The fossil record on Mesozoic mammals has expanded by orders of magnitude over the past quarter century. New specimens, some of them breathtakingly complete, have been found in nearly all parts of the globe at a rapid pace. Coupled with the application of new scientific approaches and techniques, these exciting discoveries have led to profound changes in our interpretation of early mammal history. Mesozoic mammals have come into their own as a rich source of information for evolutionary biology. Their record of episodic, successive radiations speaks to the pace and mode of evolutio.