6-5 Using Avian Neoichnology to Inform Reconstructions of Ancient Lacustrine Ecosystems of the Jurassic Moenave Formation in Southern Utah

Session: Advances in ichnology: walking in Memphis and other records of behavior

Presenting Author:

Authors:

Abstract:

The St. George Dinosaur Discovery Site at Johnson Farm in southern Utah provides exceptional insight into an early Jurassic lake ecosystem filled with a variety of body and trace fossils including dinosaur tracks that represent such diverse locomotion behaviors as walking, running, crouching, and swimming. Tracks are preserved in situ and can therefore offer more detailed information about ancient environments than body fossils alone. Tracks produced by different locomotion behaviors have unique quantifiable properties that may further enhance environmental interpretations. Our neoichnological experiments conducted at a poultry farm in northern Mississippi involve domestic chickens (Gallus gallus domesticus) and domestic turkeys (Meleagris gallopavo domesticus) as modern analogs for track production under different substrate conditions. The focus of our neoichnological experiments is to recognize how the depth of standing water and substrate compaction affect track preservation. 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, sediment under swim tracks should exhibit lower bulk density, whereas the sediment below terrestrial walking tracks should have greater bulk density because more weight was applied during the creation of the tracks. In our trackmaking trials, we collect sediment samples of known volume from within tracks and from undisturbed sediment directly adjacent to tracks. Mass and moisture content are measured for each track in the lab. Tracemaker masses ranged between 1.8 and 6.6 kg. Trampled sediment had a mean moisture content of 21.1% and ranged from 12.6 to 42.7%. Undisturbed sediment had a mean moisture content of 20.5% and ranged from 12.6 to 46.1%. Dry bulk density data were essentially the same for trampled and undisturbed sediment, with a mean of 1.5 g/cc and a range of 1.2 to 1.6 g/cc. Paired t-tests showed no significant differences with the current dataset. More data will be collected this spring to create a larger and more robust sample size. Future field work at the SGDS will include the use of LiDAR to create high precision, three-dimensional models of a sample of excavated swim track blocks. Using LiDAR in conjunction with neoichnological experiments, we aim to reconstruct Moenave Formation paleoenvironment and substrate conditions in order to better understand the preservation of rare dinosaur swim tracks.

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