The first fossil Dinckleria (Plagiochilaceae: Marchantiophyta) from Eocene-age Anglesea amber of Australia

Dinckleria opaca M.A.M.Renner & M.Paulsen is described from Anglesea amber for fossils previously reported in the literature as an undetermined liverwort of the family Plagiochilaceae. The fossils are fragmentary and critical character systems are not preserved, complicating generic attribution. Membership in Dinckleria is supported by the ovate–elliptic and nearly symmetrical leaf shape, the trilobed leaf apex, and the vestigial, unlobed, triangular underleaves. Fossil preservation is poor, with no evident impregnation of plant material by resins, such that the fossil comprises the amber–air interface capturing the volume of the included plant material, that in turn contains highly degraded and disaggregated remnants of the plant itself. The amber–air interface has trace impressions of internal cell walls standing proud above the collapsed and concave external walls, typical of dehydrated plant material, and appears to have experienced minor deformation and distortion during amber formation, such that these leaf cell impressions and leaf cell surfaces are incompletely preserved. The age of the fossil, at 42 Ma, contrasts with the shallow phylogenetic divergences within D. pleurata, the species currently extant in Victoria and also south-east Queensland and New Zealand, suggesting a complex biogeographic history for the Dinckleria lineage in south-east Australia involving extinction and recolonisation by long-distance dispersal.