Neoichnological Experiments with Vinegaroons and Implications for Recognition of Depositional Environments
Neoichnological experiments with a vinegaroon (Thelyphonida: Thelyphonidae) were conducted to evaluate the preservation potential of its trackways in different sedimentological and moisture conditions and to compare them to similar trackways found in the fossil record. Trackways were produced under nine experimentally controlled variations of sediment size (fine-, medium-, or coarse-grained sand) and moisture added to sediment surface (0 mL, 5 mL, or 10 mL). All combinations of sediment size and moisture content were designed to simulate soft ground, shifting sand conditions on a horizontal surface. Trackways were video recorded during trackway production, photographed and cast in plaster. Individual tracks were oblong to striate, with the first and third foot on each side of the animal producing a striation parallel to the direction of motion and the second foot producing a striation perpendicular to the direction of motion. Video evidence from track production indicates that track associations exhibit a triangular pattern with the track of the second foot furthest from the median of the trackway, rather than a linear pattern as described for trackways of other arthropods, such as scorpions. Morphology of trackways is reflective of the hexapodous morphology of the animal and is similar to fossil trackways attributed to eurypterids, indicating that vinegaroons can be considered as modern locomotion analogs for that extinct group. No fossil trackway has been attributed to vinegaroons, so these trackways may serve as a model for assessment of fossil trackways. These trackways are best assigned to the ichnogenus Hexapodichnus or Lithographus based on the striate track pattern and triplet track arrangement. Preservation potential decreased as a function of increasing moisture content and sediment grain size, with tracks becoming less oblong and more rounded before ultimately becoming unpreserved. Trackways produced by vinegaroons are distinct from the trackways of other chelicerates, such as scorpions and spiders, in dry, fine-grained conditions, but could be confused for the trackways of these other animals as preservation potential decreases.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009