Rogercooperia, a new genus of Ordovician glossograptid graptolite from southern Scotland and New South Wales, Australia

Abstract

Synopsis Rogercooperia phylloides (Elles & Wood 1908) gen. nov. and R. paucispinosus (Sherwin & Rickards) form the basis of a new genus evolutionarily related to the last of the glossograptids in the wilsoni Biozone (early Caradoc) of Scotland, UK and the calcaratus Biozone (highest Gisbornian) of New South Wales, Australia. The similar genus Nanograptus Hadding (1915), from the early Caradoc of Scandinavia, is reviewed, and is considered a late evolutionary derivative of Cryptograptus Lapworth (1880). Rogercooperia and Nanograptus are convergent genera. Although of different evolutionary lineages both show loss of proximal spinosity, loss of rhabdosomal spinosity, and lessening of thecal spinosity, resulting in an overall similar appearance. The loss of spinosity is typical of many lineages of biserial graptolites in the late Caradoc and Ashgill. The early development of the colonies, in both genera, includes a low metasicular origin of thl 1 , again a late evolutionary feature.