Leporidae—Hares and Rabbits // Ochotonidae—Pikas
The Lagomorpha consists of only two living families, the Ochotonidae (pikas) and the Leporidae (hares and rabbits). Although at one time considered as one of two major divisions of rodents (the Duplicidentata), it eventually was realized that, despite some features in common, the two orders have had long separate evolutionary histories. All lagomorphs are herbivores, which has shaped features of skull and dentition. Characteristics shared by rodents and lagomorphs include ever-growing incisors and a diastema (space) separating the incisors from the cheek teeth. A major difference, however, is that no rodent has more than a total of two upper and two lower incisors, whereas lagomorphs have a total of four upper incisors. I2, however, lies in back of I1, hidden from an anterior viewpoint. Figure 1 shows a typical lagomorph skull; the small pegs behind the front incisors are the I2s. Another characteristic of lagomorphs is fenestration of portions of the skull. These areas are apparent in the figure as open networks of bone (in the view seen in the figure, in the rostral area and anterior to the auditory bulla).
Fig. 1. Skull and mandibles of the Desert Cottontail (Sylvilagus audubonii).
In the Southwest, American Pikas currently are high altitude animals, living near or above timberline. New Mexico, Arizona, and Mexico lack Pleistocene records; however, they are known from the Great Basin.
The Leporidae is well represented in Pleistocene fossil cave faunas and are not uncommon in some open sites. Although a successful group, they show little morphological variability. A person using Fig. 1 could instantly identify any of the species of Pleistocene and modern lagomorphs as a lagomorph (and with minor coaching, as a leporid). All of our representatives share the same dental formula: 2/1 0/0 3/2 3/3, all teeth are unrooted and hypselodont, all upper first incisors are grooved, etc. Because of this uniformity, identification to species becomes a challenge, every species looking very much as any other species. As a result, many faunas have "Lepus sp." and "Sylvilagus sp.", but nothing identified to species.
Last Update: 12 Feb 2014