Plant macrofossil evidence for the environment associated with the Riversleigh fauna

Abstract

Fossil plant organs from probable Oligocene nodules at the Dunsinane Site at Riversleigh, Queensland, were studied. The deposit consists of a low diversity assemblage of reproductive and vegetative organs dominated by a single taxon of Casuarinaceae. The species of Casuarinaceae has affinities with Casuarina and Allocasuarina in having more four teeth per whorl on the photosynthetic branchlets and stomata hidden in deep furrows filled with trichomes, and as such represents the earliest known record of sub-family Cryptostomae. The species is described as Cryptostomiforma quinata gen. et sp. nov. A leaf species is assigned to Alectryon (Sapindaceae) on the basis of the anatomy of abaxial cuticular features. In particular, the morphology is indistinguishable from extant A. affinis, a species currently endemic to New Guinea. Organs with possible affinities to Rubus or Capparis were examined. The assemblage is interpreted as a possible vegetation mosaic, containing both deciduous vine thickets and sclerophyllous habitats. No evidence for the presence of rainforest was found and the fossils are not consistent with extensive lowland tropical rainforest.