Early postembryonic to mature ontogeny of the oryctocephalid trilobite Duodingia duodingensis from the lower Cambrian (Series 2) of southern China

Many well-preserved, articulated exoskeletons recovered from the early Cambrian (Stage 3) Mingxinsi Formation in Weng'an, Guizhou Province, southern China, permit reconstruction of the early postembryonic to mature (i.e. protaspid to holaspid) ontogeny of the small oryctocephalid trilobite Duodingia duodingensis Chow. It is likely that the type material is a latest stage meraspis, and the species had nine thoracic segments in the holaspid phase rather than the eight suggested previously. The earliest holaspis is relatively small in size (about 3.00 mm in total length), and the succeeding instars show little size-related shape change. Striking changes take place in the morphology of the glabella during early ontogeny including forward extension of the axial furrows until they reach the anterior cephalic margin in meraspid degree 0iii, and narrowing of the glabellar mid-region. This is the first noneodiscid trilobite to show three developmental stages within meraspid degree 0. Documentati...

中国南方贵州省瓮安地区寒武纪早期（第3阶）明心寺组中出土了大量保存完好、关节连接完整的外骨骼标本，为重建小型掘头虫科（Oryctocephalid）三叶虫多定多定虫（Duodingia duodingensis Chow）从胚胎后早期至成熟阶段（即原甲期（protaspid）至全甲期（holaspid））的个体发育（ontogeny）序列提供了可能。该物种的模式标本大概率属于最后期的分甲期（meraspis），且其全甲期阶段的胸节数目应为9节，而非此前研究所提出的8节。最早的全甲期个体体型相对偏小（总长度约3.00毫米），后续各龄期（instar）并未出现与体型变化相关的显著形态改变。在个体发育早期，头鞍（glabella）的形态发生了显著变化：轴沟（axial furrows）向前延伸，直至分甲期0Ⅲ度时抵达头甲前缘（anterior cephalic margin），同时头鞍中部区域出现收窄。这是首个在分甲期0度内展现出三个发育阶段的非新盘三叶虫类（noneodiscid）三叶虫。Documentati...