Invertebrate paleontology with emphasis on lower Paleozoic faunas and stratigraphy. Current research includes early evolution of Brachiopoda and Cambrian development of the continental margins of the western United States and eastern Antarctica. Ohio State University, 1983. Current research includes Permian and Triassic permineralized plants from Antarctica and function and phylogenetic trends in fossil phloem. Ph.D., University of Illinois, 1964.
Current research includes plant-animal interactions, the origin of land plants, and symbioses.
Current research includes use of isotopic methods to investigage plants' response to the environment. Systematic biology and morphology of amphibians with emphases on osteology of anurans. Current research includes phylogeny of frogs including those known from the fossil record. Paleontology and paleoecology of the Upper Carboniferous and Permian invertebrates. Current research includes systematics and paleoecology of fossil chaetetid sponges.