A Burmese amber fossil of Radula (Porellales, Jungermanniopsida) provides insights into the Cretaceous evolution of epiphytic lineages of leafy liverworts
- 1Department of Biology and GeoBio-Center, Ludwig Maximilian University, Menzinger Straße 67, 80638 Munich, Germany
- 2Department of Geobiology, Georg August University, Goldschmidtstraße 3, 37077 Göttingen, Germany
- 3Royal Botanic Gardens and Domain Trust, Mrs Macquaries Road, Sydney, NSW 2000, Australia
- 4State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, No.39, East Beijing Road, Nanjing 210008, China
- 5Department of Identification and Naming, Royal Botanic Gardens Kew, Richmond, TW9 3AB, UK
- 6Mittlere Letten 11, 88634 Herdwangen-Schönach, Germany
Abstract. DNA-based divergence time estimates suggested major changes in the composition of epiphyte lineages of liverworts during the Cretaceous; however, evidence from the fossil record is scarce. We present the first Cretaceous fossil of the predominantly epiphytic leafy liverwort genus Radula in ca. 100 Myr old Burmese amber. The fossil's exquisite preservation allows first insights into the morphology of early crown group representatives of Radula occurring in gymnosperm-dominated forests. Ancestral character state reconstruction aligns the fossil with the crown group of Radula subg. Odontoradula; however, corresponding divergence time estimates using the software BEAST lead to unrealistically old age estimates. Alternatively, assignment of the fossil to the stem of subg. Odontoradula results in a stem age estimate of Radula of 227.8 Ma (95 % highest posterior density (HPD): 165.7–306.7) and a crown group estimate of 176.3 Ma (135.1–227.4), in agreement with analyses employing standard substitution rates (stem age 235.6 Ma (142.9–368.5), crown group age 183.8 Ma (109.9–289.1)). The fossil likely belongs to the stem lineage of Radula subg. Odontoradula. The fossil's modern morphology suggests that switches from gymnosperm to angiosperm phorophytes occurred without changes in plant body plans in epiphytic liverworts. The fossil provides evidence for striking morphological homoplasy in time. Even conservative node assignments of the fossil support older rather than younger age estimates of the Radula crown group, involving origins for most extant subgenera by the end of the Cretaceous and diversification of their crown groups in the Cenozoic.