Leaf fossils show a 40-million-year history for the Australian tropical rainforest genus Megahertzia (Proteaceae)

Abstract

ABSTRACT Well-preserved leaf fossils from the Middle Eocene Anglesea site in Victoria are assigned to a new species of Megahertzia (M. paleoamplexicaulis R.J.Carp. & Rozefelds), a genus of Proteaceae now represented by a single species, M. amplexicaulis A.S.George & B.Hyland, in the Wet Tropics rainforests of Queensland. Megahertzia-like cuticular remains also occur in the Eocene Mount Hotham assemblage of Victoria, and pollen closely conforming to Megahertzia (i.e. Proteacidites latrobensis W.K.Harris) occurs widely in Cenozoic sediments of Australia and in New Zealand. All these records add to other fossil evidence that many species of Australian rainforest Proteaceae are the last vestiges of formerly much more widespread lineages. The fossil leaves are near-identical in architecture and cuticular features to lobed leaves of M. amplexicaulis, including that they have small teeth, stomata in well-defined areoles, and fine cuticular striations. Moreover, where preserved, the leaf fossils show amplexicaul bases, a unique (apomorphic) trait of the extant species. The apparent absence at Anglesea of simple (unlobed) leaves in Megahertzia and two other taxa of fossil Proteaceae is discussed; this leaf type could have evolved convergently in response to forest canopy heat increase as Australia drifted towards the Equator.