Physical characteristics

The key characteristic of the lagomorphs, the one that led them to be classified originally in the duplicidentata, is the presence of a second peg-like upper incisor that nestles in behind the first large continually growing incisor. A third incisor forms, but is lost before birth or shortly thereafter. There is a single layer of enamel in the front incisors of rabbits in contrast to the double layer in rodents. This enamel layer surrounds the incisor on all sides (unlike in rodents) and is not colored by stored pigments, as are rodent incisors. The lower incisors in lagomorphs can occlude directly with the main upper incisors (as in rodents), but they can also "slide" behind the upper ones to press against their flat surface, thus allowing an efficient cropping mechanism. Canines are absent, and there is a gap (the diastema) between the incisors and the molars. The occlusal plane of the cheek teeth is not parallel with the zygomatic arch in lagomorphs, whereas this surface and the arch are parallel in rodents. The cheek teeth are rootless and hypsodont with two transverse ridges (unlike the several transverse ridges on rodent cheek teeth). Pikas have 26 teeth; leporids, 28. Lagomorphs have a fenestrated skull one with areas of thin lattice-like bones, a feature particularly well developed in some leporids.

Lagomorphs, especially the leporids, are quick on their feet and/or fast runners. Leporids have long legs and large hind feet, and the tibia and fibula are fused distally to add strength and reduce weight to the leg. The soles of lago-morph feet are covered with hair (except the distal-most toe pads in pikas). The hairs on the soles of the feet are rectangular when viewed in cross-section. The foot posture is digitigrade while running, but plantigrade during slow movements. No lagomorphs are able to grasp food with their paws. Ears are huge to relatively large (even pika ears are large for their body mass compared with most rodents), and tails are short and, in pikas, not visible. Lagomorphs have soft rather long fur, and the color is normally reddish to gray-brown. The gut is large, in particular the caecum, and all lagomorphs practice coprophagy (reingestion of feces). A pseudo-cloaca is present such that there is one opening for reproduction, urine and feces.

General body shape differs between representatives from the two families. Pikas are egg-shaped, roughly 5-8 in (13-20 cm) long, and weigh 3-10 oz (80-300 g). Leporids are more angular and larger, ranging in length from 10-30 in (25-75 cm) and in weight from 14 oz to 13.2 lb (0.4-6.0 kg).

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