Moulting behaviour of the Ptychopariid trilobite Xingrenaspis xingrenensis from the Cambrian Kaili Formation in Jianhe, Guizhou
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Abstract:
Abundant, well-preserved moulted ones (ecdyses) of ptychopariid trilobite Xingrenaspis xingrenensis found from the Cam-brian Miaolingian Series, Wuliuan Stage Kaili Formation (middle and upper part) in eastern Guizhou, provide substantial material for revealing the moulting behavior of this trilobite lineage. Comparative analysis on 106 disarticulated exoskeletons of Xingrenaspis xingrenensis reveals that the preservation types can be divided into the following 3 styles: Style I (63 pieces): axial shield, the librigenal and ventral structure of the cephalon are displaced, while the cranidium, thorax and pygidium are mostly connected; Style Ⅱ (2 pieces): The thorax and pygidium connected, the cephalon is disconnected from the cephalothoracic joint and turned back 180°, the librigenal and the ventral structure of the cephalon are missing or pressed under the thorax; Style Ⅲ (41 pieces): The cranidium and thoracopygon are connected, and the librigenal area detached around the trilobite or pressed under the thorax. Based on these 3 preservation types, it was found that the moulting method ofXingrenaspis xingrenensis is not only carried out through the anterior exuvial gape created by the operation of the cephalic sutures, but also had the frac-ture at the joint of the cephalothoracic to complete the moulting behavior. Taphonomically, the preservation of distinguishing skeletal assemblage presumed to be resulted from moulting must be buried in a hydrostatic depositional environment, and the discovery of a large number of shedded exoskeletons of Xingrenaspis xingrenensis provides critical evidence for the in-situ (near-in-situ) burial of the Kaili Biota.
