Phylogenetic relationships among Adelograptus, Ancoragraptus and Psigraptus

摘要

New graptolite material from the Mungok Formation, Yeongwol, Korea, suggests that psigraptids evolved from a species of Ancoragraptus. The main trait of the proposed lineage is a reclined rhabdosome, stipe reduction, and metathecal separation. Ancoragraptus psigraptoides new species, which is the intermediary between Adelograptus sp. 1 and Psigraptus jacksoni, is described. The free metasicula and slightly reclined stipes appear first in Ancoragraptus psigraptoides. A possible route for the lineage is discussed: Adelograptus sp. 1–Ancoragraptus psigraptoides–Psigraptus jacksoni.