Ceratotherium Simum

The white rhinoceros, also known as the white rhino or square-lipped rhinoceros (''Ceratotherium simum''), is the largest extant species of rhinoceros and the most social of all rhino species, characterized by its wide mouth adapted for grazing. The species includes two subspecies with dramatically different conservation outlooks: the southern white rhinoceros, with an estimated 17,464 individuals in the wild as of the end of 2023, and the northern white rhinoceros. The northern subspecies is critically endangered and on the brink of extinction; its last known male, Sudan, died in March 2018, leaving behind only a very small number of females in captivity. Both subspecies have faced significant threats, primarily from poaching for their horns and habitat loss, which contribute to the species' overall conservation status of Near Threatened.

Naming

One popular, though widely discredited, theory for the origin of the name "white rhinoceros" is a mistranslation of the Dutch word "wijd" (meaning "wide" in English) into English. The term "wide" would have referred to the rhinoceros's broad, square mouth, distinguishing it from the narrow-lipped black rhinoceros. According to this theory, early English-speaking settlers in South Africa misinterpreted "wijd" as "white." Ironically, Dutch and Afrikaans later adopted "white rhino" (e.g., ''witrenoster'' in Afrikaans) as a calque from English, a development suggesting the English term was established before any potential codification of "wijd" by Dutch writers for this species. However, a review of Dutch and Afrikaans literature by Rookmaaker (2003) found no written evidence of "wijd" ever being used to describe the rhinoceros, indicating its use, if any, was likely confined to oral language.

An alternative, more descriptive name for the white rhinoceros is the square-lipped rhinoceros, though it is less commonly used.

The generic name, ''Ceratotherium'', was given by zoologist John Edward Gray in 1868. It derives from the Greek ''keras'' (κέρας), meaning "horn," and ''thērion'' (θηρίον), meaning "beast." The specific epithet, ''simum'', comes from the Greek ''simos'' (σιμός), meaning "flat-nosed," referring to the animal's broad, flat snout.

Taxonomy and evolution

The modern white rhinoceros was initially thought to be descended from ''Ceratotherium praecox'', a species from approximately 7 million years ago with remains found at Langebaanweg near Cape Town. However, a 2005 review of African fossil rhinos by Denis Geraads proposed that while the Langebaanweg species belongs to the genus ''Ceratotherium'', it is not ''C. praecox''. Geraads argued that the type specimen of ''C. praecox'' exhibits closer affinities with the black rhinoceros ('' Diceros bicornis'') and should therefore be classified as '' Diceros praecox''. It had been suggested by Turner (2004) that the modern white rhino's elongated skull—compared to that attributed to ''C. praecox''—evolved to facilitate grazing on shorter grasses as Africa experienced long-term drying conditions. If ''C. praecox'' is indeed ''Diceros praecox'', its shorter skull could instead indicate a browse diet. Further complicating this interpretation, carbon isotope analysis of teeth from fossils assigned to ''Ceratotherium'' at Makapansgat, South Africa, indicated that these animals incorporated over 30% browse into their diet, unlike the exclusively grass-eating modern ''Ceratotherium simum''. Based on these considerations, Geraads (2005) proposed an alternative lineage for the white rhino: '' Ceratotherium neumayri'' → '' Ceratotherium mauritanicum'' → ''C. simum'', with the Langebaanweg rhinos considered an as-yet-unnamed ''Ceratotherium'' species, and black rhinos descending from ''C. neumayri'' via ''Diceros praecox''.

An alternative evolutionary scenario was proposed by Hernesniemi et al. (2011). This model posits ''Ceratotherium efficax'' (now considered synonymous with ''C. mauritanicum'') from the Late Pliocene of Ethiopia and Early Pleistocene of Tanzania as the earliest African ''Ceratotherium''. This species is then proposed to have diversified into '' C. mauritanicum'' in northern Africa, '' C. germanoafricanum'' in East Africa (both now extinct), and the extant ''C. simum''. ''C. germanoafricanum'' is noted as being very similar to ''C. simum'' and has often been regarded as a fossil and ancestral subspecies of the latter. The 2011 study also casts doubt on the Miocene species '' Ceratotherium neumayri'' from southern Europe being ancestral to African species.

It is likely that the common ancestor of both black and white rhinos was a mixed feeder, with the two lineages subsequently specializing in browsing and grazing, respectively. The oldest definitive fossil record of ''Ceratotherium simum'' dates to the mid-Early Pleistocene, around 1.8 million years ago, at Olduvai Gorge in Tanzania.

