Physical Appearance
Hyenas are members of the family hyaenidae, the order carnivora. They are rather doglike in appearance, but are actually more closely related to cats and viverridae (civets, mongooses, genets) than they are to dogs. They share many things in common with the civet family, to which they share the closest relation. One is that both hyenas and civets posess highly developed anal glands that are used for marking territory and for olfactory (scent) communication. The aardwolf is the closest to the civets because it eats mostly insects.
Hyenas in general are medium to large sized animals, with both sexes being similair in size, with the exception of the spotted hyena. They have exceptionally powerful jaw muscles. They have 32-34 teeth; in combination with their powerful jaws they can crack bone. The ears are relatively large in comparision to body size, and can be round or pointed. Their long sloping hindquarters are very muscular. Their genitals have no baculum (a bone commonly found in the penis of carnivores), and the base of the penis is covered with small, backwards facing spines, similar to the cat family. These spines are used to stimulate ovulation. With the exeption of the spotted hyena (Crocuta crocuta), the females have normal genetalia.
Hyenas have a very large digestive system that makes quick work of even bones and teeth in a couple of hours. Hyenas, unlike any other carnivore, can utilise all the carcass for energy. It is believed that the reason hyenas nurse their young for more than a year is because of the high proportion of bone in their diet.
History and Evolution of the Hyena
Hyenas are the latest addition to the order of carnivora. They arose in the Miocece, some ten million years ago, from civet-like creatures in Eurasia. The single species that would lay the groung for modern hyenas split into two groups around the early Pliocene, into the spotted (Crocuta sp.) and striped (Hyaena sp.) types. The hyenas success was primarily because other predators, such as the sabre tooth tiger, could not make the full use of the carcasses. Hyenas regularly traveled between Africa and Eurasia, but now only exist in Africa, probably due to climactic changes. There were more species of hyenas than there are now. The hyenas peak was reached in the Pleistocene, with 4 genera and 9 species of hyena; of these only the three genera and four species survived. In Eurasia, the genera Crocuta diversified into many species before it became extinct. Despite the lack of fossil evidence, the aardwolf (Proteles cristatus) is believed, because of its appearance, anatomy and behavior, to be decended from the Hyaena line. It was believed to be a striped hyena (Hyaena hyaena) modified into a insectivore.
Social Behavior
It was long thought that the spotted hyena was the only member of the family Hyaenidae that was social and was gregarious (lives in groups). It is now known that this is not the case. The two species of the genera Hyaena, the striped and brown hyenas, were found to be gregarious as well. The only true solitary hyena is the aardwolf. In all three gregarious species, they are solitary foragers, but live in large family groups. The hyenas seem to have a territorial defense against members of the same sex, but allow members of the opposite sex to roam freely in their territory. Hyenas are primarily nocturnal, but the spotted hyena is active during the daytime as well.
Communication
Olfactory:
All species participate in "pasting", which is when they excrete an oily, yellow substance from their anal glands onto surrounding bushes and grass. To do this, the anal pouch is turned inside out, or everted. They do this to mark their territory. Hyenas also evert their anal glands as a submissive posture to dominant hyenas. Genitals, the anal area, and the anal glands are sniffed during a greeting ceremony. Each hyena lifts its leg and allows the other to sniff its anal sacks and genitals. The greeting ceremony can last for up to ten minutes. All four species maintain latrines where feces is deposited. It is unknown why they do this, but it is thought to be for sanitary purposes, because the latrine is as far as possible from the denning area. Scent marking is also done by scraping the ground with the paws, which deposits scent from glands on the bottoms of the feet.
Vocal:
Hyenas' vocalizations consist of whining, giggling, growling, and grumbling. Most hyenas' calls are softer than the spotted hyenas' calls, and are only spoken during contact with members of their own family. The cubs whine for food, they giggle when chased after while carrying food, and growling while play-fighting. They have a rare long-distance call, like a cackle, that is not often used. They also use a kind of cooing sound when interacting with one another affectionately. Spotted hyenas are famous for their whooping calls and their "laugh". Their whooping call is a warning call, and they "laugh" when they are scared.
Visual:
Hyenas have numerous visual displays used to indicate their mood and rank within the loosely established social heirarchy. They have dominance and submission displays. Dominant displays include bristling, erecting tail and ears, hunching back and growling. Submission postures include presenting anal glands, flattening ears, a "fear grimace" which looks like a smile in loose human terms, and licking lips. When they fight, the usually bite the neck and rump areas, along with muzzle wrestling, in which one hyena grabs the others' lower jaw. When fighting, they must protect their hind legs, and do so by dropping their hindquarters to the ground.
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