Melanosclerites: A Special Kind of Paleozoic Microfossil and New Discoveries in China
1 Key Laboratory of Metallogenic Prediction of Nonferrous Metals and Geological Environment Monitoring, Ministry of Education, School of Geosciences and Info-Physics, Central-South University, Changsha 410083, China; wwhever@126.com;
2 State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, China.
The term ‘melanosclerite' was first introduced by Eisenack (1942) to describe a type of problematic rod-shaped organic microfossil. Eisenack (1942) erected the Family Melanoskleritoitidae and included nine genera within it. Later systematic studies conducted by Eisenack (1950, 1963), Górka (1971), Taugourdeau (1979), Schallreuter (1981), and Cashman (1992) greatly enlarged the group: a total of 18 genera and 38 species have been included. To date, melanosclerites have been recorded from marine sediments and erratic boulders from lower Cambrian to Upper Devonian strata (Cashman, 1992; Winchester-Seeto & McIlroy, 2006). Melanosclerites have a worldwide distribution. They have been reported previously from Laurentia, Baltica, Gondwana and South China (Cashman, 1992; Winchester-Seeto &Mcllroy, 2006; Sinha & Trampisch, 2013; Tang et al., 2015; see Sinha & Trampisch (2013) for more details of occurrences). However, the biological affinity of melanosclerites is still not fully understood. They have been suggested to have affinities with cnidarians (Eisenack, 1942; Pichler, 1971), thecamoebae (Dunn, 1959) or algae (Górka, 1971). Impressively, the hypothesis of Cashman (1992) that melanosclerites have a close relationship with cnidarians has been widely accepted.
Melanosclerites are variable in overall shapes (Fig. 1). They are mainly divided into two types: the ‘skeleton' and ‘pleuridien' (Fig. 1A; Eisenack, 1942; Trampisch, 2007). Pleuridien have been divided into three forms: stalked pleuridien, unstalked pleuridien and undifferentiated pleuridien, as suggested by Górka (1971). Other forms such as dumb-bell pleuridien (Fig. 1B) and elongate pleuridien (Fig. 1C, D, E) are also common melanosclerites.
The first Chinese record of melanosclerites was reported by Tang et al. (2015). Melanosclerites were collected across the Llandovery-Wenlock boundary in the Ziyang-Langao region, Shaanxi, NW China. All of the species they found are pleuridien and have been assigned to Melanoporella clava Schallreuter,Melanoporella sp.,and an undetermined melanosclerite. In the present study, more new materials, were found in the Tarim Basin, Xinjiang Uygur Autonomous Region; Shangrao, Jiangxi Province; Shiqian, Guizhou Province; and Jiangshan, Zhejiang Province. The findings of the Chinese materials greatly improve the record of this fossil group. More importantly, the discovery of more complete‘skeleton' fossils will be critical in understanding the affinity of melanosclerites.
Figure 1 Illustrations of representative melanosclerites. A. Skeleton (ske) and pleuridien (ple) of melanosclerite; B. Dumb-bell pleuridien Melanosteus acutus anceps Eisenack 1942; C. Elongate pleuridien Melanosteus acutus anceps Eisenack 1942; D, E. Elongate pleuridien Miraehitina? polypes Eisenack 1931.According to Górka(1971),A are undifferentiated pleuridien;B and C are stalked pleuridien; D and E are unstalked pleuridien. Scale bar=100 μm.
Acknowledgements This work was financially supported by the National Natural Science Foundation of China (No, . 41772001, 41402010, 41521061). This study is a contribution to the International Geoscience Programme (IGCP) Project 653.
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