Dilleniaceae Leaf Fossils from Late Gondwanan Australia Challenge Biogeographic and Paleoclimatic Assumptions

Premise of research. The pantropical to Australian-temperate Dilleniaceae are often considered Gondwanan in origin, but no fossils of the family have been reported from Gondwana. Previously, the only accepted Dilleniaceae fossils were Eocene seeds from the United Kingdom. Here, we report organically preserved Dilleniaceae leaves from the late middle Eocene of southeastern Australia, which then retained its last connections to Antarctica as part of east Gondwana.Methodology. We describe Eocene dilleniaceous leaves from the Anglesea coal mine in Victoria, Australia (paleolatitude ca. 54°S), and we revise their age using palynological analysis of a legacy sediment sample.Pivotal results. We confirm the age of the Anglesea flora as most likely late middle Eocene (Bartonian, ca. 41–38 Ma). The Doliofolium cooksoniae gen. et sp. nov. leaf fossils have distinctive architectural and cuticular traits of Dilleniaceae, and their leaf architecture closely resembles Doliocarpus. Thus, the fossils suggest a previously unknown, ancient Gondwanan radiation and Australian extinction of the extant Neotropical subfamily Doliocarpoideae, and they show no close relationship with living Australian or Asian Dilleniaceae. Variation in leaf architecture among the 31 specimens of the new species would suggest at least five morphotypes if cuticular data were not considered, documenting a normally cryptic error source affecting among-species averages of leaf physiognomy variables that are widely used to estimate paleoclimates.Conclusions. Doliofolium cooksoniae provides the first new fossil record of Dilleniaceae in almost a century and the first Gondwanan occurrence. By the Eocene, Dilleniaceae had a wide distribution that included but did not necessarily originate from Gondwana. Present-day distributions often provide misleading information about a clade’s early history, as seen here. Our findings demonstrate the risks of conjecturing Gondwanan or other paleogeographic “origins” without adequate paleontological and geological evidence.