Southern white rhinoceros

As the end of 2023, an estimated 17,464 southern white rhinos (''Ceratotherium simum simum'') lived in the wild, making them by far the most abundant rhinoceros subspecies globally and outnumbering all other rhino subspecies combined. South Africa is the primary stronghold, home to 12,968 individuals in 2021. Smaller reintroduced populations exist within the subspecies' historical range in Namibia, Botswana, Zimbabwe, Uganda, and Eswatini, with a small population also surviving in Mozambique. Additionally, populations have been introduced outside their former range to Kenya and Zambia.

Northern white rhinoceros

The northern white rhinoceros (''Ceratotherium simum cottoni''), also known as the northern square-lipped rhinoceros, is critically endangered and possibly extinct in the wild. This subspecies, a grazer of grasslands and savanna woodlands, was formerly found in several countries in East and Central Africa south of the Sahara.

The recent population decline has been stark. Initially, six northern white rhinoceros were managed at Dvůr Králové Zoo in the Czech Republic. In 2009, four of these (the only ones capable of reproduction at the time) were transported to Ol Pejeta Conservancy in Kenya, in hopes that a more natural environment would stimulate breeding and save the subspecies. However, the population continued to dwindle: one of the remaining rhinos in the Czech Republic died in May 2011, and the last two bulls capable of natural mating died in 2014 (Suni in Kenya on 18 October, and Angalifu in San Diego on 15 December).Young, Ricky (14 December 2014
Rare white rhino dies at safari park
''U-T San Diego''. Retrieved 25 March 2018. The last remaining male, Sudan, who had been under 24-hour armed guard at Ol Pejeta, was euthanized on 19 March 2018 due to age-related health complications. This left only two females, Najin and Fatu, alive, both residing at Ol Pejeta. With Sudan having been the last male, staff at Ol Pejeta hold hope in using his stored semen, potentially alongside samples from other previously deceased males, for artificial insemination and other assisted reproductive technologies. However, significant challenges persist, including those related to the quality of semen from aged animals like Sudan and the overall complexities of these advanced procedures.

The taxonomic status of the northern white rhinoceros has also been debated. Following the phylogenetic species concept, research by Groves et al. (2010) proposed that it should be considered a distinct species, ''Ceratotherium cottoni'', rather than a subspecies of ''C. simum''. Their analysis suggested that distinct morphological and genetic differences indicate the two lineages may have been separated for at least one million years. However, these findings have not been universally accepted by the scientific community, and the IUCN continued to assess ''C. s. cottoni'' as a subspecies of the white rhinoceros as of 2020.

Description

The white rhinoceros is the largest of the five living rhinoceros species and one of the largest megafauna in existence. Judged by mean body mass, only the three extant species of elephant surpass it. Though the body mass of individual rhinoceros often overlap with that of individual hippopotamuses, with whom it shares a habitat, the white rhinoceros weighs more on average. The white rhino's mass is evident in its large, barrel-shaped body and its immense head, which are connected by a short, powerful neck.

Males (bulls) typically have a head-and-body length of and a shoulder height of , while females (cows) measure in head-and-body length and at the shoulder. The tail adds approximately to the total length. Bulls are heavier, averaging , compared to cows, which average about . While specimens up to are considered reliably recorded, claims of individuals reaching up to remain unverified, making the species' maximum attainable size not definitively known.

The white rhinoceros's most noticeable features are perhaps the two formidable, horn-like structures on its snout, one behind the other. These are not true horns in the bovid sense (which encase a bony core), nor are they antlers of bone like those of deer. Instead, they are solid masses of densely compacted keratin fibers, the same protein that forms human hair and fingernails. The anterior (front) horn is typically the larger and more prominent, averaging in length, though in some individuals, particularly cows, it can attain lengths of up to . A single horn can weigh around , a testament to its dense and substantial structure.

A prominent muscular hump is situated on the back of its neck, crucial for supporting the weight of its massive head during long periods of grazing. Due to its habit of wallowing in mud, the rhino's thick, armor-like skin, typically grey, often takes on the color of the local soil—from yellowish-brown to darker slate. This behavior provides vital protection from the harsh African sun and relief from biting insects. Its only discernible hair is sparse, mostly found as delicate fringes on the ears and short bristles on the tail. Its sturdy, pillar-like legs terminate in broad, stumpy feet, each bearing three large toes that splay slightly to effectively distribute its weight across varied terrain.

