A Burmese amber fossil of &amp;lt;i&amp;gt;Radula&amp;lt;/i&amp;gt; (Porellales, Jungermanniopsida) provides insights into the Cretaceous evolution of epiphytic lineages of leafy liverworts

Julia Bechteler,Kathrin Feldberg,Oscar Alejandro Pérez-Escobar,Alexander R. Schmidt,Matthew A. M. Renner,Bo Wang,Jochen Heinrichs,Alfons Schäfer-Verwimp

doi:10.5194/fr-20-201-2017

Abstract

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.

Highlights

DNA-based divergence time estimates suggest major changes in the composition of epiphyte lineages of liverworts, mosses, and ferns during the Cretaceous radiation of main angiosperm lineages (Schuettpelz and Pryer, 2006; Newton et al, 2007; Hennequin et al, 2008; Cooper et al, 2012; Feldberg et al, 2014)
The same pattern was observed for the number of female bract pairs, which changed from one to two female bract pairs within subgenus Odontoradula
The lack of gemmae production was inferred as the ancestral state for Radula and a transition to the development of gemmae occurred independently within the subgenera Odontoradula, Volutoradula Devos, M

Summary

Introduction

DNA-based divergence time estimates suggest major changes in the composition of epiphyte lineages of liverworts, mosses, and ferns during the Cretaceous radiation of main angiosperm lineages (Schuettpelz and Pryer, 2006; Newton et al, 2007; Hennequin et al, 2008; Cooper et al, 2012; Feldberg et al, 2014) These lineages may have benefitted from the more humid climate of angiosperm-dominated forests compared to gymnosperm forests (Boyce et al, 2010; Boyce et al, 2010; Boyce and Leslie, 2012; Zwieniecki and Boyce, 2014); evidence from the fossil record is scarce (Taylor et al, 2009).

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