Study On The Ontogeny Of Eodiscoid Trilobites Tsunyidiscus Acutus And Sinodiscus Changyangensis From The Shuijingtuo Formation, Lower Cambrian In Eastern Yangtze Gorge Area, Hubei

Through the study on the material recently collected from the Lower Cambrian Shuijingtuo Formation in Yichang and Changyang of the eastern Yangtze Gorge area, Hubei, morphology and ontogeny of various stages of specimens of eodiscoid trilobite Tsunyidiscus acutus were described and discussed, which include supplementary description on the protaspides of T. acutus. And according to the size and morphological characteristics the adult specimens were subdivided into 3 stages: early stage, middle stage and late stage and the morphological changes of each stages through ontogeny were also described and discussed, such as the shape of glabella and frontal glabellar lobe, the fusion of fixigenal area in frontal of the glabella and the lengthening (sag.) of anterior border. The most prominent one is the first discovery of two complete meraspid period specimens of T. acutus (degree 0 and degree 1), which provide significant information on the ontogenetic features of meraspid period of T. acutus, and also have special reference to the study on the ontogeny of other eodiscoid trilobite.In addition, the firstly discovered protaspides of Sinodiscus changyangensis were described and subdivided into 3 stages (stage 1, stage 2 and stage 3) according to the number axial segments of protopygidium. The main morphological changes of different stages through ontogeny include the migration of terminal part of eye lobes, the appearance of shallow furrow behind the protocranidium and the increase of the number of axial segments and the lengthening (sag.) of protopygidium.