贵州剑河中寒武世中期甲劳组水母状化石的发现

MEDUSIFORM FOSSILS FROM THE MIDDLE MIDDLE CAMBRIAN JIALAO FORMATION OF JIANHE COUNTY, GUIZHOU, CHINA

贵州剑河革东镇八郎村南甲劳组中部钙质白云岩中新近发现的具有粗强放射状辐管的水母状化石和其下凯里组中具细辐管及同心环的拟轮盘水母(Pararotadiscus)有明显区别,属于伊尔东钵科(Eldoniidae)。其层位晚于中寒武世早期凯里生物群中拟轮盘水母(Pararotadiscus)层位1个化石带,属中寒武世中期,是该类化石在中国的最高层位,相当于北美布尔吉斯页岩生物群中Eldonia化石层位。

Medusiform eldoniids, which are a group of pelagic animals with coiled alimentary canal and tentacles, are confined to the Cambrian, especially in lower to middle Cambrian of Poland, Spain, Siberia, North America and South China, etc. Eldoniids are one of important components of the three Burgess Shale-type hiotas, including the Chengjiang Biota, Kaili Biota and Burgess Shale Biota. Here we describe a medusiform fossil from the middle Cambrian Jialao Formation at Balang village, Gedong Town, Jianhe County, Guizhou Province. Although the fossil has the similar features as eldoniids with bifurcated lobes, the poor preservation of a single specimen makes it premature to assign it to a genus or species. The undefined genus and species is discoid in shape with 32-36 rough radial lobes. The fossil horizon is about 1 fossil zone above that of Pararotadiscus guizhouensis from the Kaili Biota. Based on the study of trilobites, the geological age is middle middle Cambrian. It is the highest horizon of eldoniids in China. In the past, the exceptional preservation of soft-bodied fossils was often discovered in the mudstone, and was infrequent in the carbonate. Thus this occurrence in the Jialao Formation is an important evidence of soft-bodied fossils in the carbonate. The medusiform fossil reported here provides new information of the Cambrian life.