Soft-Bodied Gelatinous Fossils (Cnidaria/Ctenophora) from the Lower Cambrian, Chengjiang Biota, Yunnan Province, China  

The Early Cambrian Chengjiang biota of southwestern China has yielded exquisite examples of soft-bodied preservation.  Previously reported among these were jellyfish, sea anemones, and ctenophores.  These fossils provide unparalleled insights into the early evolution of these groups at an important point in the Cambrian explosion of metazoan life.  Here, we report new fossils from the celebrated Chengjiang biota, interpreted as extremely fragile gelatinous taxa belonging to Ctenophora, as well as possible siphonophores and hydroids. 

The significance of ctenophores has been highlighted in recent molecular studies which place them as a sister group to all metazoans.  The presence in the new fossils of eight sets of delicate comb rows, comb plates, a gut, and possible tentacular sheaths; and other features of the anatomy; are all remarkably consistent with some modern ctenophores.  However, we apply caution to interpretations of some other fossils (from the Chengjiang biota and the Burgess Shale) with reputed comb rows as they may represent unrelated features. 

We report possible hydroids and a siphonophore for the first time.  The hydroids are fragmental, and preserved as rows of polyps on individual branches.  A single specimen of a jellyfish-like siphonophore possesses elongate tentacles and possible gonozooids. 

Details revealed by these remarkable fossils indicate close phylogenetic connections between the 515-million-year-old Chengjiang cnidarians and ctenophores, and their living relatives.  These fossils are of great significance to the phylogenies of their respective groups and suggest possible ancestors much deeper in Neoproterozoic time.