CONICET | Buscador de Institutos y Recursos Humanos

Southern-Hemisphere terrestrialcommunities from the early Paleocene are poorly known, but abundant Danian plantfossils from the Salamanca Formation in Chubut Province, Argentina areproviding critical data on the diversity and composition of earliest Paleocenefloras. Here, we report the first Danian fossil flowers from South America andpossibly the entire Southern Hemisphere, from a site in the Salamanca Formationdating to ca. 1 million years or less after the end-Cretaceous extinctionevent. The fossil flowers described here, preserved as compressions andimpressions in flat-laminated light gray shale, belong to the family Rhamnaceae(buckthorns). Flowers of Carina grandensis gen. et sp. nov. are pentamerous, with distinctly keeled calyx lobes projecting fromthe hypanthium, clawed and cucullate emarginate petals, antepetalous stamens,and a pentagonal floral disk that fills the hypanthium. Theirphylogenetic position was evaluated using a molecular scaffold approachcombined with morphological data. The results indicate that the flowers aremost like those of extant ziziphoid Rhamnaceae. The associated leaves, assignedto Suessenia grandensis gen. et sp.nov. are simple and ovate, with serrate margins and three acrodromous basalveins. They conform to the distinctive leaves of some extant Rhamnaceae in theziziphoid and ampelozizyphoid clades. As the first unequivocal megafossilevidence of Rhamnaceae in the Southern Hemisphere, these fossils show thatRhamnaceae had expanded beyond the tropics and were present in southern SouthAmerica by the earliest Paleocene. Given previous reports of rhamnaceous pollenin the late Paleogene and Neogene of Antarctica and southern Australia, this newoccurrence increases the possibility of high-latitude dispersal of this family betweenSouth America and Australia via Antarctica during the Cenozoic.