First report of oribatid mite (arthropod) borings and coprolites in Permian woods from the Helan Mountains of northern China

Oribatid mite borings and coprolites are described for the first time from the Permian of the northern Helan Mountains, in the Inner Mongolia (Nei Mongol) and Ningxia Huizu Autonomous Regions, northern China. To our knowledge, they are the first reported mite borings and coprolites from the Cathaysian Palaeozoic. They occur in petrified gymnospermous woods from five stratigraphic horizons within three formations: the Cisuralian Shanxi, Guadalupian Lower Shihhotse and the Lopingian Sunjiagou Formations. The borings and galleries are interpreted as trunk tunnels and their secondary branches, which are interconnected to form a complicated maze-like network. Two kinds of coprolite can be recognized based on their dimensions, shape and density of composition. One form is about 20–65 µm in diameter and of spheroidal shape, whereas the other is about 37.5–70 µm × 55–145 µm and ovoid in shape. The smaller form of coprolite is densely compacted and occurs in all five horizons. The larger form shows a fairly loosely organized texture and occurs only in the Cisuralian age wood. This report of Palaeozoic wood-borers and their coprolites from the Cathaysian flora is consistent with previous data on the palaeogeographical distribution and stratigraphic occurrences of plant–arthropod interactions.