| Black rhinoceros|
|Population||Less than 28,000|
|Conservation status||Vulnerable to critically endangered|
Rhinoceros (Greek: ῥῑνόκερως; rhinos and κέρας keras; "nose-horn") refers to several large pachydermatous herbivorous land mammals of Africa and Asia, which bear one or two nasal horns. Rhinoceros have poor vision but a good sense of smell, and despite their size - which is exceeded only by elephants - they can quickly face danger and charge at speeds up to 35 mph.
Rhinos are heavy-bodied animals, bearing a barrel-shaped body on stout, pillar-like legs with three-toed hooves. The skin is thick, grey-colored, and except for the Sumatran rhino (which has a thin coat of extensive body hair) nearly hairless; the Indian and Javan rhinos have a folded skin pattern which gives the animals an appearance of bearing armor plate. Rhinos have low vision, but this disadvantage is offset by a pronounced sense of smell and very good hearing.
Depending on the species, rhinos are 8.2 to 12.4 feet in body length, excluding the tail, and weigh between 2,000 and 5,000 pounds, with several individuals of the white rhinoceros recorded to weigh over 7,000 pounds. The head is large, elongated, and bears the horns for which it is named. The genera Rhinoceros have a single, large horn; the remaining species have two, of which the front horn is longer. Lacking a bony core, these horns are made entirely of keratin - the same material found in hair and fingernails - which continue to grow throughout life. The nasal bone supporting the horns is often massive and clearly arched forward and protrudes over the intermediate jawbone. On the nasal bone there are distinct, "cauliflower" roughened structures on the bone surfaces where the horns begin. The brain case is relatively small for the size of the animal.
Asian rhinoceros have a front dentition with one or two pairs of incisors in the lower and upper jaw; the African species are missing these. The molars have two enamel transverse strips on the occlusal surface (bilophodont). As a general characteristic the enamel on the occlusal surfaces of the anterior two maxillary molars is characteristically "n"-shaped, while on the mandibular molars it is "L"-shaped. The premolars differ only slightly from the molars, and depending on the diet, the molars may be low-crowned or high-crowned (brachyodont or hypsodont).
Five species are in existence today, but severely-reduced in numbers; four species currently are near the brink of extinction as a result of the illegal trade in rhino horns:
- White or square-lipped rhinoceros, Ceratotherium simum
- Black, or hook-lipped rhinoceros, Diceros bicornis
- Greater Indian rhinoceros, Rhinoceros unicornis
- Javan rhinoceros, Rhinoceros sondaicus
- Sumatran rhinoceros, Dicerorhinus sumatrensis
Rhinos today live in sub-Saharan Africa and in South and Southeast Asia both in savannah landscapes and in highland and lowland tropical rainforests. Fossil evidence indicates many species lived in northern Eurasia and North America, with the extinct woolly rhinoceros (Coelodonta antiquitatis) living in subarctic tundra.
Social behavior and reproduction
Rhinos are generally solitary, but can occur in small, matriarchal-organized herds. Bulls are mostly loners and live territorial. The individual animals live in tightly defined areas that are marked with urine and feces. Rhinos are more active during dusk and at night then they are during the daytime. They are shy animals that avoid human contact, so reports of rhino aggressiveness are usually greatly exaggerated. The Asian rhino species, which all have a front dentition, use their horns rarely in battle except with other rhinos; their real weapons are the dagger-like incisors of the lower jaw, with which they tear dangerous and deep wounds. The African rhino species will use their horns as a primary weapon for defense or themselves or territory against other animal species.
After a gestation period of 15 to 18 months, a calf is born, and stays with the mother for two and a half to three years. If a second calf is born during this time the older one is chased away by the mother. The life expectancy is between 30 and a maximum of 50 years. Age determination of fossil species has been made by a comparison to the white rhinoceros and is based on anatomical features such as tooth eruption, degree of use of individual teeth or adhesion stages of certain bone sutures. In general, mammalian life expectancy is closely related to adult body weight and extinct rhinos, which are similar in size to those of today, are likely to be in an equivalent range.
All rhinos feed exclusively on vegetable diet and are adapted to this diet with wide molar teeth. However, the species have specialized in different plant foods, with four of the five rhino species living today subsisting on soft plant foods such as leaves, branches, twigs, buds and fruits via browsing. The molars of these species usually have low dental crowns and less dental cement. In addition, these rhino species have a rather short, rectangular occipital bone due to the high head posture. The white rhinoceros is the only extant species completely adapted to grazing. Since grasses contain silica, which is very hard, it has teeth with high tooth crowns and a high proportion of cementum formed due to the high abrasion during chewing.
The single greatest threat to all species of rhinos is poaching by man, specifically a systematic killing of the animals for their horns, which are used in Chinese folk medicine in addition for use in ceremonial daggers in many Arab cultures. Numbering well over 200,000 head in 1970, the population of these animals is now the following:
- White rhinoceros: 20,170 at end of 2010. Subspecies C. s. cottoni listed as critically endangered, with two females only examples left alive; sole remaining male died on March 20, 2018.
- Black rhinoceros: 4,880 at end of 2010. Critically endangered.
- Indian rhinoceros: 2,575, May, 2007. Vulnerable.
- Javan rhinoceros: 60 animals, estimated in 2008. Critically endangered.
- Sumatran rhinoceros: less than 250, estimated in 2008. Critically endangered
- Evolution of the rhinoceros? Preposterous!. Creation Ministries International. Retrieved on April 30, 2018.