The white rhinoceros's most distinctive feeding adaptation is its broad, straight, square-lipped mouth, a feature that allows it to graze efficiently, cropping wide swaths of grass with each pass. It relies less on its sight, which is relatively poor, and more on its other highly developed senses. Its large, tubular ears are capable of swiveling independently in a wide arc, allowing the rhino to accurately discern the direction of even subtle sounds and perceive potential threats, especially in dense vegetation. White rhinoceros also have a highly developed sense of smell; its olfactory passages are actually larger than its brain, and its muzzle houses the widest set of nostrils of any land-based animal.

Genome

Understanding the genetic makeup of the white rhinoceros is increasingly important for informing conservation strategies, particularly for the critically endangered northern subspecies, and for deeper insights into its evolutionary biology. Key genomic characteristics include:

The genome size of the southern white rhinoceros (''Ceratotherium simum simum''), based on sequencing efforts, is approximately 2.58 Gbp (gigabase pairs), which is equivalent to 2581.22 Mb (megabases). Genetically, white rhinoceros diploid cells possess a total of 82 chromosomes. This complement comprises 40 pairs of autosomes (non-sex chromosomes) and one pair of sex chromosomes (typically XX in females and XY in males).

Behavior and ecology

White rhinos are specialized grazing herbivores, primarily inhabiting grassland and savanna ecosystems. They show a preference for the shortest grass grains and are recognized as one of the largest dedicated grazers. Their daily routine involves considerable time spent feeding—often around half the day—with about a third dedicated to resting, and the remainder to other activities. If water is readily available, they typically drink twice a day, but in arid conditions, they demonstrate remarkable resilience, capable of surviving four or five days without water. Like all rhinoceros species, white rhinos frequently indulge in mud wallows, coating their skin to assist in thermoregulation, protect against sunburn, and deter biting insects. As megaherbivores, white rhinos are considered significant ecological engineers; their grazing patterns are thought to shape grassland structure and savanna ecology. Similar to the impact of African elephants, they are believed to be a driving factor in their ecosystems, and the loss of such large herbivores can trigger serious cascading negative effects, potentially harming numerous other species.

White rhinos employ a range of vocalizations for communication. These include a panting contact call, grunts and snorts during courtship rituals, squeals of distress when alarmed, and deep bellows or growls when threatened. Threat displays, particularly by bulls, involve visually intimidating behaviors such as wiping their horns on the ground and adopting a head-low posture with ears flattened back, often accompanied by aggressive snarls and shrieks if an attack is imminent. Vocalizations can differ significantly between the northern and southern white rhinoceros, and even panting contact calls can vary between individuals within each subspecies, aiding in individual recognition and long-distance communication. Despite their bulk, white rhinos are surprisingly quick and agile, capable of running at speeds up to .

Socially, white rhinos often form groups called 'crashes' or herds, typically comprising up to 14 individuals, mostly females and their calves. Sub-adult bulls may also congregate, sometimes associating with an adult cow. However, most adult bulls lead a solitary existence. Dominant bulls are highly territorial and invest significant effort in marking their domain. This involves creating well-defined dung piles, known as middens; a bull might maintain 20 to 30 such piles to signal his presence to other rhinos. Other marking behaviors include rubbing their horns on bushes or the ground and scuffing the earth with their feet before urine spraying. These patrols and marking activities can occur frequently, sometimes up to ten times an hour within a bull's territory. A similar scrape-marking ritual, but without urine spraying, is also a common territorial display. Subordinate bulls, in contrast, do not establish or mark territories. The most intense conflicts between bulls typically erupt over mating rights with receptive females. Cows, for their part, have territories that overlap extensively, and they do not engage in territorial defense.

Reproduction

Females (cows) typically reach sexual maturity between 6 and 7 years of age, whereas males (bulls) mature later, usually between 10 and 12 years. Courtship among white rhinos is often a prolonged and sometimes arduous affair. A persistent bull will often stay near a cow even when she acts aggressively, emitting calls as he approaches. He may chase or block the cow's path, vocalizing with loud squeals or wails if she attempts to leave his territory. When a cow is ready to mate, she signals her receptiveness by curling her tail and adopting a rigid stance during the copulation, which lasts about half an hour. Breeding pairs may remain together for 5 to 20 days before separating.

The gestation period for a white rhino is approximately 16 months, after which a single calf is born, usually weighing between . Newborn calves are unsteady on their feet for the first two to three days of life. When feeling threatened, a young calf will instinctively run in front of its mother, who is fiercely protective and will vigorously defend her offspring. Weaning typically begins when the calf is around two months old, but it may continue to suckle for more than a year. The birth interval for white rhinos generally ranges from two to three years. Before giving birth to a new calf, a mother will usually chase off her current, older calf. The typical lifespan of a white rhinoceros is estimated to be 40–50 years, though comprehensive longevity studies with robust contemporary sourcing are still needed to refine this figure.

