THE IDENTIFICATION AND INTERPRETATION OF FOSSORIAL REPTILE ICHNOFOSSILS THROUGH ACTUALISTIC STUDIES

Experimental work with modern burrowing organisms is necessary to interpret the diverse ichnofossils preserved in the continental rock record. The objective of this study is to observe and describe the morphology and associated behaviors of biogenic structures produced by extant fossorial reptiles in order to facilitate the recognition of these structures in the fossil record. In addition, this study investigates the physiological and behavioral responses of fossorial reptiles to variations in soil composition and moisture. Studying these organisms under variable environmental conditions allows morphological comparisons of modern and ancient biogenic structures to be made for more accurate interpretations of paleoenvironmental, paleohydrologic, and paleoclimatic conditions.

Burrowing experiments were conducted with the Kenyan sand boa Eryx colubrinus and the amphisbaenian Amphisbaena camurea. The experiments were performed in sand- and soil-filled aquaria under controlled temperature and moisture conditions. The biogenic structures of the sand boas produced in dry sand consisted of two-dimensional sediment deformation structures morphologically similar to the ichnotaxa Arenicolites, Asterosoma, Bergaueria, Conichnus, Phycodes, Planolites, Skolithos, and Teichichnus. Biogenic structures of the amphisbaenians produced in clay-rich substrates consisted of complex three-dimensional networks of branching tunnels similar to yet distinct from Thalassinoides. Amphisbaenian traces produced in sandy substrates were dominated by soft sediment deformation features and isolated, open burrows similar to Planolites and Palaeophycus.

A diverse number of biogenic structures are produced by fossorial reptiles. These structures are characterized by distinct architectural and surficial morphologies that may be used to identify them in the fossil record. Since the same taphonomic biases to which body fossils are subject typically do not affect body fossils, knowledge of the morphology of reptile ichnofossils may lead to the extension of the stratigraphic and geographic ranges of many groups of these animals. The variation in reptile burrow morphology with changes in substrate composition and moisture may also provide insight into the different soil environments that they inhabited.