Interactions between individuals usually are avoided, but the square-lipped rhino lives in groups of up to 10 animals. Most rhinoceroses are solitary inhabitants of open grassland, savanna, scrub forest or marsh, but the Sumatran rhino is now found only in deep forest. The feet of the modern species have three short toes, tipped with broad, blunt nails. They are nearly or completely hairless, except for the tail tip and ear fringes, but some fossil species were covered with dense fur. All rhinos are gray or brown in colour, including the white or square-lipped (Ceratotherium simum), which tends to be paler than the others. Rhinoceroses are noted for their thick skin, which forms platelike folds, especially at the shoulders and thighs. Adults of larger species weigh three to five tons. Modern rhinoceroses are large animals, ranging from 2.5 metres (8 feet) long and 1.5 m high at the shoulder, in the Sumatran rhinoceros (Didermocerus or Dicerorhinus, sumatrensis), to about 4.3 m long and 2 m high in the great Indian rhinoceros (R. Modern rhinoceroses are characterized by the possession of one (in the two species of the genus Rhinoceros) or two (in the other three genera) horns on the upper surface of the snout, composed not of true horn but of keratin, a fibrous protein found in hair. The term rhinoceros is sometimes also applied to other, extinct members of the family Rhinocerotidae, a diverse group that includes several dozen fossil genera in addition to the recent ones. plural Rhinoceroses, Rhinoceros or Rhinoceri, any of five species of ponderous, hoofed mammals, family Rhinocerotidae (order Perissodactyla), found in eastern and southern Africa and in tropical Asia.