Owing to their immense size and formidable presence, adult white rhinos are largely invulnerable to natural predators, with humans being their only significant and consistent threat. Calves are also well-protected by their mothers' vigilance and their own developing tough hides. Attacks are exceedingly rare, though isolated incidents, such as a documented successful predation by a lion pride on an ailing adult bull weighing in Mala Mala Game Reserve, South Africa, have occurred.

Distribution

The southern white rhinoceros (''Ceratotherium simum simum'') is predominantly found in Southern Africa and represents a significant conservation achievement. After facing near extinction in the early 20th century, the subspecies made a remarkable recovery. As the end of 2023, the wild population was estimated at 17,464 individuals, solidifying its status as the most numerous rhinoceros subspecies. The overwhelming majority of these animals reside in South Africa (approximately 12,968 in 2021), with other key populations located in Namibia, Botswana, Zimbabwe, and Kenya. Smaller populations, many resulting from reintroduction efforts, also exist in Eswatini, Uganda, and Zambia, while a few persist in Mozambique.

In stark contrast, the northern white rhinoceros (''Ceratotherium simum cottoni'') is critically endangered and teeters on the brink of extinction. Historically, its range extended across several countries in East and Central Africa, including northwestern Uganda, southern Chad, southwestern Sudan, the eastern Central African Republic, and northeastern Democratic Republic of the Congo (DRC). The subspecies' last known wild stronghold was Garamba National Park in the DRC. However, relentless poaching led to a catastrophic decline; surveys in August 2005 found only four individuals remaining in Garamba,International Rhino Foundation. 2002
Rhino Information – Northern White Rhino
Archived 23 October 2007. Retrieved 19 September 2006. and by June 2008, it was widely reported that the northern white rhino might be extinct in the wild. Currently, the subspecies is considered possibly extinct in the wild, with only two females surviving under managed care in Kenya (as detailed in the 'Northern white rhinoceros' section under Taxonomy and evolution).

Both white rhinoceros subspecies have endured severe threats from habitat loss and, most devastatingly, from persistent poaching. Organized poaching syndicates, which have historically included groups like the Janjaweed in specific regions, have been responsible for dramatically reducing rhino numbers. The primary driver for this illicit trade is the high value placed on rhino horn in some traditional Asian medicines—despite a complete lack of scientific evidence supporting any medicinal benefits—and, increasingly, for its use in ornamental carvings or as a status symbol.

Poaching

Historically, uncontrolled hunting during the colonial era significantly reduced white rhino populations. Today, however, the most urgent and persistent threat is poaching, driven by the high value of rhino horns on the illegal market. The white rhino's large size, relatively placid nature, poor eyesight, and tendency to live in herds can make it particularly vulnerable to poachers.

The demand for rhino horn is primarily fueled by its use in some traditional Asian medicines, where it is ground into powder or processed into tablets for a variety of unproven remedies for ailments ranging from fevers to cancer. This demand persists despite a complete lack of scientific evidence for any medicinal properties; rhino horn is composed of keratin, the same protein found in human fingernails and hair. The lucrative nature of this illicit trade has led to the rise of highly organized, transnational criminal syndicates that equip poaching teams with advanced technology, including night vision equipment, silenced weapons, veterinary tranquilizers, and occasionally helicopters. For the northern white rhinoceros, ongoing conflicts in regions like the Democratic Republic of Congo and incursions by heavily armed poachers, sometimes from neighboring countries like Sudan, critically undermined efforts to protect the last wild populations.

Poaching levels surged dramatically in the early 21st century. For instance, in South Africa, the country with the largest rhino population, poaching incidents escalated sharply; official statistics showed that rates nearly doubled in 2013 compared to the previous year. This intense pressure contributes to the white rhinoceros's overall IUCN status as Near Threatened. Mozambique has been identified as a significant transit route for rhino horn smuggled out of South Africa; as of 2014, its domestic laws reportedly treated rhino poaching as a misdemeanor, although international pressure has since encouraged legislative reforms. The impact is starkly illustrated in key rhino strongholds: the white rhino population in South Africa's renowned Kruger National Park, for example, declined by approximately 60% between 2013 and 2021, to an estimated 3,529 individuals, largely due to poaching.

The global reach of this criminal enterprise was highlighted in March 2017, when poachers infiltrated the Thoiry Zoo in France and killed Vince, a southern white rhinoceros, removing his horn. This brazen attack is believed to be the first such fatal poaching incident at a European zoo.

