Biogenic Structures Produced by Sand-Swimming Snakes: A Modern Analog for Interpreting Continental Ichnofossils

Abstract

Abstract A noichnological experiment using the Kenyan sand boa, Eryx colubrinus, reveals the diversity of biogenic structures produced by sand-swimming vertebrates in unconsolidated sand. Documentation of these biogenic structures will aid in the identification and interpretation of similar ichnofossils in the geologic record and help improve paleoenvironmental and paleoecological reconstructions. Two sand boas and three sand-filled chambers containing 1–3 cm thick layers of fine- to medium-grained sand were used in this burrowing experiment. The burrowing activities of the snakes were observed over a 14-day period and the chambers were photographed regularly to record sediment disturbance. Eryx colubrinus produced a number of biogenic structures including (1) cone-shaped, downward-tapering features; (2) straight, vertical tubes; (3) elongate, sinuous tunnels; (4) semicircular, concave divots; (5) downward- and upward-deflected laminae; and (6) offset laminae. These different trace morphologies are present together, forming a large compound ichnofossil resulting from locomotion, resting, and dwelling behaviors. Absent from the sand-swimming biogenic structures were active backfill features, open tunnels, and burrow linings. The recognition and interpretation of ichnofossils in the rock record of sand-swimming vertebrates requires their association with assemblages of known terrestrial body and trace fossils, rhizoliths, and pedogenic fabrics. Given the ecology of extant sand-swimming vertebrates, their biogenic structures characterize loose sediments with low interstitial moisture and environments with arid to semiarid climates. The biogenic structures produced in this experiment represent a new type of previously unrecognized biodiversity—that of sand-swimming vertebrates. In order to understand the evolution of fossorial behavior in continental vertebrates, recognition of the morphology of all types of interactions between vertebrates and the sediment must be considered.