Divergence time estimates for several phylogenies of Annelida (Lophotrochozoa)

Annelids are a group of lophotrochozoan worms comprising a large number of species. Historically, the phylogenetic relationship among them has been subject to a lot of research, and in recent times the backbone phylogeny has largely been resolved. The evolutionary histories and trajectories of selected clades within Annelida have been studied, but up until now, molecular dating of all major annelid clades has not been performed yet. Hence, it is the aim of this project to date the divergences between all recognized annelid families, using modern molecular dating techniques and especially concentrating on the origin and basal splitting events in the annelid tree of life. Using both RelTime and Bayesian dating methods on two constrained trees with multiple fossil calibrations, the results revealed a conflict between the sequence data and the putative sipunculan fossil record, in which the former indicated a much younger age for sipunculans than the latter. Under certain fossil calibration schemes, the fossil calibration on Sipuncula caused the age estimates of many basal nodes, especially in MEGA-X, to be pushed back to the mid Ediacaran period or earlier. Considering different possible explanations for the mismatch, the most likely explanation for this is that the putative sipunculan fossil was falsely assigned to sipunculans. Given the results presented herein, annelids evolved about 522-528 Mya, in early/mid Cambrian, which is in agreement with the known fossil record of early annelid fossils