but have been extirpated from many areas in southern Africa. Striped Hyenas have a large (but patchy and low density) distribution around the perimeter of the northern half of the continent of Africa (i.e., excluding the central Sahara Desert) and in the Middle East and Central Asia. Across most of their range, Striped Hyenas are found in rugged, arid habitats or light thorn bush country, but they occur also in grasslands, open woodlands, and mountainous areas; they drink regularly where water is available, but can survive in waterless areas as well. Brown Hyenas are distributed across much of southern Africa south of Angola in a range of relatively arid habitats such as open woodland savanna and bushveld; they do not require drinking water and can live in areas with less than 100 mm annual rainfall, such as extreme desert habitat along the southwestern coast of Africa.

Habitat loss poses a serious threat to all four hyaenids, although other threats such as cars and other intentional and unintentional killing by humans are also very significant.

(Holekamp and Kolowski 2009 and references therein)

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