Early Cambrian radiation of brachiopods: A perspective from South China

Abstract

Brachiopods, a group of benthic suspension-feeding marine invertebrates, made their first appearance in the Lower Cambrian. In the Yangtze Platform (South China), well-exposed Lower Cambrian stratigraphic succession represents shallow to deeper water environments. Strata from eastern Yunnan, southern Shaanxi and the Yangtze gorges areas of western Hubei Province, deposited in muddy-siltstone and carbonate lithofacies, contained an abundant variety of brachiopods, including all the representatives of the subphylum Linguliformea and the calcareous-shelled genera of Kutorgina and Nisusia from the subphylum Rhynchonelliformea. Thus the fossil assemblage bears witness to the first major phase of evolutionary radiation of brachiopods during the ‘Cambrian explosion’ interval of metazoans. Brachiopods from the celebrated Chengjiang fauna have exquisitely preserved soft-tissues, which reveal the body plans and evolutionary acquisition of morphological novelties of the early stocks, and also provide a good opportunity for testing the analogies with the stem groups from the extant representatives. These fossils have corroborated the view that brachiopods developed complex organization of tissues, and achieved considerable evolutionary success already by the onset of ‘Cambrian Explosion’. Thus it is not improbable that a large part of this radiation occurred within, or only just before early Cambrian time. Studies of Chengjiang brachiopods suggest that attachment by a pedicle to the substrate was probably the most common relationship of Cambrian brachiopods with the substrate where they inhabited.