ABSTRACT
The early evolution of the deuterostomes, and the echinoderms, is still largely problematic. Molecular biology has provided a series of exceptional insights, but can do little to explain either the remarkably diverse bodyplans of the component phyla or their original appearance. Recent work on fossils from the famous soft-bodied fossil localities in Yunnan (Chengjiang Lagerstätte: Lower Cambrian) suggests that the vetulicolians, originally described as arthropods, may have a crucial position in the early evolution of the deuterostomes, and by implication the echinoderms. The strikingly bipartite body and evidence for anterior gill slits suggests a possible, if controversial, connection to the “calcichordates”. Key evolutionary steps are yet to be discovered, but in conjunction with the related yunnanozoans (also from Chengjiang) we argue that the fossil record may provide unique historical insights into the origins of not only the echinoderms, but also the other major groups of deuterostomes. Whilst our hypotheses still need extensive discussion we are confident that if the key to deuterostome evolution lies anywhere it is in the Chengjiang fossil localities.
