Lagomorpha

The lagomorphs are the members of the taxonomic order Lagomorpha, of which there are two living families: the Leporidae (hares and rabbits) and the Ochotonidae (pikas). The name of the order is derived from the Ancient Greek lagos (λαγώς, 'hare') + morphē (μορφή, 'form'). There are about eighty-seven extant species of lagomorph, including about twenty-nine species of pika, twenty-eight species of rabbit and cottontail, and thirty species of hare. The nearest living relatives of lagomorphs are the rodents, together with which they form the clade Glires (Latin: 'dormice'). Early lagomorphs arose perhaps in Asia and spread across the northern hemisphere. Later, rodents came to dominate more environmental niches, and lagomorphs seem to have been in decline. Other names used for this order, now considered synonymous, include: Duplicidentata - Illiger, 1811; Leporida - Averianov, 1999; Neolagomorpha - Averianov, 1999; Ochotonida - Averianov, 1999; and Palarodentia - Haeckel, 1895. The extinct family Prolagidae is represented by a single species, the Sardinian pika Prolagus sardus, fossils of which are known from Sardinia, Corsica, and nearby small islands. It may have survived until about 1774. The evolutionary history of the lagomorphs is still not well understood. Until recently, it was generally agreed that Eurymylus, which lived in eastern Asia and dates back to the late Paleocene or early Eocene, was an ancestor of the lagomorphs. More recent examination of the fossil evidence suggests that the lagomorphs may have instead descended from Anagaloidea, also known as 'mimotonids', while Eurymylus was more closely related to rodents (although not a direct ancestor). The leporids first appeared in the late Eocene and rapidly spread throughout the Northern Hemisphere; they show a trend towards increasingly long hind limbs as the modern leaping gait developed. The pikas appeared somewhat later in the Oligocene of eastern Asia. Lagomorphs were certainly more diverse in the past than in the present, with around 75 genera and over 230 species represented in the fossil record and many more species in a single biome. This is evidence that lagomorph lineages are declining. Recent finds suggest an Indian origin for the clade, having possibly evolved in isolation when India was an island continent in the Paleocene. Lagomorphs are similar to other mammals in that they all have hair, four limbs (i.e., they are tetrapods), and mammary glands and are endotherms. They differ in that they have a mixture of 'primitive' and 'advanced' physical traits.