Abstract

Retrophyllum Page is a podocarp genus represented by four extant species of disjunct distribution in tropical South America and Pacific islands. The molecular analysis attests a good correspondence between geography and phylogeny in the genus and the relationships between the four Pacific Islands forms and the South American species. However, recent phylogenetic analysis diverges about the relations between Retrophyllum, Nageia and Afrocarpus and which was their ancestral, yet proposing its common divergence from other Podocarpaceae at near 60 Ma. To Retrophyllum an origin in the Paleogene is proposes, in accord with the scarce fossil record until now known that shows a first appearance in the Eocene-Oligocene boundary of southernmost Argentina and West Australia, followed by those forms from the Early Miocene of New Zealand. Here we report new Retrophyllum-related axes identified in the upper sandstones of Dorotea Formation, where isotopic data indicates ages between 67–69 Ma. The preserved apical shoots exhibit a heterofacially-flattened disposition, bearing pairs of elliptic-oblong leaves, spirally inserted but opposite disposed in two row and in a single plane. Together with the clear midvein in the leaves, such morphology confirms its affinity with modern Retrophyllum representatives, by its unique features between the Podocarpaceae. The new discovery extends the record and the divergence time of the early forms of the genus to the Upper Cretaceous and have important implications in confirm its dispersal strategies and the paleogeography of austral areas at this time interval.