Aztlanolagus agilis Russell and Harris, 1986

Christopher, Jass, N., Usa, J. J. & Usa, 2009, Pleistocene lagomorphs from Cathedral Cave, Nevada, PaleoBios 29 (1), pp. 1-12 : 3-4

Aztlanolagus agilis Russell and Harris, 1986

Referred Specimens —See Appendix 1.

Description —The p3s of Aztlanolagus agilis are characterized by the presence of five reentrant folds ( Fig. 4a; Russell and Harris 1986). No extant North American leporid retains this pattern, and among fossil taxa only Nekrolagus is similar ( Russell and Harris 1986). All specimens identified as A. agilis exhibit a strongly developed anterointernal fold and a well-developed posterointernal fold ( Fig. 4b) or lake. The presence of a strongly developed anterointernal fold on the p3 distinguishes A. agilis from Nekrolagus , in which the fold is less developed or absent ( Russell and Harris 1986). The degree of crenulation within individual folds varies among individual specimens from Cathedral Cave. Table 1 summarizes the number of major crenulations in the anteroexternal reentrant, along the posterior wall of the posterointernal reentrant, and along the posterior wall of the posteroexternal reentrant. For specimens of A. agilis from Cathedral Cave, the p3 average length is 2.40 mm (n = 25; SD = 0.23; range = 1.7–2.8) and average width is 2.29 mm (n = 25; SD = 0.34; range = 1.2–2.8). These are slightly larger than average measurements recorded by Winkler and Tomida (1988) for other localities in the southwestern United States.

Discussion— Aztlanolagus is known from Blancan to late Rancholabrean deposits in the western United States and Mexico. Records other than Cathedral Cave come from localities within Porcupine Cave, CO ( Barnosky and Hopkins 2004, Baxter 2004), and localities in northern Mexico, New Mexico, Arizona, and Texas ( Russell and Harris 1986, Winkler and Tomida 1988). Although Winkler and Tomida (1988) tentatively referred all specimens that they examined to A. agilis, Baxter (2004) reported Porcupine Cave specimens as Aztlanolagus spp. because of variation in tooth size and crenulation patterns.

Aztlanolagus might be synonymous with Pliopentalagus , an extinct leporid known mostly from China that has five reentrant folds on the p3 ( Tomida and Jin 2002, 2004). However, until the argument for synonymy is formalized, Aztlanolagus should be retained. Taxonomic issues notwithstanding, the disappearance of A. agilis is one of the few known late Quaternary small mammal extinctions in continental North America.

The records of Aztlanolagus agilis from Cathedral Cave presented here represent its first known occurrence in the Great Basin. The only other specimen known from the Great Basin is unnumbered in bulk material from Smith Creek Cave , Nevada, housed at the Nevada State Museum (Jass personal observation) .