A Keichousaurus-bearing regurgitalite from the Middle Triassic Xingyi Fauna, Dingxiao of Xingyi City, Guizhou, South China

Bromalites (coprolites, regurgitalites and consumulites) are trace fossils that preserve valuable information on their producers’ diet and feeding behaviors. Here, we report a compact skeletal mass from the Middle Triassic Xingyi Fauna of Dingxiao, Xingyi City, Guizhou Province, South China through multiple analytical methods. Using micro-CT scans, we provide 3D reconstruction of two vertebral arches, four coracoids, three ribs of three kinds, four humeri including one male and three female ones, five scapulae including two right one and three left ones of different sizes, which are inferred to be from at least three individuals of Keichousaurus hui. Bone aggregates of multiple individuals, associated with less gastric etching on bone surfaces and the absence of a phosphatic and organic matrix surrounding the bones as revealed by microstructural and chemical analysis respectively, suggest that this bone mass is a regurgitalite rather than a coprolite. The vertebrate fossils reported from the regurgitalite-bearing strata suggest that the best candidate for the potential producer of the regurgitalite are the near-shore sauropterygians Nothosaurus or Lariosaurus. The discovery of a Keichousaurus-bearing regurgitalite shed new insights on the feeding behaviors of Middle Triassic marine reptiles and the paleoecology of the Xingyi Fauna.