22 July 2004
Echinoderms: Back to base
An important unsolved question in the phylogeny of the animal kingdom is that of the origin of the echinoderms. Molecular data suggest they are a sister group of the hemichordates, worm-like marine animals with a primitive notochord. But the body plan of modern echinoderms — radially symmetrical invertebrates including sea urchins and starfish — has undergone so much change that it is difficult to imagine what a common ancestor might look like. New finds from China's Chengjiang fossil beds shed light on the matter. The fossils are classified as a new group, the vetulocystids. With gills but lacking later refinements, they sit at the base of the echinoderm line as a sister group between echinoderms and hemichordates.
Ancestral echinoderms from the Chengjiang deposits
of China
D.-G. SHU, S. CONWAY MORRIS, J. HAN, Z.-F. ZHANG &
J.-N. LIU
Nature 430, 422–428 (2002); doi:10.1038/nature02648
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Palaeontology: Echinoderm roots
ANDREW B. SMITH
A bold claim about the origins of the echinoderms is based on newly discovered
fossils from China. But many pieces are still missing from this part of
the fragmented puzzle of life's evolutionary history.
Nature 430, 411–412 (2004); doi:10.1038/430411a
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