THE NEOICHNOLOGY OF VINEGAROONS

Neoichnological experiments with a giant vinegaroon—Mastigoproctus giganteus (Arachnida: Thelyphonida: Thelyphonidae) were conducted to evaluate the preservation potential of its trackways in different sedimentological and moisture conditions, and for comparison to similar trackways from in the fossil record. Trackways were investigated 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) to simulate soft ground, shifting sand conditions on a horizontal surface. Trackway production was video recorded, 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 track series exhibit a triangular pattern with the track of the second foot furthest from the midline, rather than a linear pattern described for trackways of other arthropods. Morphology of trackways reflects the hexapodous morphology of the animal similar to fossil trackways attributed to eurypterids. This relationship indicates that vinegaroons can be considered as modern locomotion analogs for eurypterids. No fossil trackway has been attributed to vinegaroons, so these trackways will serve as a model for assessment of fossil trackways. These trackways are assigned to the ichnogenus Hexapodichnus 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 such chelicerates as scorpions and spiders in dry, fine-grained conditions, but could be confused for the trackways of these other animals as preservation potential decreases. Vinegaroon trackways can be distinguished from similar trackways produced by other arthropods based on track morphology and the triangular shape of the track series arrangement.