Lower Aeronian (Llandovery, Silurian) graptolites of the genera Rastrites and Stavrites: systematics, biostratigraphy and palaeobiogeography

Abstract

AbstractThe lower Aeronian graptolite species Rastrites longispinus longispinus Perner, R. approximatus Perner, R. peregrinus Barrande, R.? norilskensis Obut & Sobolevskaya, and Stavrites rossicus Obut & Sobolevskaya have been revised using material from China, the Czech Republic, Siberia, Canada and Spain, together with published data. Rastrites longispinus chenxui subsp. nov. is recognized as a new biogeographical subspecies known only from China and Canada. Rastrites guizhouensis Mu et al., R. confertus Chen & Lin and Stavrites laticellatus Obut & Sobolevskaya, are all considered to be junior synonyms of S. rossicus. Rastrites geinitzii Törnquist is regarded as a junior synonym of R. longispinus longispinus; and R. orbitus Churkin & Carter and R. hemigyratus Chen & Lin are considered to be junior synonyms of R.? norilskensis. We propose that a distinct R.? norilskensis Biozone can be recognized between a lowest Aeronian Demirastrites triangulatus or D. triangulatus – D. pectinatus Biozone in Siberia and northern Canada (possibly in South China, with future work) and the overlying Lituigraptus convolutus Biozone. Cluster analysis of the palaeogeographical distribution of species of Rastrites and Stavrites supports the hypothesis that two graptolite palaeobiographical provinces can be defined in the early Aeronian: a low‐latitude Circumequatorial Province including northern Laurentia, South China, Siberia and peri‐Siberian terranes; and a largely mid‐latitude Rheic – West Gondwana Province comprising Avalonian Britain, the Baltic area, central Europe, western and southern Europe, and cratonic North Africa. None of our studied taxa exhibits a cosmopolitan distribution. Our systematic revision has a significant impact on our palaeogeographical interpretations.