Ancestral echinoderms from the Chengjiang deposits of China

摘要

Deuterostomes are a remarkably diverse super-phylum, including not only the chordates (to which we belong) but groups as disparate as the echinoderms and the hemichordates. The phytogeny of deuterostomes is now achieving some degree of stability, especially on account of new molecular data, but this leaves as conjectural the appearance of extinct intermediate forms that would throw light on the sequence of evolutionary events leading to the extant groups. Such data can be supplied from the fossil record, notably those deposits with exceptional soft-part preservation. Excavations near Kunming in southwestern China have revealed a variety of remarkable early deuterostomes, including the vetulicolians and yunnanozoans. Here we describe a new group, the vetulocystids. They appear to have similarities not only to the vetulicolians but also to the homalozoans, a bizarre group of primitive echinoderms whose phylogenetic position has been highly controversial.