BIRD BATHS: NEOICHNOLOGICAL EXPERIMENTS WITH AVIANS TO INVESTIGATE THE EFFECTS OF VARYING WATER LEVELS ON BEHAVIOR AND RESULTING TRACK PROPERTIES

Tracks are the product of the interaction between the locomotion behavior of an animal and a sedimentary substrate. It is therefore imperative to evaluate the contributions of both the behavior represented and the consistency of the sediment, especially when trying to interpret fossil vertebrate tracks. Many previous studies have shown that track types representing different locomotion behaviors—such as running, walking, and swimming—have unique quantifiable properties. Theropod dinosaur tracks have received particular attention because extant birds can be used as neoichnological analogs. Building upon previous work, we aim to use neoichnological experiments with birds to enhance interpretations of substrate and paleoenvironment from fossil theropod tracks. Ongoing neoichnological experiments with domestic chickens (Gallus gallus domesticus) are being used as modern analogs for track production under different substrate conditions. We are working with chickens because the morphology of their feet (three forward-facing clawed digits and reduced digit I) closely resembles bipedal, non-avian theropod dinosaur feet morphology and therefore will likely produce similar tracks. Notably, our trials will consider the role of depth of standing water and substrate compaction in the experimental setup. Preliminary results show that chicken tracks made in subaerially exposed sand have significantly lower total divarication angles and significantly greater digit IV lengths than tracks made under subaqueous conditions. Planned research will involve water levels deep enough to support the trackmaker’s body, requiring kicking off of the substrate to model “swim” tracks. If this proves difficult or stressful for the chickens, we will use domestic ducks (Anas platyrhynchos domesticus).

We hypothesize that there is a relationship between locomotion-induced sediment compaction—as measured by bulk density—and the degree to which the trackmaker’s body is buoyed by water. Accordingly, the sediment under swim tracks should exhibit lower bulk density, whereas the sediment below terrestrial walking tracks should have greater bulk density. This could then be applied to fossil tracks by using thin sections to evaluate porosity of the lithified substrate below the tracks versus the porosity of a control nonbioturbated lithified substrate.