Ontogeny of the trilobite Estaingia sinensis (Chang) from the lower Cambrian of South China

New material collected from black shale of the lower Cambrian Shuijingtuo Formation in the Changyang County of Hubei Province, South China, allows a study on morphology and ontogeny of the trilobite Estaingia sinensis (Chang, 1953). Two protaspid stages can be defined on the basis of numerous well-preserved complete specimens, and subsequent ontogenetic stages are described largely based on the cranidia, which reveal prominent morphological changes such as the shortening of the frontal glabellar lobe, disappearance of the fixigenal spine and transformation of facial suture from proparian to opisthoparian.