Possibly the oldest fish-made resting traces

The Silurian Sharawra Member (middle to late Llandoverian) in Saudi Arabia exhibits unique surface traces with exceptional preservation: Seven small, wing-shaped structures occur on a sandstone slab showing well-defined hummocky cross-stratification having a few decimeters wavelength covered with a thin mud layer. These traces are preserved as concave epirelief along with elongated internal striae and surrounded with slightly elevated levees. Preservation of these delicate, 10-20 mm long and ~10 mm wide traces suggests that they were formed after a storm event when mud has already settled to the sediment surface. The lack of wave-generated sedimentary structures implies deposition between fair-weather and storm-wave base probably preventing further rapid reworking by waves. Based on their geometry, internal pattern and spatial distribution, these wing-shaped traces are interpreted to have been produced by relatively stationary bottom-feeding fish, morphologically similar to ancestors of Gobiidae, probably in the Actinopterygii class. The majority of fish-made trace fossils records feeding and locomotion behaviour, whereas the wing-shaped traces are interpreted to represent resting structures made by fish that pressed their fins downward on the muddy sediment surface and hence, represent undertracks. These structures are also possibly the oldest fish-made structures documented thus far. These wing-shaped traces are described as Pisquiesichnus dashtgardi igen. et isp. nov. in this study.