Trunk segmentation of Cambrian eodiscoid trilobites.
Here we report, from Cambrian Series 2 of Chongqing, southern China, on some three-dimensionally phosphatized exoskeletons representing a series of instars of a specialized eodiscoid trilobite Badiscus spinosus gen. et sp. nov. The preservation is unusual and its protaspides (the youngest juveniles) belonging to different growth stages markedly exhibit some "embryonic trunk segments," which imply the specification of all body segments during embryogenesis. This previously unknown style of tagmosis, as being inconsistent with the conventional view of sequential segmentation during postembryonic anamorphosis, emphasizes the complexity of trilobite trunk segmentation during ontogeny and indicates for the first time that epimorphic development, like other known patterns during postembryonic development, may have already been adopted by some of the earliest trilobites.
Zhang
Xi-guang
XG
Key Laboratory for Palaeobiology, Yunnan University, Kunming 650091, China. xiguang.zhang@hotmail.com
Clarkson
Euan N K
EN
D000818:Animals; D002681:China; D005580:Fossils