Hyrax

 

Hyraxes Temporal range: Eocene-Recent, 55.8–0 Ma PreЄ Є O S D C P T J K Pg N
Yellow-spotted hyrax (Heterohyrax brucei)
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Synapsida
Class:	Mammalia
clade:	Atlantogenata
Superorder:	Afrotheria
clade:	Paenungulata
Order:	Hyracoidea Huxley, 1869
Families
†Pliohyracidae Procaviidae

A hyrax (from Greek ὕραξ "shrewmouse") is any species of fairly small, thickset, herbivorous mammals in the order Hyracoidea. The rock hyrax Procavia capensis, the yellow-spotted rock hyrax Heterohyrax brucei, the western tree hyrax Dendrohyrax dorsalis, and the southern tree hyrax, Dendrohyrax arboreus live in Africa and the Middle East.

Hyraxes are well-furred, rotund creatures with short tails. Most measure between 30 and 70 cm long and weigh between 2 and 5 kg.

Characteristics

Tree hyrax in the Serengeti, Tanzania

Hyraxes retain a number of early mammalian characteristics; in particular, they have poorly developed internal temperature regulation (which they deal with by huddling together for warmth, and by basking in the sun like reptiles). Unlike other browsing and grazing animals, they do not use the incisors at the front of the jaw for slicing off leaves and grass, but use the molar teeth at the side of the jaw, instead. The incisors are nonetheless large, and grow continuously through life, in a manner similar to those of rodents. There is a small diastema between the incisors and the cheek teeth. The dental formula for hyraxes is $Upper: 1.0.4.3, lower: 2.0.4.3$.

A hyrax showing the characteristic chewing/grunting behaviour

Although not ruminants, hyraxes have complex, multichambered stomachs that allow symbiotic bacteria to break down tough plant materials, and their overall ability to digest fibre is similar to that of the ungulates. Their mandibular motions (see video) have often been described as chewing cud, although there is no evidence this behaviour is associated with the regurgitation of stomach contents for the extraction of nutrients from coarse, low-grade leaves and grasses, as in the even-toed ungulates and some of the macropods. This behaviour is apparently referred to in a passage in the Bible (Leviticus 11:5) which describes hyraxes as chewing the cud. Some authors believe these chewing motions are a form of antagonistic behavior, when the animal feels threatened, rather than being related to ingestion or mastication.

Hyraxes inhabit rocky terrain across sub-Saharan Africa and the Middle East. Their feet have rubbery pads with numerous sweat glands, which help the animal maintain its grip when moving fast up steep, rocky surfaces. They also have efficient kidneys, retaining water so they can survive in arid environments.

Female hyraxes give birth to up to four young after a gestation period of between seven and eight months, depending on the species. The young are weaned at one to five months of age, and reach sexual maturity at 16 to 17 months. Male hyraxes lack a scrotum, and their testicles remain tucked up in their abdominal cavity next to the kidneys, much like elephants, manatees, and dugongs. Female hyraxes have a pair of teats near their shoulders, as well as four teats in their groin.

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

Historical accounts

Hyrax on Mount Kenya

The words "rabbit", "hare", or "coney" appear as terms for the hyrax in some English translations of the Bible. Early English translators had no knowledge of the hyrax (Hebrew שָּׁפָן shaphan), and therefore no name for them. There are references to hyraxes in the Old Testament, particularly in Leviticus 11, where they are described as lacking a split hoof and therefore being not kosher. It also claims that the hyrax chews its cud. However, this claim is due to the habit of the hyrax chewing without having ingested anything, resembling the chewing of cud. Some of the modern translations refer to them as rock badgers. Shaphan was also the name of a scribe of King Josiah.

Phoenician sailors visiting the coast of Spain circa 1100s BCE, mistaking the European rabbit for the rock hyrax Procavia capensis from their native homeland, gave it the name i-shepan-ham. A theory exists that an adaptation and/or corruption of this name, used by the Romans, became Hispania, leading to English Spain and Spanish España, although this theory is somewhat controversial.

Evolution

All modern hyraxes are members of the family Procaviidae (the only living family within the Hyracoidea) and are found only in Africa and the Middle East. In the past, however, hyraxes were more diverse, and widespread. The order first appears in the fossil record at a site in the Middle East in the form of Dimaitherium, 37 million years ago. For many millions of years, hyraxes were the primary terrestrial herbivore in Africa, just as odd-toed ungulates were in the Americas. Through the middle to late Eocene, there were many different species, the largest of them about the weight of a small horse, the smallest the size of a mouse. During the Miocene, however, competition from the newly developed bovids—very efficient grazers and browsers—pushed the hyraxes out of the prime territory and into marginal niches. Nevertheless, the order remained widespread, diverse and successful as late as the end of the Pliocene (about two million years ago) with representatives throughout most of Africa, Europe and Asia.

The descendants of the giant hyracoids evolved in different ways. Some became smaller, and gave rise to the modern hyrax family. Others appear to have taken to the water (perhaps like the modern capybara), and ultimately gave rise to the elephant family, and perhaps also the sirenians (dugongs and manatees). 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, high brain functions compared to other similar mammals, and the shape of some of their bones.

Hyraxes are sometimes described as being the closest living relative to the elephant. Although relatively closely related, not all scientists support the proposal that hyraxes are the "closest" living relative of the elephant. Recent morphological and molecular-based classifications reveal the sirenians to be the closest living relatives of elephants, while hyraxes are closely related, but form an outgroup to the assemblage of elephants, sirenians, and extinct orders such as Embrithopoda and Desmostylia.

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

List of extinct species

• Pliohyracidae
  • Geniohyinae
    • Seggeurius
    • Geniohyus
  • Saghatheriinae
    • Microhyrax
    • Meroehyrax
    • Selenohyrax
    • Bunohyrax
    • Pachyhyrax
    • Megalohyrax
    • Saghatherium
    • Thyrohyrax
  • Titanohyracinae
    • Antilohyrax
    • Titanohyrax
  • Pliohyracinae
    • Sogdohyrax
    • Kvabebihyrax
    • Prohyrax
    • Parapliohyrax
    • Pliohyrax
    • Postschizotherium
• Procaviidae
  • Procaviinae
    • Gigantohyrax
    • Procavia (Cape Hyrax)
      • Procavia antigua
      • Procavia transvaalensis

Living species

Scientists have recently reduced the number of distinct species of hyrax recognized. As recently as 1995, there were eleven or more recognized species; only four are recognized today. The remaining species are regarded as subspecies of the remaining four. There are over 50 recognized subspecies and species, many of which are considered highly endangered.

• ORDER HYRACOIDEA
  • Family Procaviidae
    • Genus Dendrohyrax
      • Southern Tree Hyrax, Dendrohyrax arboreus
      • Western Tree Hyrax, Dendrohyrax dorsalis
    • Genus Heterohyrax
      • Yellow-spotted Rock Hyrax, Heterohyrax brucei
    • Genus Procavia
      • Rock Hyrax, Procavia capensis