First Miocene record of Akaniaceae in Patagonia (Argentina): a fossil wood from the early Miocene Santa Cruz formation and its palaeobiogeographical implications

Today, Akaniaceae are confined to south-eastern Queensland and north-eastern New South Wales (Australia), south-eastern China and northern Vietnam. Akanioxylon santacrucensis gen. and sp. nov. is described as the first fossil wood of Akaniaceae from the early Miocene Santa Cruz Formation (c. 18-16 Ma; Burdigalian) on the Atlantic coast of Santa Cruz Province, Argentina. The diagnostic features are growth rings inconspicuous, with most latewood vessels only slightly narrower than earlywood vessels; diffuse porous wood; mainly solitary vessels, occasionally radial or tangential multiples and clusters; mainly simple, occasionally reticulate and rarely scalariform with many interconnections between bars perforation plates; bordered, minute to small intervessel pits; axial parenchyma scanty paratracheal and apotracheal diffuse; vessel-ray parenchyma pits with much reduced borders to apparently simple; vessel-axial parenchyma pits scalariform or transitional; mainly multiseriate (four to six cells wide) and rare uniseriate rays, heterocellular, occasionally crystals in ray cells; septate and non-septate fibres with simple to minutely bordered pits. These features resemble the extant Akania and Bretschneidera. The eco-anatomical analysis suggests that this fossil wood grew under temperate to warm-temperate and semi-arid climatic conditions. This record of Akania/Bretschneidera-like wood in South America reinforces the existence of an old relationship with the Australasia flora. The discovery of Akaniaceae in the Santa Cruz Formation extends the record of the taxon in South America c. 30 Ma and 10A degrees S in latitude and suggests that the family was widespread in Patagonia as a component of forests developed in a frost-free humid biome in South American at mid to high latitudes.