Are the liverworts really that old? Cretaceous origins and C enozoic diversifications in L epidoziaceae reflect a recurrent theme in liverwort evolution

Estimating the temporal origins of lineage diversity adds an important dimension to understanding diversity generating processes. In lineages with a sparse fossil record, molecular phylogenetic methods provide a means for estimating divergence times. In the present study, we use publicly available sequence data from the chloroplast genome of liverworts to simultaneously estimate significant divergence dates across all classes and orders of liverworts ( M archantiophyta). We show that, although there is great potential in synthetic dating analyses of sequence data, missing sequences can reduce the reliability of estimates, and that calibration priors should be interpreted with caution. Using the liverwort dataset as a broad outgroup, we obtain the first divergence time estimates for a large family of leafy liverworts; the L epidoziaceae ( J ungermanniidae). The L epidoziaceae originated in the early C retaceous with subsequent establishment of main lineages in the late C retaceous. Divergence time estimates are consistent with C enozoic diversification in L epidozia , T elaranea , and B azzania . Evidence was found for similar patterns of ancient origins followed by C enozoic diversification in R icciaceae ( M archantiopsida), P elliaceae and F ossombroniaceae ( P elliidae), and M etzgeriaceae ( M etzgeriidae), and adds to reports of similar patterns in L ejeuneaceae ( J ungermanniidae, P orellales), and P lagiochilaceae ( J ungermaniidae, J ungermanniales). The liverworts might be the living relatives of one of the earliest groups of land plants, but much of the extant diversity has evolved in the C enozoic. © 2012 T he L innean S ociety of L ondon, B iological J ournal of the L innean S ociety , 2012, ••, ••–••.