Biogenic structures of modern and fossil continental organisms: Using trace fossil morphology to interpret paleoenvironment, paleoecology, and paleoclimate

This study examines the paleoenvironmental, paleoecological, and paleoclimatic significance of the biogenic structures of continental, terrestrial organisms. The combination of paleontological, paleopedological, and ichnological methods provides a more comprehensive understanding of the effects of environmental and climatic change on the composition and behavior of the soil fauna.; Neoichnological experiments using fossorial reptiles permits the documentation of previously undescribed trace morphologies and their associated behaviors. By studying the morphology of the biogenic structures of known organisms, ichnologic signatures may be recognized and attributed to specific taxonomic groups and behaviors. The variations in architectural and surficial morphology are also related to changes in substrate composition and soil moisture and therefore are useful in paleoenvironmental reconstructions.; Field work in Permian and Eocene-Oligocene paleosol-bearing units is used to study the responses of continental burrowing organisms to local and global environmental changes. Amphibian aestivation burrows in Permian pond deposits indicate an adaptation toward the seasonally arid climates that developed in the North American midcontinent during the late Paleozoic. Invertebrate and vertebrate ichnofossils from the White River Formation spanning the Eocene-Oligocene global cooling event, however, show no obvious response to climate change. Instead they respond to basin-scale autogenic sedimentologic and hydrologic processes.; Phylogenetic and paleobiogeographic analyses of amphisbaenians provide insight into the evolutionary history of vertebrate soil fauna. Paleobiogeographic analyses using a modified Brook's Parsimony Analysis shows that speciation within the Amphisbaenia is through geodispersal and vicariance. This result suggests that although amphisbaenians are entirely fossorial, they are capable of moving across large geographic areas. A species-level phylogenetic analysis of fossil amphisbaenians in North America reveals also that individual species of these reptiles may remain stable for up to 8 my.; Ichnologic and paleontologic evidence suggests that the maintenance of microenvironments within the soil provides fossorial organisms protection from environmental and climatic changes on the surface. Changes in the behavior and composition of the soil fauna, therefore, require extreme environmental and climatic changes over long periods of time. Experimental work with extant fossorial organisms, however, can provide ichnologic signatures that may indicate more subtle shifts in behavior due to surface and subsurface environmental perturbations.