Carsten Gröhn

A Comprehensive Assessment of the Fossil Record of Liverworts in Amber

Abstract Amber, a fossilized angiosperm or conifer tree resin, is a valuable source of new information on the diversity of liverworts in the Late Cretaceous and Cenozoic. This chapter reviews the fossil record of liverworts in amber, and discusses several problems with regard to the classification of incompletely preserved specimens of these plants. Putative epiphytic species assignable to the order Porellales are disproportionally well represented; other species probably grew on the trunk bases of the resiniferous trees or in their close proximity. Divergence time estimates based on a comprehensive cp DNA dataset of extant liverworts and a root calibration derived from earlier studies yield age intervals that are in good accordance with current taxonomic hypotheses on amber fossils, and provide evidence of a general congruence of both data sources. Lineage-through-time plots indicate the occurrence of increased diversification of the largely epiphytic Porellales since the Cretaceous and a constant accumulation of diversity in the predominantly generalistic sister clade Jungermanniales. These findings underline the prime importance of amber fossils to understand accurately crown group evolution in epiphytic liverwort lineages, and call for the expansion of efforts to find additional fossils of these plants in Cretaceous amber deposits.