METHODS AND MATERIALS

All of the small mammals (about 2,500 identifiable specimens) collected from the Panaca Fm. were identified by the author and compared with the small mammals collected from the Panaca Fm. by Galusha and Emry for the AMNH. All specimens included here in materials examined are from the UALP collection unless indicated otherwise.

Most of the identified small mammals are isolated teeth that were picked from fine or coarse concentrate after multiple washings of sediment in screen boxes. Specimens were mounted (using polyvinyl acetate dissolved in acetone) on the head of a half-inch straight pin embedded into a small cork, to facilitate handling and measurement; a half-dram glass vial was placed over the pin for safety in storage. Measurements were made to the nearest 0.01 mm with the aid of a reticule mounted in a microscope. All measurements are maximum dimensions, regardless of wear. Transverse dimensions are perpendicular to anteroposterior dimensions. When applicable, the means, standard deviations and coefficients of variance were computed for each sample. Upper teeth are abbreviated with capital letters (e.g., M1), and lower teeth are abbreviated with lower case letters (e.g., m1).

Five stages of tooth wear were used: young—crown not worn, roots not yet developed; slightly worn—crown slightly worn, roots developed but short; moderately worn—crown worn down about halfway, roots long but not closed; worn—crown worn down more than halfway, roots closed; well worn—crown almost worn out, roots closed.

In this study, 24 teeth from different localities within the formation were examined for their schmelzmuster. The teeth were embedded in epoxy resin and ground with coarse and fine silicon-carbide abrasives. The grinding surface was parallel to the occlusal surface throughout the entire grinding and polishing procedure. After polishing, the exposed enamel surface was etched in 5% HCL for 15-20 seconds. All of the specimens were then coated and examined under the scanning electronic microscope (SEM).

Institutional abbreviations: American Museum of Natural History (AMNH), Frick Laboratory of American Museum of Natural History (F:AM), University of Kansas (KU), San Bernardino County Museum (SBDM), University of Arizona Laboratory of Paleontology (UALP), University of Michigan Museum of Paleontology (UMMP), U.S. Geological Survey (USGS). Locality data are available to qualified researchers from the Department of Geosciences, University of Arizona, which is the repository for all UALP specimens. In the Materials examined sections, the acronym UALP has been removed to save space.