Aztlanolagus

REFERRED SPECIMENS DMNH 39054, 39057, 39061, 39066, 39067, 39071, 39072, 39075 , 39078, 39093, 39100, 39104, 39108, 39113, 39114, 39120, 39124, 39129, 39133, 39134, 39136, 39149, 39154, 39169, 39173, 39182, 3918639191, 39195, 39197, 39306, 39307, 39309, 39313, 39319, 39320, 39323, 39327, 39329, 39331, 39334, 39335, 39347, 39348, 39350, 39353, 39356, 39359, 39361, 39363-39366.

COMMENTS This genus is represented by remains that are significantly larger than those of the single described species, Aztlanolagus agilis (Russell and Harris, 1986). It is the most common leporid found in the Mark's Sink deposits but is very rare in DMNH 644. It is a small leporid, approximately the size of S. nuttallii, and it is found in association with both extant taxa, such as L. americanus and S. nuttallii, and extinct forms, such as Hypolagus spp. and Brachylagus coloradoensis (Ramos, 1999). Winkler and Tomida (1988) noted that Blan-can and Irvingtonian specimens of Aztlanolagus have less crenulation in their reentrants than do the younger specimens from the Wisconsinan. The Aztlanolagus material found at Porcupine Cave contains both the highly crenulated, though larger, specimens, and also less crenulated specimens, which are even larger. The latter appear in the lower parts of Mark's Sink.

BRACHYLAGUS

DESCRIPTION This genus is characterized by small size, a rudimentary tail, and the lack of an AR in the simplistic p3. The P2 has a single AR, a character unique among the living North American leporids. Only one living species is known, and it has short, rounded ears and very short hind legs. This genus was alternately considered part of Lepus and Sylvilagus before finally being separated out owing to its genetic and morphological differences.

GEOGRAPHIC DISTRIBUTION Two species are known, a living species found only in the Great Basin region and an extinct species recently described from central Colorado.

table 15.1

Matrix of Species Presence and Absence for the Horizons of the Main Dig Site in the Velvet Room

Brachylagus coloradoensis ________

note: present; *, tentative identification.

note: present; *, tentative identification.

FIGURE 15.2 Temporal range of species identified in the DMNH Velvet Room sites. EIrv/Lblancan, early Irvingtonian / late Blancan boundary. The 780 Ka calibration is the Brunhes-Matuyama boundary.

TEMPORAL DISTRIBUTION Species of Brachylagus are known from the Irvingtonian of eastern Nevada (C.J. Bell, pers. comm.) and the early Irvingtonian of central Colorado (Ramos, 1999).

BRACHYLAGUS COLORADOENSIS RAMOS, 1999

REFERRED SPECIMENS DMNH 28901, 33250, 33255, 33257, 33260, 33261, 33270-33272, 39062, 39079, 39109, 39116, 39117, 39121-39123, 39144, 39147, 39161, 39176, 39305, 39315, 39316. See also Ramos (1999).

COMMENTS This is a small leporid, only slightly more robust than the extant species, Brachylagus idahoensis. The p3 is simple, with a PER extending one-half to two-thirds of the way across the width of the tooth. A slight posterior internal reentrant (PIR) is often present, but there is no AR. The P2 has a single AR as in Hypolagus. The initial excavators of the Pit identified the remains as B. idahoensis (Barnosky and Rasmus-sen, 1988); however, the dental differences are significant, and these fossils are now allocated to a new species of Brachy-lagus (Ramos, 1999).

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