Extinction and opportunistic evolution among late Wenlock graptolites

摘要

The late Homerian was a time of profound importance to graptolites. Following the complete extinction ofCyrtograptusand the near extinction ofMonograptus(s.s.)at the end of thelundgrenitestisZone(lower Homerian, upper Wenlock), the morphologically simple and long‐rangingPristiograptus dubiuslineage underwent rapid (opportunistic) cladogenesis during the succeeding upper Homerian. Two clades, each with novel and sometimes complex sicular and thecal structures, appeared. One clade, the‘Pristiograptus’ praedeubeligroup, gave rise to similar but more complex species, such as ‘P.‘ ludensisand ‘P.‘deubeli, which in turn gave rise to Ludlow taxa, includingSaetograptus(s.l.) andPseudomonclimacis.The other clade, theLobograptusgroup, gave rise to Ludlow taxaLobograptus, Neolobograptus, Bohemograptus, andNeocucullograptussome with very complex thecal structures. Ludlow and younger monograptid faunas therefore comprise at least three separate lineages:Monograptus(s.s.), theLobograptusgroup (clade), and the‘Pristiograptus’ praedeubeligroup (clade).Cladogenesis, evolution, extinction, Homerian, PRISTIOGR