THE FIRST GONDWANAN EUPHORBIACEAE FOSSILS RESET THE BIOGEOGRAPHIC HISTORY OF THE DIVERSE, PALEOTROPICAL MACARANGA-MALLOTUS CLADE

The spurge family Euphorbiaceae is a dominant and diverse element in tropical rainforests worldwide, especially in Asia. The family's limited fossil record restricts the accuracy of biogeographic interpretations, and despite classical ideas of its Gondwanan origins, no reliable spurge macrofossils have come from Gondwana. We report the first Gondwanan macrofossils of Euphorbiaceae, represented by two infructescences from the early Eocene (52 Ma) Laguna del Hunco site in Patagonian Argentina (then part of West Gondwana). The fossils present a highly distinctive character combination of paniculate infructescences bearing short-pedicellate, two-locular, two-seeded, spineless, dehiscent capsular fruits, each fruit with a pair of plumose stigmas. This combination is only seen today in several species of the euphorbiaceous Macaranga-Mallotus clade (MMC), a widespread, well-studied Old-World tropical-understory group often thought to have tropical Asian ancestry. The discovery adds a significant paleotropical component to a growing list of floristic connections from Patagonian paleorainforests through the paleo-Antarctic to modern tropical Asia. Many taxa from Laguna del Hunco associate today with the MMC in the paleotropics, including ecologically significant genera of conifers such as Papuacedrus, Agathis, and Dacrycarpus and the angiosperms Eucalyptus, Castanopsis, and Ceratopetalum. The new fossils are the oldest known for the MMC, physically demonstrating its Gondwanan history. Their discovery makes an Asian origin of the MMC improbable because immense oceanic distances separated Asia and South America at 52 Ma, and, remarkably, no reproductive fossils of the MMC are known from Asia or anywhere in the far-better-sampled Northern Hemisphere. Thus, it is likely that the MMC entered Asia, along with many other Gondwanan survivors, as part of the Neogene Australia-Asia (Sahul-Sunda) collision and biotic exchange.