A possible pseudosuchian archosaur coprolite from the Middle Triassic lacustrine Ordos Basin, China: palaeobiological and palaeoecological significance

Coprolites provide valuable information for interpreting the feeding behaviours of producing animals and for deciphering trophic interactions within ancient ecosystems. Here, a newly found elongated coprolite with a cylindrical, J‑shaped morphology is described in detail from the Ladinian of the Ordos Basin, Shaanxi, China. It is interpreted to have been produced by a medium‑ to large sized reptile based on multiple lines of evidence including morphology, internal structure and inclusions. Three‑dimensional reconstructions of undigested food remains, imaged using microcomputed tomography (Micro‑CT), reveal that the reptile coprolite has fewer undigested inclusions than that of a shark coprolite from the same stratigraphic layer, suggesting a stronger digestive ability of its producer. The most probable producer is considered to be a pseudosuchian archosaur based upon its similarities with crocodilian coprolites previously recorded, evidence from neoichnology studies and the body fossil records of laterally correlatable strata. The Middle Triassic Ordos Basin was previously interpreted as the earliest known complex lacustrine ecosystem after the end‑ Permian mass extinction (EPME). The discovery enriches the diversity of the carnivorous predators, and refines the complexity of biotic interactions in this lacustrine ecosystem. A multileveled Mesozoic‑ type trophic network that displays complex predator‑ prey interactions among high‑ order trophic levels involving reptiles furthermore may suggest full recovery in the early Ladinian lacustrine ecosystem after the EPME.