Paleoethological Inference: Therapsids as a Model System

Abstract

Brent M. Graves (left) received the B.S. degree in Biology from Central Michigan University in 1981. He is currently working on an M.S. in Zoology at the University of Wyoming, and his thesis deals with the behavioral and physiological ecology of alarm pheromone communication in prairie rattlesnakes. Brent Graves' general interests include the evolution of animal communication, functional morphology, and behavioral physiology. He is the author of several research reports and reviews. David Duvall, (right), one of the guest editors of this issue, earned A.B., M.A., and Ph.D. degrees, from the University of California, Berkeley, San Jose State University, and the University of Colorado, Boulder, respectively. Upon completion of his Doctorate in Biology at Colorado in 1980, he accepted a position as Assistant Professor of Zoology at the University of Wyoming. Although thoroughly immersed in research in the areas of behavioral and physiological ecology, the evolution of animal communication, evolutionary biology, and herpetology, David Duvall is committed to and involved in biology education. Currently, he is the General Biology Coordinator at Wyoming (a program which handles about 1,500 students per year) and a current member of ABT's Editorial Advisory Board. He is the author of several research reports and reviews. Prior to the appearance of any dinosaur, the terrestrial fauna of the late Paleozoic was dominated by whose ancestors would one day be known as mammals. Classification of these reptiles into the orders Pelycosauria and Therapsida describes an evolutionary relationship, the latter animals being more advanced and grading directly into mammals. Ecologically, the mammal-like have been broadly grouped into herbivorous forms, exemplified by Lystrosaurus (fig. 1) and Styracocephalus (fig. 2), and carnivorous forms such as Trochosaurus (fig. 2) and Blattoidealestes (fig. 2). While both groups radiated evolutionarily under numerous circumstances, mammals are believed to have stemmed from a a carnivorous therapsid lineage. Paleontologists, those who study fossils, and biologists have come together to study such ancient animals forming the field of learning known as paleobiology. Central to the goals of paleobiology is elucidation of taxonomy and life histories and processes of ancient species, primarily through application of the principles of uniformitarianism, the comparative method, and inheritance relationships between fossil and living organisms. As a branch of paleobiology, paleoethology seeks to study the behavior of ancient animals by building inferential cases for hypothesized behavior patterns. Although such ancient behaviors can never be directly observed, indirect evidence can strongly support certain possibilities. Animals come to function effectively in their respective communities and habitats through the evolution of physiological, morphological, and behavioral adaptation. Knowledge of behavioral components of an animal's overall biology can aid in developing a clear understanding of how that organism lived and can help to discern evolutionary trends and processes. In studying biology today the relatively minuscule number of extant species available for study represents but a small portion of the species that have lived and shaped the current biosphere. Therefore, inferentially supported hypotheses about ancient animals can greatly increase our understanding of evolution and behavior.