The southern white rhinoceros or southern square-lipped rhinoceros (Ceratotherium simum simum), is one of the two subspecies of the white rhinoceros. It is the most common and widespread subspecies of rhinoceros. As of late December 2007, the total population was estimated at 17,460 southern white rhino in the wild, making them by far the most abundant subspecies of rhino in the world. South Africa is the stronghold for this subspecies (93.0%), conserving 16,255 individuals in the wild in 2007. However, the current census from Save the Rhino's official website revealed there are 19,682–21,077 southern white rhinoceros since 2015. The southern white rhinoceros is the nominate subspecies, which was given the scientific name Ceratotherium simum simum by the English explorer William John Burchell in the 1810s. Other names were also proposed for the southern subspecies. The subspecies is also known as Burchell's rhinoceros (Ceratotherium simum burchellii) after William John Burchell and Oswell's rhinoceros (Ceratotherium simum oswellii) after William Cotton Oswell respectively. However, they are considered as synonyms to its original scientific name. Ceratotherium simum kiaboaba (or Rhinoceros kiaboaba), also known as straight-horned rhinoceros, was proposed as a different variety found near Lake Ngami and north of the Kalahari desert. However, it was discovered to be an actual southern white rhinoceros. Following the phylogenetic species concept, recent research in 2010 has suggested the southern and northern white rhinoceros may be different species, rather than subspecies of white rhinos, in which case the correct scientific name for the northern subspecies is Ceratotherium cottoni and the southern subspecies should be known as simply Ceratotherium simum. Distinct morphological and genetic differences suggest the two proposed species have been separated for at least a million years. The southern white rhinoceros is one of largest and heaviest land animals in the world. It has an immense body and large head, a short neck and broad chest. Females weigh 1,700 kg (3,750 lb) and males 2,300 kg (5,070 lb). The head-and-body length is 3.4–4 m (11.2–13.1 ft) and a shoulder height of 160–186 cm (5.25–6.10 ft). On its snout it has two horns. The front horn is larger than the other horn and averages 60 cm (24 in) in length and can reach 150 cm (59 in). Females usually have longer but thinner horns than the males which is larger but shorter. The southern white rhinoceros also has a prominent muscular hump that supports its relatively large head. The colour of this animal can range from yellowish brown to slate grey. Most of its body hair is found on the ear fringes and tail bristles, with the rest distributed rather sparsely over the rest of the body. Southern white rhinos have the distinctive flat broad mouth that is used for grazing.