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

摘要: The earliest growth of post-metamorphic (post-larval) shells in two species Eohadrotreta is described from the Cambrian Shuijingtuo Formation South China. Two different patterns can be observed by quantifying developmental variations size and shape successive stages shell (including pedicle foramen forming stage, enclosing stage intertrough increasing stage) zhenbaensis Eohadrotreta? zhujiahensis. never enclosed within metamorphic E. zhenbaensis, while E.? zhujiahensis located directly outside after stage. A strongly allometric pattern E. zhenbaensis demonstrated early enclosure foramen; an accelerated lengthening ventral associated with development a more complex dorsal median septum during By contrast, demonstrates possible paedomorphic delayed decreased This ontogenetic sequence represents marginal accretionary formation foramen, which resembles that linguloid brachiopods. Furthermore, process seems to recapitulate likely evolutionary transition Botsfordiidae, open delthyrium, Acrotheloidea, foramen. study provides unique opportunity obtain complete understanding acrotretoids, casts new light on phylogeny lingulate