Spinicaudatans from the Yixian Formation (Lower Cretaceous) and the Daohugou Beds (Jurassic) of Western Liaoning, China

摘要

The Jehol and Yanliao Biota constitute two world-famous Mesozoic lacustrine Konservat Lagerstatten. In contrast to numerous comparative studies on their different fossil assemblages, their taphonomic features have rarely been compared. Here we investigate the diagenetic pathways of spinicaudatans from the Lower Cretaceous Yixian Formation and the Jurassic Daohugou Beds to figure out whether they are similar. The specimens were categorized into eight types based on the colors of the carapaces and the characteristics of the surrounding matrix and subsequently were studied under the scanning electron microscope (SEM) and energy dispersive X-ray spectrometer (EDS). Spinicaudatan carapaces from the Yixian Formation are phosphatized lacking any traces of organic remains, whereas those from the Daohugou Beds contain a mineralized layer and a carbonaceous layer. Phosphatization apparently was a common taphonomic pathway of spinicaudatan carapaces in the Yixian Formation, while in the Daohugou Beds carbonaceous remains, probably the diagenetic products of chitin, are common. This suggests that the taphonomic environment and water chemistry, to which the Jehol and Yanliao Biota were subjected, differed. (C) 2019 Elsevier Ltd. All rights reserved.