Lizards (nonophidian squamates) from a vertical series of localities in the early Eocene Wasatch Formation (Washakie Basin, Wyoming, USA) deposited during an interval of global warming are described on the basis of isolated cranial and some postcranial bones. At least 24 species are present. New material supports a close relationship of the iguanid Paranolis to Anolis (to the exclusion of Anolbanolis). Records of Tinosaurus and Scincoideus are the earliest in North America; a potential affinity of the latter, a new species, with Lacertidae is explored. A new species of Palaeoxan tusia and two species related to Neotropical Night Lizards, Lepidophyma, are named. A rhineurid amphisbaenian is present. New material of Apodosauriscus minutus further bolsters the case for its relationship to living Anniella. Glyptosaurine anguids are also present, including new species referred to Xestops, Arpadosaurus, and Glyptosaurus, the last with distinctive crushing posterior teeth. A distinctive new anguimorph lineage, Entomophontes, may be related to Xenosaurus. Considerable cranial material is referred to a new species of Provaranosaurus; we argue that this lineage is closely related to extant Shinisaurus. Restes-like remains are smaller and rare. Helodermatidae is represented by a single osteoderm. The varanid Saniwa is present. The four localities examined here record an interval of warming in the Rocky Mountain interior, when temperatures rose toward their Cenozoic acme in the Eocene Climatic Optimum. Faunal composition shows only two major deviations at a higher taxonomic level, suggesting a prevailing stability. Maximal within-locality species diversity (richness), based on cranial material (18 species), is seen at the top of the section. The diversity difference between the upper and lower part of the section is statistically significant. There is an underlying component of noise to the diversity data with regard to rarer taxa. Diversity changes primarily as a result of dispersal on a local level.
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