EARLIEST CHITINOZOANS DISCOVERED IN THE CAMBRIAN DUYUN FAUNA OF CHINA

Chitinozoans are an enigmatic group of organic-walled marine microfossils with an abundant Lower Ordovician to Upper Devonian fossil record. They achieved maximum species diversity during the Middle Ordovician–Silurian, and their history during the group’s acme is well documented. Nevertheless, information about their origin and early evolution is sparse. Here we report three phosphatized flask-shaped vesicles recovered from the Cambrian Stage 5 (~510 Ma old) Duyun fauna of southern China as the earliest known chitinozoans, Eisenackitina? sp., extending the record of the microfossil group back by at least 20 Myr.

Their exceptional occurrence within an Orsten-type Lagerstätte might imply that the earliest chitinozoan animals may have lived near the sediment flocculent layer with a benthic life style. As small populations with restricted occurrences, the Cambrian chitinozoans left little fossil record until their later colonization of pelagic niches and preservation in organic-rich pelagic mudstones. Our hypothesis of a benthic antecedent for planktonic chitinozoans would be consistent with many other organism groups that have colonized the water column, including ostracods, graptolites and trilobites.