Perissodactyls

Perissodactyla, commonly called the odd-toed ungulates, is an order of mammals that includes horses, rhinoceroses, and tapirs. A defining feature is the limb structure: the axis of the limb passes through the third toe (mesaxonic), and the number of weight-bearing toes is odd on the hind feet (for example, horses typically rely on a single prominent toe, while rhinos have three toes per foot and tapirs four on the front and three on the hind feet). They are herbivorous mammals that rely on hindgut fermentation, with relatively simple stomachs and a large cecum for microbial digestion.

The order comprises three living families: Equidae (horses, donkeys, zebras), Rhinocerotidae (rhinos), and Tapiridae (tapirs). Members occupy a range of habitats across Africa, Asia, and the Americas, from grasslands to forests and wetlands. Diet is primarily plant-based, with grazing or browsing adaptations in teeth and lips suited to their preferred vegetation.

Dentition and skull shape vary among lineages, reflecting different feeding strategies. Horses and other equids have high-crowned teeth adapted for grazing, rhinos possess large flat molars for grinding, and tapirs show teeth suited to a mixed diet. The fossil record shows Perissodactyla originated in the early to middle Eocene and once had a broader distribution and greater diversity, but numbers declined relative to artiodactyls in many regions.

Conservation concerns are prominent, as several species are threatened or endangered due to habitat loss, hunting, and fragmentation. Perissodactyls remain of interest for understanding ungulate evolution and the ecological roles of large herbivores.