Mammals arose early in the Mesozoic Era, roughly 200 million years ago, and remained at low diversity until near the end of the Cretaceous Period, about 60 million years ago. Study of the fossil record of Mesozoic mammals has been concentrated in certain regions, and remains poorly known from other areas with promising Mesozoic deposits. Dr. Richard Cifelli has recovered and studied Cretaceous mammals of southern Utah, a region from which fossil mammals were not previously known. His efforts have produced sizeable collections of microvertebrate fossils, and a microcomputer database of the collections. Dr. Cifelli proposes to complete field collections from this area and curate and describe the fossil mammals from the region. This research project will expand significantly our understanding of mammalian diversity and evolution prior to their rapid diversification at the close of the Mesozoic Era. The collections, database, and descriptions of species will provide the foundation for future studies of function, evolution, and biogeography, subjects that will be of interest to a wide variety of paleontologists and evolutionary biologists.