Hyraxes, also known as dassies or rock rabbits, are small, furry mammals belonging to the order Hyracoidea. They are rodent-like in appearance and are often mistaken for marmots and capybaras. However, hyraxes are phylogenetically most closely related to elephants and sirenians and, together with them, constitute the grandorder Paenungulata.
They are characterized by short tails and flattened hoof-like nails on their toes. Another distinguishing feature of this group is the presence of rubbery pads and sweat glands on their feet, which help improve their grip on hard surfaces.
There are 6 extant species of hyraxes across 3 genera: Heterohyrax, Procavia, and Dendrohyrax. The genus Dendrohyrax comprises four species: the Southern, Eastern, Western, and Benin tree hyraxes. In contrast, both Procavia and Heterohyrax are monotypic, with Procavia represented solely by the rocky hyrax and Heterohyrax by the yellow-spotted rock hyrax (bush hyrax).
Although once widespread, these mammals are currently restricted to sub-Saharan Africa, with only one species, the rock hyrax, found in the Middle East.
Most hyraxes measure between 12 and 28 in (30 and 70 cm) in length and weigh around 4 to 11 lb (2 to 5 kg). However, some older forms, like Titanohyrax ultimus (the largest known extinct hyrax), were as large as rhinoceroses, weighing around 1,300 to 2,900 lb (600 to 1,300 kg).
Male and female hyraxes are approximately the same size.
These animals have stocky, densely furred bodies, with tails and necks notably short in proportion to their overall length. All hyraxes have four stumpy toes on each front foot, but, on the hindfoot, most species have three toes. Only the tree hyraxes possess four toes on each hind foot.
All the front toes have flattened, hoof-like nails, which help these animals grip rough surfaces, like rocks and tree trunks. The first and third toes of the hind foot also bear these nails, but the second toe is modified to form a long, curved claw, which helps in grooming the fur.
Their body color varies from gray to brown, depending on the species. While many species, like the rock hyrax, have lighter, creamy undersides, others, like the bush hyrax, sometimes have yellow spots, particularly on their back.
Compared to those of similarly sized mammals, hyrax skulls are characterized by a short rostrum, small auditory bullae, and a relatively large jugal bone. A series of postorbital processes form a prominent postorbital bar, a trait rare among small mammals.
Hyraxes have two enlarged, tusk-like upper incisors that grow continuously throughout their lives, much like those of elephants. The lower incisors are deeply grooved and comb-like in appearance.
The cheek teeth are separated from the incisors by a wide gap called the diastema. The molars have multiple lophs or ridges, an adaptation to the fibre-rich herbivorous diet of hyraxes. While rock hyraxes have hypsodont dentition with high crowns and relatively short roots, tree and bush hyraxes have brachydont dentition with short crowns and relatively long roots.
These animals derive their name, hyrax, from the Greek word hurax, which translates to a ‘shrewmouse’. This etymology stems from the similarities hyraxes share with rodents in terms of their body shape and size. However, they are phylogenetically related to the orders Proboscidea (elephants) and Sirenia (sirenians)[1]. Together, these three groups constitute the grandorder Paenungulata. This relation is based on some similarities that these animals share.
In 1995, scientists recognized 11 species of hyraxes, but currently, there are 6 species (under 3 genera). The most recently identified species, the Benin tree hyrax, Dendrohyrax interfluvialis, is found in the region between the Volta and Niger rivers and is distinguished by its unique barking call.
Hyraxes are believed to have evolved along with elephants and sirenians from their common afrotherian ancestors. While one lineage gave rise to small terrestrial hyraxes, others evolved into large-bodied terrestrial elephants and fully aquatic sirenians.
They had reached the peak of their diversity between the Middle and Late Eocene Epoch. Of all species that existed during that time, the smallest were no more than the size of a mouse. The larger species, like those in the genera Titanohyrax and Megalohyrax, weighed over 2,900 lb (1,300 kg)[2].
During the Miocene Epoch, hyraxes faced increasing competition from bovids, which were highly efficient grazers and browsers, gradually encroaching on their ecological niches. By the Pliocene Epoch, around two million years ago, hyraxes were widespread across Europe, Asia, and Africa. However, with time, these animals became restricted to the African subcontinent and were wiped out of their former ranges.
The rock and bush hyraxes are found in the rocky terrains of sub-Saharan Africa. The rock hyrax is the only hyrax species that is found in the adjacent parts of the Middle East. In East Africa, this species is found at sea level as well as at altitudes of up to 14,000 ft (4,000 m)[3].
The four species of tree hyraxes are primarily arboreal, taking shelter in tree hollows and dense vegetation. The rock and bush hyraxes inhabit rock outcrops and cliffs across much of their range, including Ethiopia. These two species also occupy isolated granite outcrops (koppies) in the southern parts of Africa.
They are primarily herbivorous, feeding on grasses, herbs, fruits, and tree bark. However, the rock hyrax occasionally supplements its diet with insects, lizards, and bird eggs[4].
While rock and bush hyraxes are active during the day (diurnal), spending most of their time sunbathing, tree hyraxes are nocturnal and forage at night.
Since they do not efficiently regulate their internal body temperature, rock and bush hyraxes often huddle together to keep themselves warm (behavioral thermoregulation).
Rock hyraxes live in groups of 10 to 80 individuals, depending primarily on habitat quality and predation pressure[5]. These groups are led by a single male who owns a territory and actively defends it from rivals. This male often has exclusive access to a core group of females within his range, while the subordinate males, living in the periphery of the areas controlled by the superior male, mate occasionally, usually with younger females.
Bush hyraxes are social, too, but they typically form much smaller groups, comprising 5 to 30 individuals.
Tree hyraxes are particularly less social and prefer living in pairs rather than large groups.
These animals, especially rock hyraxes, set out on short-feeding excursions when needed. They are extremely cautious eaters and quickly bite off a mouthful of grass or leaves while watching out for predators lurking nearby. Unlike most grazing or browsing mammals, hyraxes use their molars to tear plant parts instead of their incisors.
When rock and bush hyraxes are threatened during feeding, the territorial male signals the group with an alarm call, and all individuals scurry to safer areas, where they remain motionless till the threat subsides.
They can survive without drinking water for prolonged periods, relying solely on the moisture obtained from food.
Although not ruminants, they have a multi-chambered stomach that allows symbiotic bacteria to break down plant matter. However, their ability to digest fibers is less than that of the ungulates.
Their lifespan typically ranges between 9 to 14 years.
Female hyraxes undergo an extraordinarily long gestation period of about 7 to 8 months (for an animal of this size), after which they give birth to young. While bush and tree hyraxes have 1 to 3 offspring, rock hyraxes may sometimes have up to 4 young. These young are considerably well-developed (precocial), running and hopping within an hour after birth.
The offspring begin to consume vegetation in a couple of days, but continue to suckle till 3 months. They are weaned at 1 to 5 months of age and become sexually mature in 16 to 17 months. After attaining sexual maturity, females typically join the adult female group while males disperse.
Hyraxes are attacked by large mammals, such as lions, leopards, hyenas, jackals, and servals. They are also preyed upon by pythons and large birds, like Verreaux’s eagle (Aquila verreauxii).
These animals are also parasitized by several ectoparasites, like ticks, lice, mites, and fleas, as well as endoparasites, such as nematodes and cestodes.
Of all hyrax species evaluated for the IUCN Red List of Threatened Species, the Eastern tree hyrax has been categorized as Near Threatened (NT). Besides habitat loss due to deforestation, this species is hunted for its fur in the forest belt around Mt. Kilimanjaro, thereby causing a rapid decline in its numbers.
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