A Cycas L. (Cycadaceae) Leaf from the Miocene of Northern South Australia

Premise of research. Cycads in the extant Australian flora span both Cycadaceae and Zamiaceae, with Cycas-the sole genus in Cycadaceae-considered to have dispersed into Australia from East Asia and speciated there since the Miocene. This premise is untested because of the lack of a fossil record for Cycas in Australia. Methodology. We describe a pinnate partial cycad leaf impression from a Miocene fossil site in northern South Australia. Diagnostic characters for potential matches with other taxa, such as pinnate ferns, pinnate palms, and the univeined Podocarpus, were assessed against the fossil and eliminated. Multivariate analyses of morphological data from extant Australian Cycas species and likely morphological matches from Asia are used to interpret the fossil's possible affinities. Pivotal results. The fossil is a pinnate leaf with opposite linear to lanceolate leaflets with a single prominent midvein and no secondary veins, diagnostic of Cycas, and the lamina has few (ca. 20) widely spaced, long, broad leaflets. Apparent parallel veins on two leaflets are interpreted as preservation artifacts. This leaf morphology is more consistent with extant Cycas species of the former section Stangerioides from Southeast Asia than with extant Australian taxa from section Cycas, which are characterized by many (100-410) moderately to closely spaced leaflets with narrow laminae. This fossil is a significant temporal and geographic range extension for Cycas and the first record of a fossil Cycas from Australia. Co-occurring angiosperm taxa from the fossil flora are consistent with this cycad being part of a landscape dominated by sclerophyllous forest or woodland under a wet, though seasonally dry, possibly monsoonal climate. Conclusions. Cycas was present in Australia by the Miocene, although potentially representing a lineage absent from modern Australia, likely under a monsoonal climate consistent with that of extant species of Australian Cycas and Southeast Asian section Stangerioides.