Hyana

Scientific classification

• Kingdom: Animalia
• Phylum: Chordata
• Class: Mammalia
• Order: Carnivora
• Suborder: Feliformia
• Family: Hyaenidae:  Gray, 1821

Subfamilies and Genera

• Hyaeninae
  • Crocuta
  • Hyaena
  • Parahyaena
• Protelinae
  • Proteles

Physiology

Although hyenas bear some physical resemblance to canids, they make up a separate biological family that is most closely related to Herpestidae (the family of mongooses and meerkats), though not all scientists agree. With the exception of the insectivorous Aardwolf, hyenas have among the strongest jaws in the animal kingdom and an adult of the species has only the big cats (e.g. lions or leopards) to fear.

All species have a distinctly bear-like gait due to their front legs being longer than their back legs. The Aardwolf, striped hyena and brown hyena have luxurious, striped pelts and manes lining the top of their necks which erect when frightened. The spotted hyena's fur is considerably shorter and is spotted rather than striped. Unlike other species, its mane is reversed forwards.

Hyenas are highly intelligent animals, and some scientists claim they are of equal intelligence to certain apes. One indication of hyena intelligence is that they will move their kills closer to each other to protect them from scavengers; another indication is their strategic hunting methods.

The majority of hyena species show little sexual dimorphism, usually with males being only slightly larger than the females. The spotted hyena is an exception to this as females are larger than the males and dominate them. One unusual feature of the spotted hyena is that females have an enlarged clitoris called a pseudo-penis, demi-penis, or sometimes mistakenly referred to as a nanophallus. Female hyenas give birth, copulate, and urinate through their protruding genitalia, which stretches to allow the male penis to enter for copulation, and it also stretches during birth. The anatomical position of the genitalia gives females total sexual control over who is allowed to mate with them. Researchers originally thought that one cause of this characteristic of the genitals was androgens that were introduced to the fetus very early on in its development. However, it was discovered that when the androgens were held back from the fetus, the development of the female genitalia was not altered.

All species excrete an oily, yellow substance from their anal glands onto objects to mark their territories. When scent marking, the anal pouch is turned inside out, or inverted. Hyenas also do this as a submissive posture to more dominant hyenas. Genitals, the anal area, and the anal glands are sniffed during greeting ceremonies in which each hyena lifts its leg and allows the other to sniff its anal sacks and genitals. All four species maintain latrines far from the main den area where dung is deposited. Scent marking is also done by scraping the ground with the paws, which deposits scent from glands on the bottoms of the feet.

Reproduction
The female Spotted Hyena's urogenital system is unique among mammals: the clitoris is elongated to form a fully erectile phallus, the vaginal opening is at the tip of this phallus. - only the shape of the glans at the tip of the phallus makes it possible to differentiate the sexes. The female urinates, mates and gives birth through this pseudo-penis. Since it is impossible to penetrate without the female's cooperation, female hyena have full control over whom they choose to mate with. The male hyena's penis lacks a baculum, a bone found in the genitals of most mammals.

Birth is very difficult: the internal birth canal extends almost to the subcaudal location of the vulva (which in Crocuta is fused to form a scrotum containing fatty pseudo-testes) before turning abruptly towards the clitoris, and the clitoris itself is narrow (although it ruptures with the first parturition, making subsequent births easier). In captivity, many cubs of primiparous mothers are stillborn because of the long labor times involved, and in the wild, it is estimated that 10% of first time mothers die during labor. These factors suggests that at some point there must have been powerful selective pressures driving the evolution of masculinisation.

Researchers originally thought that one of the things that causes this characteristic of the genitals is androgens that are expressed to the fetus very early on in its development. However, it was discovered that when the androgens are held back from the fetus, the development of the female genitalia was not altered. Other hyena species lack this adaptation, making it a fairly recent one in the hyena line. Masculinised female genitalia also appears in some lemurs, spider monkeys, and the Binturong but the fused vulva is unique to the hyena.

Hyenas are born with their eyes open and teeth already fully developed after a 4 month gestation period. At birth, the cubs weigh 2.2 to 3.6 lb (1-1.6 kg), and are among the few mammals to commit neonatal siblicide. A same sexed litter will result in vicious fighting between the cubs, often resulting in death. This siblicide is estimated to contribute to 25% of hyena cub mortality. Since a single cub will receive more food and mature faster, this behavior is probably adaptive. Spotted hyena milk is very rich, having the highest protein content (14.9%) of any terrestrial carnivore, and the fat content (14.1%) is second only to the polar bear, so unlike lions and wild dogs, they can leave their cubs for about a week without feeding them. Two to six weeks after whelping, young are transported to the communal den. Young depend entirely on milk for about 8 months and are not weaned until 12 to 16 months old. Maturation is at three years, females later than males. Female offspring remain in their natal clan while males l