Despite significant anti-poaching efforts across many African nations, the immense profits associated with rhino horn continue to incentivize poachers, who often risk severe penalties. On the black market, particularly in parts of Asia, rhino horn can command prices equivalent to tens of thousands of US dollars per kilogram, sometimes exceeding the value of gold by weight. Poaching operations have also adapted to modern technology, reportedly using social media to gather intelligence on rhino locations by searching for geotagged images posted by unsuspecting tourists at wildlife attractions like Kruger National Park.

Modern conservation tactics

With the northern white rhinoceros (NWR) being critically endangered and reduced to only two known individuals globally (females Najin and Fatu, both in captivity), conservation efforts have predominantly focused on intensive management and pioneering assisted reproductive technologies (ART) to prevent the subspecies' complete extinction. A pivotal early strategy was the translocation on December 20, 2009, of four NWRs—including Najin and Fatu, who were among the few reproductively viable individuals—from Dvůr Králové Zoo in the Czech Republic to the Ol Pejeta Conservancy in Kenya. The primary hope was that a more naturalistic environment, combined with enhanced security and a carefully managed diet, might stimulate natural breeding.

When natural breeding attempts proved unsuccessful, Ol Pejeta Conservancy explored other avenues. In February 2014, a fertile southern white rhinoceros bull from the Lewa Wildlife Conservancy was introduced into an enclosure with the NWR females. This initiative aimed to assess the potential for cross-breeding as a means to preserve some NWR genetic legacy and to possibly stimulate the females' reproductive cycles. However, this effort did not lead to any reported pregnancies or successful inter-subspecies matings.

More recent conservation efforts have centered on advanced ART. A significant breakthrough was announced on August 22, 2019, when scientists successfully fertilized NWR eggs (oocytes harvested from Najin and Fatu) using (ICSI) with cryopreserved semen from deceased NWR bulls, namely Saut and Suni. (Semen from Sudan, the last NWR male who died in 2018, had also been collected and cryopreserved for such efforts). These procedures resulted in the creation of viable NWR embryos: two were announced on September 11, 2019, followed by a third (all reportedly from Fatu's eggs) on January 15, 2020. These precious embryos are currently stored in a frozen state, with plans for their eventual transfer into surrogate southern white rhinoceros females in hopes of producing NWR calves.

In captivity

The vast majority of white rhinos in zoos and wildlife parks globally are southern white rhinos (''Ceratotherium simum simum''). In 2021, their worldwide captive population was estimated to be over 1,000 individuals.
Wild-caught southern white rhinos have demonstrated a good capacity to breed in captivity, provided they are given adequate space, appropriate nutrition, and the presence of other breeding-age females. However, a persistent challenge in captive management is the notably low rate of reproduction among captive-born southern white females, a phenomenon for which the underlying reasons are still not fully understood and are subject to ongoing research.

Regarding the northern white rhinoceros (''Ceratotherium simum cottoni''), the San Diego Zoo Safari Park in California, United States, played a significant role in attempting to conserve the subspecies. The park housed two NWRs on loan from the Dvůr Králové Zoo: Angalifu, a wild-caught male who died of old age on December 14, 2014, and Nola, a female born in 1974, who was euthanized on November 22, 2015, due to declining health. These deaths, along with the death of Suni (one of the males translocated to Kenya) in 2014, and later Sudan in 2018, left Najin and Fatu as the sole survivors. These two females reside at the Ol Pejeta Conservancy in Kenya, where they were transferred in 2009 from Dvůr Králové Zoo as part of the critical effort to conserve the subspecies in its natural habitat range. They remain under constant 24-hour armed guard to protect them from poaching threats.

References

Notes

External links

White Rhino Information
from the Rhino Resource Center.

White Rhino Pictures
from the Rhino Resource Center.

White Rhino entry
on the International Rhino Foundation website (archived 10 December 2008).

White Rhino entry
on the World Wide Fund for Nature website (archived 5 July 2008).

White Rhinoceros page
at the Honolulu Zoo (archived 2 April 2012).


from the San Diego Zoo (archived 30 January 2009).

White Rhinoceros page
at the Philadelphia Zoo (archived 3 March 2006).

Narrated video about the White Rhinoceros
from Biocrawler.com (archived 6 February 2008).


from WildlifeAfrica.co.za.


.

Poachers kill one of last two white rhinos in Zambia
(AFP news, archived 18 June 2007).

Rhino Webcam at Zoo Budapest
(archived 16 March 2013).


.
*
* at the UCSC Genome Browser.

People Not Poaching
The Communities and IWT Learning Platform.

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Dicerotini
Mammals of the Central African Republic
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