Hyracoidea

Hyraxes (), also called dassies, are small, stout, thickset, herbivorous mammals in the family Procaviidae within the order Hyracoidea. Hyraxes are well-furred, rotund animals with short tails. Modern hyraxes are typically between in length and weigh between . They are superficially similar to marmots or over-large pikas but are much more closely related to elephants and sirenians. Hyraxes have a life span of 9 to 14 years. Both types of "rock" hyrax ( ''P. capensis'' and ''H. brucei'') live on rock outcrops, including cliffs in Ethiopia and isolated granite outcrops called koppies in southern Africa.

Almost all hyraxes are limited to Africa; the exception is the rock hyrax (''P. capensis'') which is also found in adjacent parts of the Middle East.

Hyraxes were a much more diverse group in the past encompassing species considerably larger than modern hyraxes. The largest known extinct hyrax, '' Titanohyrax ultimus'', has been estimated to weigh , comparable to a rhinoceros.

Characteristics

Hyraxes retain or have redeveloped a number of primitive mammalian characteristics; in particular, they have poorly developed internal temperature regulation,
for which they compensate by behavioural thermoregulation, such as huddling together and basking in the sun.

Unlike most other browsing and grazing animals, they do not use the incisors at the front of the jaw for slicing off leaves and grass; rather, they use the molar teeth at the side of the jaw. The two upper incisors are large and tusk-like, and grow continuously through life, similar to those of rodents. The four lower incisors are deeply grooved "comb teeth". A diastema occurs between the incisors and the cheek teeth. The permanent dental formula for hyraxes is although sometimes stated as because the deciduous canine teeth are occasionally retained into early adulthood.

Although not ruminants, hyraxes have complex, multichambered stomachs that allow symbiotic bacteria to break down tough plant materials, but their overall ability to digest fibre is lower than that of the ungulates.
Their mandibular motions are similar to chewing cud,

but the hyrax is physically incapable of regurgitation
as in the even-toed ungulates and some of the macropods. This chewing behaviour may be a form of agonistic behaviour when the animal feels threatened.

The hyrax does not construct dens, but rather seeks shelter in existing holes of varying size and configuration.
Hyraxes urinate in a designated, communal area. The viscous urine quickly dries and, over generations, accretes to form massive middens. These structures can date back thousands of years. The petrified urine itself is known as hyraceum and serves as a record of the environment, as well as being used medicinally and in perfumes.

Hyraxes inhabit rocky terrain across sub-Saharan Africa and the Middle East. Their feet have rubbery pads with numerous sweat glands, which may help the animal maintain its grip when quickly moving up steep, rocky surfaces. Hyraxes have stumpy toes with hoof-like nails; four toes are on each front foot and three are on each back foot.
They also have efficient kidneys, retaining water so that they can better survive in arid environments.

Female hyraxes give birth to up to four young after a gestation period of seven to eight months, depending on the species. The young are weaned at 1–5 months of age, and reach sexual maturity at 16–17 months.

Hyraxes live in small family groups, with a single male that aggressively defends the territory from rivals. Where living space is abundant, the male may have sole access to multiple groups of females, each with its own range. The remaining males live solitary lives, often on the periphery of areas controlled by larger males, and mate only with younger females.

Hyraxes have highly charged myoglobin, which has been inferred to reflect an aquatic ancestry.

Similarities with Proboscidea and Sirenia

Hyraxes share several unusual characteristics with mammalian orders Proboscidea (elephants and their extinct relatives) and Sirenia (manatees and dugongs), which have resulted in their all being placed in the taxon Paenungulata. Male hyraxes lack a scrotum and their testicles remain tucked up in their abdominal cavity next to the kidneys,
as do those of elephants, manatees, and dugongs.
Female hyraxes have a pair of teats near their armpits (axilla), as well as four teats in their groin (inguinal area); elephants have a pair of teats near their axillae, and dugongs and manatees have a pair of teats, one located close to each of the front flippers.
The tusks of hyraxes develop from the incisor teeth as do the tusks of elephants; most mammalian tusks develop from the canines. Hyraxes, like elephants, have flattened nails on the tips of their digits, rather than the curved, elongated claws usually seen on mammals.

Evolution

All modern hyraxes are members of the family Procaviidae (the only living family within Hyracoidea) and are found only in Africa and the Middle East. In the past, however, hyraxes were more diverse and widespread. At one site in Egypt, the order first appears in the fossil record in the form of '' Dimaitherium'', 37 million years ago, but much older fossils exist elsewhere. For many millions of years, hyraxes, proboscideans, and other afrotherian mammals were the primary terrestrial herbivores in Africa, just as odd-toed ungulates were in North America.

Through the middle to late Eocene, many different species existed. The smallest of these were the size of a mouse but others were much larger than any extant relatives. '' Titanohyrax'' could reach or even as much as over . '' Megalohyrax'' from the upper Eocene-lower Oligocene was as huge as a tapir.
During the Miocene, however, competition from the newly developed bovids, which were very efficient grazers and browsers, displaced the hyraxes into marginal niches. Nevertheless, the order remained widespread and diverse as late as the end of the Pliocene), ultimately giving rise to the elephant family and perhaps also the sirenians. DNA evidence supports this hypothesis, and the small modern hyraxes share numerous features with elephants, such as toenails, excellent hearing, sensitive pads on their feet, small tusks, good memory, higher brain functions compared with other similar mammals, and the shape of some of their bones.

Hyraxes are sometimes described as being the closest living relative of the elephant, although this is disputed. Recent morphological- and molecular-based classifications reveal the sirenians to be the closest living relatives of elephants. While hyraxes are closely related, they form a taxonomic outgroup to the assemblage of elephants, sirenians, and the extinct orders Embrithopoda and Desmostylia.

The extinct meridiungulate family Archaeohyracidae, consisting of seven genera of notoungulate mammals known from the Paleocene through the Oligocene of South America,
is a group unrelated to the true hyraxes.

List of genera

Hyracoidea

* '' Dimaitherium''
* '' Helioseus''?
* '' Microhyrax''
* '' Seggeurius''
* Geniohyidae
** '' Brachyhyrax''
** '' Bunohyrax''
** '' Geniohyus''
** '' Namahyrax''
** '' Pachyhyrax''
* "Saghatheriidae"
** '' Megalohyrax''
** '' Regubahyrax''
** '' Rukwalorax''
** '' Saghatherium''
** '' Selenohyrax''
** '' Thyrohyrax''
* Titanohyracidae
** '' Afrohyrax''
** '' Antilohyrax''
** '' Rupestrohyrax''
** '' Titanohyrax''
* Pliohyracidae
** '' Hengduanshanhyrax''
** '' Kvabebihyrax''
** '' Meroehyrax''
** '' Parapliohyrax''
** '' Pliohyrax''
** '' Postschizotherium''
** '' Prohyrax''
* Procaviidae
** '' Dendrohyrax''
** '' Gigantohyrax''
** '' Heterohyrax''
** '' Procavia''

Extant species

In the 2000s, taxonomists reduced the number of recognized species of hyraxes. In 1995, they recognized 11 species or more. However, as of 2013, only four were recognized, with the others all considered as subspecies of one of the recognized four. Over 50 subspecies and species are described, many of which are considered highly endangered. The most recently identified species is '' Dendrohyrax interfluvialis'', which is a tree hyrax living between the Volta and Niger rivers but makes a unique barking call that is distinct from the shrieking vocalizations of hyraxes inhabiting other regions of the African forest zone.

The following cladogram shows the relationship between the extant genera:

Human interactions

Biblical references

References are made to hyraxes in the Hebrew Bible

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