Alilepus—Alilepus Rabbits // Aluralagus—Virginia Rabbit // Aztlanolagus—Aztlán Rabbit // Brachylagus—Pygmy Rabbit // Hypolagus—Hypolagus Rabbits // Lepus—Jackrabbits // Sylvilagus—Cottontails
Leporids, of course, have the ordinal characteristics noted under Lagomorpha. To recapitulate briefly, the presence of peg-like second incisors directly behind the grooved upper first incisors is unique to the order. The tooth formula of regional leporids is 2/1 0/0 3/2 3/3 = 28. There is a major diastema separating the incisors from the cheek teeth. All teeth are hypselodont, and cheek teeth are lophodont (typical upper and lower cheek teeth are shown in Figs. 1 and 2). The distal portion of the fibula is fused to the tibia. The skull, and to a lesser degree, the dentary, displays fenestrated areas. Although skeletal features are easily recognizable as being lagomorph, differences between species usually are subtle.
Fig. 1 (left). Upper right M1-2 of Sylvilagus. The reentrant loop of crinkled enamel extends most of the way across the tooth and is filled with cement. Fig. 2 (right). Lower right p3-m2 of a cottontail (Sylvilagus). The trigonid of a tooth is separated from the talonid by a cement-filled medial lateral reentrant extending almost entirely across the tooth. Figures are to different scales.
Seven genera of Pleistocene leporids occur in our region. The late Blancan genera require teeth, usually p3, for identification. Size is useful for most late Wisconsin genera. With exceptions, Lepus often can be separated from the other genera by larger size. On complete skull material, Lepus can be told from Sylvilagus by the interparietal bone of the skull being fused whereas it's unfused in Sylvilagus (Fig. 3). Since this portion of the skull is seldom preserved, this feature is of little use in paleontology.
Fig. 3. Comparison of the jackrabbit interparietal area (left) with that of a cottontail (right). The sutures have been enhanced for easy discrimination. The suture between the supraoccipital and the parietal/interparietal area is seen on both. The depressed, fenestrated area (INT) anterior to the supraoccipital in the jackrabbit is approximately the equivalent of the interparietal seen in the cottontail, but not separated in the adult from the parietal by a suture as it is in the cottontail.
Aztlanolagus is a small rabbit whose adult post-cranial skeleton is apt to be confused only with that of the Pygmy Rabbit (Brachylagus). The lower cheekteeth are recognizably different from other Pleistocene taxa. Brachylagus differs from Lepus and Sylvilagus in that P2 has a single anterior reentrant rather than three (the upper dentition of Aztlanolagus has not been definitely identified). For other differences, see the species accounts.
Last Update: 10 Mar 2013