The evolutionary transition from reptiles to mammals took place during the Triassic Period, and higher vertebrate fossils of this age are studied intensively. Dr. A.W. Crompton has the unprecedented opportunity to study Triassic fossils of early mammals and mammal-like reptiles from the People's Republic of China. The specimens will be taken on loan to Harvard University where closely-spaced sections through the skulls will be cut and recorded on a computer-based image analysis system. The sections will be integrated by the computer into a three- dimensional reconstruction, revealing new morphological features of the cranial interiors. The data to be gathered during this study will have direct impact on the several competing hypotheses that seek to explain the origin (or origins) of mammals from reptiles. Evolutionary biologist, vertebrate anatomists, and paleontologists will find the results of this study of interest. The project will also improve scientific collaboration and exchange between the U.S. and China.