Extinction and opportunistic evolution among late Wenlock graptolites



The late Homerian was a time of profound importance to graptolites. Following the complete extinction of Cyrtograptus and the near extinction ofMonograptus(s.s.)at the end of thelundgrenitestis Zone(lower Homerian, upper Wenlock), the morphologically simple and long-ranging Pristiograptus dubius lineage 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’ praedeubeli group, gave rise to similar but more complex species, such as ‘P.‘ ludensis and ‘P.‘deubeli, which in turn gave rise to Ludlow taxa, including Saetograptus (s.l.) and Pseudomonclimacis. The other clade, the Lobograptusgroup, gave rise to Ludlow taxa Lobograptus, Neolobograptus, Bohemograptus, and Neocucullograptus some with very complex thecal structures. Ludlow and younger monograptid faunas therefore comprise at least three separate lineages: Monograptus (s.s.), the Lobograptus group (clade), and the ‘Pristiograptus’ praedeubeli group (clade).Cladogenesis, evolution, extinction, Homerian, PRISTIOGRAPTUS, LOBOGRAPTUS