Materials and Methods
We examined ABD specimens and associated primary and published documents of specimens that were previously referred to the lagomorph Lepus and the arvicoline taxa Lasiopodomys, Microtus, and Terricola. Data inconsistencies and their consequences are discussed below.
Institution and Field Collection Notation
Fossil specimens collected from the Anza-Borrego Desert and now curated at the Colorado Desert District Stout Research Center (SRC) comprise collections obtained under state permit by the Natural History Museum of Los Angeles County (LACM), the Imperial Valley College Museum (IVCM), and SRC staff and ABDSP Paleontology Society volunteers. All locality and specimen numbers originally assigned by those institutions are retained in the current ABDSP collection database, along with the parenthetical acronym for the collecting institution. The Park acronym is prefixed to the original collecting institution acronym for both the locality and specimen numbers, e.g., ABDSP(LACM), ABDSP(IVCM). The letter 'V' (signifying 'vertebrate fossil') is prefixed to the specimen number, to distinguish it from the locality number and from non-vertebrate fossils within the ABDSP system. Locality and specimen numbers separated by a forward slash, e.g., ABDSP(IVCM) 68123/V24828, indicate the association between a specimen and the locality where it was found. Specimen numbers published prior to consolidation of the collections appeared in the cited publications without 'ABDSP' or 'V' appended.
In our stratigraphic terminology 'VCFC section' refers to the sediments of the Vallecito Creek-Fish Creek Badlands in the southern part of the Park; 'Borrego Badlands section' refers to the sediments within the Borrego Badlands in the northern part of the Park; 'Anza-Borrego Desert' refers to the fossiliferous sediments of the entire Park, including the VCFC, Borrego Badlands, and other sections.
Additional institution and field collection abbreviations include GJM = George J. Miller field number; HJG = Harley J. Garbani field number; UADZ= Department of Zoology, University of Arizona (as published by
White 1984); UF = Florida Museum of Natural History, Vertebrate Paleontology (as published by
Primary documentation for the specimens reviewed here is on file at the Paleontology Section, SRC at ABDSP. Documents are either originals produced at IVCM and ABDSP or photocopies of original documents on file at LACM. Primary documents include field notebooks, field and master aerial photographs with localities pinpointed and labeled, locality catalogue cards, specimen catalogue cards, specimen tray labels, locality and specimen notes produced during the ongoing process of curation, letters of correspondence and database records for localities and specimens, including an unaltered 1994 copy of the LACM Anza-Borrego Desert specimen database records (1994 LACM database) obtained prior to the transfer of specimens to ABDSP.
The anteroposterior lengths of leporine p3s were measured using the orientation of White's (1991a:68) figure 2. Arvicoline m1s were measured along the occlusal surface, from the anterior to posterior edge. Tooth measurements were made through a dissecting microscope with a graduated reticle calibrated to 0.01 mm, and the tooth occlusal surface aligned parallel with the plane of the objective lens. The length of the leporine i–p3 diastema was measured with a 150 mm dial caliper calibrated to 0.01 mm.
All tooth images were drawn in Adobe Illustrator over digital photographs of the specimens. The accuracy of the outlines of the enamel, dentine, and cement features was verified by continuous comparison of the drawing, image, and direct observation of each specimen through the dissecting microscope. Examples of terms used in the text to describe leporine tooth morphology are illustrated in