IDENTIFICATION OF BIOGENIC STRUCTURES PRODUCED BY TERRESTRIAL SALAMANDERS USING MODERN ANALOGS

Body fossils of modern salamanders (Amphibia: Caudata) have a fossil record that extends to the Jurassic while the record of terrestrial, fossorial amphibians extends into the Early Carboniferous. The absence of an abundant trace fossil record is likely due to the misinterpretation of trace fossils which should be attributed to amphibians resulting from the rarity of studies describing the biogenic structures produced by extant salamanders and other amphibians. In this project, two species of common burrowing salamanders, Ambystoma tigrinum and Ambystoma opacum, were used to investigate the burrow morphologies produced by amphibians and to determine the connections between burrow morphology and environmental conditions. Individual specimens were placed into 10, 30, and 65 gallon sediment-filled aquaria and allowed to burrow for periods of up to two weeks in stable temperatures of 18-20˚C. The sediment was composed of 75% coconut fiber and 25% soil with sediment moisture levels averaging 74%. The salamanders were then exposed to variations in both soil composition and soil moisture for two week intervals. Sediment density was increased with the addition of soil and decreased through the addition of fine-grained sand to the sediment. Soil moisture percentages were both increased and decreased by 20%. Changes in the salamander’s behavior while burrowing and changes in biogenic structure morphology in response to environmental changes were observed. Open burrows were cast and described. Descriptions of each structure included general architecture, dimensions, bioglyphs, complexity, and tortuosity. Both A. opacum and A. tigrinum burrowed by compaction, using their heads and their limbs to force themselves into the substrate. Structures produced by A. opacum consisted of simple shafts, elliptical in cross section, often terminating in a single chamber and entering the substrate at angles of 38º-64º. Specimens of A. tigrinum produced similar simple burrows terminating in a chamber and more complex U-shaped and W-shaped burrows, also elliptical in cross section which entered the substrate at angles of 12º-86º. Data obtained from this study will be useful in improving the identification of continental ichnofossils and in the development of better paleoenvironmental and paleoecological reconstructions.