A grant has been awarded to Dr. Andre Wyss and Ms. Robin Whatley at the University of California, Santa Barbara to study the evolutionary history of a group of plant-eating reptiles that roamed the earth alongside the earliest dinosaurs and mammal ancestors. Commonly found in sediments spanning the Triassic Period (250 - 208 million years ago), these extinct reptiles, called rhynchosaurs, were long divided into three main sub-groups characterized by specific tooth types corresponding to the Early, Middle, and Late sub-divisions of the Triassic Period. Rhynchosaurs have thus been widely used to date Triassic fossil-bearing sediments, and to correlate faunas around the world. Recently, rhynchosaurs with dentitions and other skeletal features transitional between those assigned to Middle and Late Triassic ages have been found in Brazil, Argentina, and Madagascar. Several new features observed in the rhynchosaur from Madagascar have been noted in the literature, but never incorporated into studies of rhynchosaur relationships. Moreover, prior studies have not encompassed all rhynchosaurs, but instead have focused on representative Early, Middle, or Late forms. The primary goal of the proposed research is to construct a comprehensive evolutionary tree for rhynchosaurs from first-hand observation and measurement of all fossils belonging to this group, especially those from Brazil, Argentina, Africa and Madagascar. The rhynchosaur from Madagascar is of special interest, as it occurs in a recently discovered fauna with some of the earliest dinosaurs known worldwide. Whether this fauna is Middle or Late Triassic in age is very much open to question, an uncertainty stemming partly from the disputed identification of its rhynchosaur, Isalorhynchus. Comprehensive analysis of rhynchosaur relationships promises to clarify this ambiguity, and will lead to a better understanding of rhynchosaur evolutionary history. Results of this study will contribute to our understanding of Early Mesozoic vertebrate evolution, providing further biochronologic control for this important time of diversification in the fossil record.