Ecological data indicate that as the amount of precipitation in an arid areas increases, so too does mammalian taxonomic richness. This correspondence has been found in two late-Quaternary mammalian faunas from Utah, one from Homestead Cave in the Bonneville Basin. We use the remains of two species of woodrat (Neotoma cinerea and Neotoma lepida) from Homestead Cave to test the hypothesis that as the amount of precipitation in an arid area increases, so too does morphological diversity within individual mammalian taxa. Morphological diversity is measured as corrected coefficients of variation and as richness of size classes of mandibular alveolar lengths. Coefficients of variation for N. cinerea are few and coincide with moisture history if temporally successive small samples are lumped together. More abundant coefficients of variation for N. lepida coincide only loosely with moisture history, likely because such coefficients measure dispersion but not necessarily other aspects of variation. Richness of size classes of N. lepida is high during the early and late Holocene when moisture was high, and lowest during the middle Holocene when climate was most arid.

Certain species of the protozoan genus Besnoitia cause clinical disease in livestock and wildlife. In the present paper a new species, Besnoitia neotomofelis is described from the southern planes woodrat (Neotoma micropus). The parasite was detected by bioassay of woodrat tissues in outbred Swiss Webster mice in an attempt to isolate Toxoplasma gondii. Initially, the organism was misdiagnosed as T. gondii because it was highly pathogenic for mice and its tachyzoites resembled T. gondii tachyzoites. Further studies revealed that it differed structurally and biologically from T. gondii. Tachyzoites were successfully cultivated and maintained in vitro in bovine monocytes and African green monkey kidney cells, and in vivo in mice. Non-dividing, uninucleate tachyzoites were approximately 1×5 μm in size. Longitudinally-cut bradyzoites in tissue sections measured 1·5–1·6×7·7–9·3 μm. Tissue cysts were microscopic, up to 210 μm long, and were infective orally to mice. Cats fed tissue cysts shed unsporulated 13×14 μm sized oocysts. All mice inoculated with B. neotomofelis died of acute besnoitiosis, irrespective of the dose, and Norwegian rats became infected but remained asymptomatic. Entero-epithelial stages (schizonts, gamonts) were found in cats fed tissue cysts. Large (up to 40×50 μm) first-generation schizonts developed in the lamina propria of the small intestine of cats. A second generation of small sized (8 μm) schizonts containing 4–8 merozoites was detected in enterocytes of the small intestine. Gamonts and oocysts were seen in goblet cells of the small intestinal epithelium. Tachyzoites were present in mesenteric lymph nodes of cats. Phylogenetic analysis indicated that B. neotomofelis was related to other Besnoitia species from rodents, rabbits, and opossums. Besnoitia neotomofelis is distinct from the 3 other species of Besnoitia, B. wallacei, B. darlingi and B. oryctofelisi that utilize cats as a definitive host.