John Bolt focuses on the early diversification of tetrapods, particularly amphibians, from the Mississippian, Pennsylvanian and Early Permian age (ca. 360 to 270 myr B.P.). The relationships and morphology of primitive amphibians from a new Mississippian locality in Southeastern Iowa constitutes one area of current research. Other studies examine the fossil evidence for the origin and evolution of the tetrapod auditory system and its implications for otic evolution and tetrapod relationships, and the origin and early evolution of the living amphibians (lissamphibians). Olivier Rieppel's primary research focus is the analysis of phylogenetic relationships of marine Mesozoic reptiles, specifically the Triassic stem-group, the Sauropterygia, from the northwestern United States, Europe, Israel and China. Related research addresses problems of skeleton formation in all three major clades of extant reptiles (lizards, crocodiles and turtles), focusing on patterns and sequences of ossification. He also conducts studies in the philosophy and methodology of systematics and its relation to evolutionary theory. Other Geology Department Research: Fossil Amphibians and Reptiles | Fossil Fishes | Fossil Invertebrates | Fossil Mammals | Fossil Plants | Meteorites | Paleontology