NEOICHNOLOGICAL STUDY OF TURTLE STERNOTHERUS ODERATUS TRACKWAYS

This study examines the effects of moisture and grain size on trackways made by the common musk turtle in various media. Sediment was collected from the Kansas River and sieved to yield very fine, fine, and medium sand. After sieving, the sand contained approximately 10% clay. The sand was poured in a 100 cm by 30 cm container to a depth of 3-4 cm, and then smoothed with a straight edge. A musk turtle made trackways in each sand size while dry, moist, and saturated. The moisture was added after the media surface was smoothed. The percent water weight was calculated using the initial wet weight of the sediment and the weight after being oven dried for at least 24 hours. The percent water weight for the very fine, fine, and moist sands were 19.25, 6.67, and 11.89, respectively. The percent water weight for the fully saturated very fine-, fine-, and medium-grained sands were 23.85, 18.55, and 16.74, respectively. The trackways were then cast using dental cement. Results from the trackways and casts indicate dryer, finer sands and saturated coarser sands yield the most detailed trackways. Dry and fully saturated conditions yield similar trackway results, and moist sediment yields only claw marks, which are least likely to be preserved in the fossil record. Posterior plastron drag marks can be seen in trackways in very fine and fine dry sand and in medium saturated sand. Tail drag marks can be seen in very fine dry conditions. The detail in the trackways was well preserved in the casts. The preservation potential of very fine dry sediment, however, is very low. The preservation potential of saturated coarse sediment is much higher. This study included variations in media to provide modern trackways to help interpret ancient trackways and the paleoenvironmental conditions in which ancient trackways were produced. The trackways in this study were produced on level surfaces; therefore possible differences in morphologies as a result of inclined surfaces should be taken into consideration when comparing with the fossil record.