The Oldest Known Example of Trilobite Ecdysis (Chengjiang Biota, Early Cambrian)  

Moulting is a requisite process in arthropod growth, but direct evidence of active ecdysis is rare in the fossil record.  Here we describe the trilobite Eoredlichia intermedia, from the Early Cambrian Chengjiang Biota of south China, in the act of moulting.  The more-or-less undisturbed ecdysial specimen is approximately 40 mm in length and shows the freshly moulted animal emerging at an angle from the old exoskeleton.  The shed librigenae are rotated counterclockwise through 180°. Five thoracic rings are visible on the new exoskeleton and eleven on the exuvium; adults of this species possess 15 thoracic segments.  The hypostome of the emergent animal is preserved in place, attached to the rostral plate.  The exoskeleton of the moulted trilobite is markedly different in colour from the exuvium, partly reflecting the lack of pervasive calcification.  The new specimen provides the first unequivocal evidence of moulting activity in trilobites during the Early Cambrian.