Perissodactyla

Perissodactyla is an order of mammals known as odd-toed ungulates. Its extant members are divided into three families: Equidae (horses, donkeys, zebras), Rhinocerotidae (rhinoceroses), and Tapiridae (tapirs). A defining feature is a mesaxonic limb structure, with the axis running through the third toe, which is typically the dominant weight-bearing digit. The number of toes varies by family: equids have a single functional toe per foot, rhinos have three, and tapirs have four on the front feet and three on the hind feet.

Anatomy and diet: Perissodactyls are hindgut fermenters with a relatively simple stomach and a large caecum, enabling digestion of fibrous vegetation. Their cheek teeth are high-crowned and shaped for grazing or browsing, reflecting a herbivorous diet. Limbs are adapted for varied locomotion, from fast running in horses to more ponderous movement in rhinos and tapirs.

Distribution and ecology: Today, rhinos occur in Africa and parts of Asia; tapirs are found in tropical Central and South America and Southeast Asia; equids have held a wide native range in parts of Africa, Asia, and Europe, with many species now domesticated. They inhabit a range of habitats, including grasslands, forests, and tropical environments. Reproduction involves relatively long gestation periods, with usually a single offspring per birth.

Evolution and conservation: Perissodactyls originated in the early Paleogene, reaching peak diversity in the Eocene before declining due to climate change and competition with artiodactyls. Presently, only three extant families survive, with several species threatened or endangered, especially rhinoceroses. Threats include poaching, habitat loss, and ecological changes, prompting ongoing conservation and captive-breeding programs.