Cyrtograptids from the Telychian (upper Llandovery) of Kinnekulle Mountain, Southern

Postprint This is the accepted version of a paper published in GFF. This paper has been peer-reviewed but does not include the final publisher proof-corrections or journal pagination. Access to the published version may require subscription. 1 The late Llandovery graptolite fauna of the Retiolites Shales on Kinnekulle Mountain in the province of Västergötland has long been known but never illustrated or studied in detail. New collections of graptolites from an interval at the very top of the exposed succession confirm previous reports of cyrtograptids, which make the shales on Kinnekulle the youngest preserved Palaeozoic rocks in the area. The co-occurrence of Oktavites spiralis and Cyrtograptus lapworthi constrain the strata to the lower lapworthi Biozone of the upper Telychian. The associated graptolite fauna comprises numerous monograptids and Retiolites geinitzianus as well as a new species of Cyrtograptus. The new species, C. kinnekullensis n. sp., is characterised by its open coiling and the presence of a second order cladium on the second thecal cladium. This early occurrence of a cyrtograptid species with a second order cladium on Baltica matches evolutionary patterns observed in Laurentia, suggesting that the ability to grow cladia of both first and higher order evolved approximately synchronously and at the very beginning of cyrtograptid evolution. Analysis on the positions of cladia in C. lapworthi indicates that the most proximal cladium was not necessarily the first to be formed. It appears that the first cladium originated distally and more proximal cladia formed afterwards as a counterbalance to the growing rhabdosome, allowing the organism to remain stable in the water column.