Lower Aeronian (Llandovery, Silurian) graptolites of the generaRastritesandStavrites: systematics, biostratigraphy and palaeobiogeography

Abstract

AbstractThe lower Aeronian graptolite speciesRastrites longispinus longispinusPerner,R. approximatusPerner,R. peregrinusBarrande,R.? norilskensisObut & Sobolevskaya, andStavrites rossicusObut & Sobolevskaya have been revised using material from China, the Czech Republic, Siberia, Canada and Spain, together with published data.Rastrites longispinus chenxuisubsp. nov. is recognized as a new biogeographical subspecies known only from China and Canada.Rastrites guizhouensisMuet al.,R. confertusChen & Lin andStavrites laticellatusObut & Sobolevskaya, are all considered to be junior synonyms ofS. rossicus.Rastrites geinitziiTörnquist is regarded as a junior synonym ofR. longispinus longispinus; andR. orbitusChurkin & Carter andR. hemigyratusChen & Lin are considered to be junior synonyms ofR.? norilskensis. We propose that a distinctR.? norilskensisBiozone can be recognized between a lowest AeronianDemirastrites triangulatusorD. triangulatus – D. pectinatusBiozone in Siberia and northern Canada (possibly in South China, with future work) and the overlyingLituigraptus convolutusBiozone. Cluster analysis of the palaeogeographical distribution of species ofRastritesandStavritessupports 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.