Post-metamorphic allometry in the earliest acrotretoid brachiopods from the lower Cambrian (Series 2) of South China, and its implications

The earliest growth of post-metamorphic (post-larval) shells in two species of Eohadrotreta is described from the Cambrian Shuijingtuo Formation of South China. Two different growth patterns can be observed by quantifying developmental variations in size and shape of successive stages of post-metamorphic shell growth (including the pedicle foramen forming stage, pedicle foramen enclosing stage and intertrough increasing stage) of Eohadrotreta zhenbaensis and Eohadrotreta? zhujiahensis. The pedicle foramen is never enclosed within the metamorphic shell of E. zhenbaensis, while the enclosed pedicle foramen of E.? zhujiahensis is located directly outside the metamorphic shell after the pedicle foramen enclosing stage. A strongly allometric growth pattern of E. zhenbaensis is demonstrated by the early enclosure of the pedicle foramen; an accelerated lengthening of the ventral intertrough is associated with the development of a more complex dorsal median septum during the intertrough increas...

基于中国南方寒武纪水井沱组的化石材料，本文描述了两种始小哈德罗贝属（Eohadrotreta）物种的变态后（幼虫后）壳体早期生长过程。通过量化镇巴始小哈德罗贝（Eohadrotreta zhenbaensis）和疑似朱家河始小哈德罗贝（Eohadrotreta? zhujiahensis）变态后壳体生长各连续阶段（包括肉茎孔形成期、肉茎孔封闭期及间槽增多期）的尺寸与形态发育变异，可观察到两种不同的生长模式。镇巴始小哈德罗贝的肉茎孔从未被封闭于变态壳内；而疑似朱家河始小哈德罗贝的肉茎孔在封闭期后，其封闭的肉茎孔直接位于变态壳外侧。镇巴始小哈德罗贝表现出强烈的异速生长模式，这可由其肉茎孔的早期封闭得以证明；在间槽增多期，腹侧间槽的加速延长与更复杂的背中隔发育相关联……