Enigmatic discoidal macrofossils with central ring from the Ediacaran Jiangchuan biota, Southwest China

Abstract

The Jiangchuan biota is a diverse macrofossil assemblage from the Jiucheng Member of the Dengying Formation, in the uppermost Ediacaran (Sinian) of Eastern Yunnan, Southwest China. This biota is well known for its macroalgal fossils preserved as carbonaceous compressions, but co‐occurring taxa have remained poorly documented. Here, we present new discoidal macrofossils from the Jiangchuan biota, which we interpret as eumetazoan‐grade organisms of uncertain affinities. These disc‐like fossils are preserved as smooth, well‐defined carbonaceous impressions with a tube‐like peripheral zone. Most have a thick, three‐dimensional carbonaceous ring centrally, which we interpret as a possible remnant of the perioral musculature and innervation. The morphology of these problematica invites comparison with other putative Neoproterozoic medusoids from the Nanfen and Xingmincun Formations of the Jilin and Liaoning areas, Northeast China, and with the enigmatic spiral‐like fossil Eoandromeda octobrachiata of the Doushantuoian Wenghui biota in Guizhou. Based on the shared presence of central, dorsally oriented ring‐like structures in these fossils, we speculate that a perioral annular nervous system may have been widespread among Ediacaran discoidal organisms, and that it might represent a plesiomorphic feature for Eumetazoa.