Lagomorpha

Lagomorpha (Duplicidentata; infraclass Eutheria, cohort Glires) An order that comprises the families Eurymylidae (extinct forms), Ochotonidae (pikas), and Leporidae (rabbits, cottontails, and hares). The lagomorphs are believed to have diverged from a primitive eutherian stock at the same time as, or soon after, the rodents, so that similarities between lagomorphs and rodents may be very superficial. There is a single record from the late Palaeocene of Mongolia, but the order is not encountered again until the late Eocene, after which it spread widely in N. America and Eurasia. Ancestors of modern lagomorphs, very similar to modern forms, lived during the Oligocene. The incisors grow continually, but to either side of those of the upper jaw there is a small, peg-like incisor that gave the order its old name of Duplicidentata. There is a wide diastema between the incisors and the cheek teeth. The premolars and molars have sharp edges and are used for cutting rather than grinding, the upper teeth biting outside the lower teeth. The nostrils can be closed and are surrounded by naked skin which may be covered by surrounding fur. There are four or five digits on the hind limbs and five on the fore limbs. The tail is reduced and may not be visible externally. Like some rodents, lagomorphs pass food twice through the alimentary canal (caecotrophy).