Fossil flowers from the early Palaeocene of Patagonia, Argentina, with affinity to Schizomerieae (Cunoniaceae)

ARI IGLESIAS; GANDOLFO, M. A.; JUD, N.A.; WILF PETER

ANNALS OF BOTANY

OXFORD UNIV PRESS

Lugar: Oxford; Año: 2018 vol. 121 p. 431 - 442

0305-7364

Background and Aims Early Paleocene plant fossils from Patagonia provide insights into the recovery from the end-Cretaceous extinction and the history of Cenozoic floristic change in South America. Actinomorphic flowers from the  early Paleocene (Danian) of Patagonia, Argentina with 8?10 perianth parts are described and evaluated in a phylogenetic framework. The goal of this study is to determine the identity of these fossil flowers and to discuss their evolutionary, paleoecological, and biogeographic significance. Methods More than 100 fossilized flowers were collected from three localities in the Danian Salamanca and Peñas Coloradas formations in southern Chubut. They were prepared, photographed, and compared to similar extant and fossil flowers using published literature and herbarium specimens curated in the Bailey Hortorium at Cornell University. Phylogenetic analysis was performed using morphological and molecular data. Key results The fossil flowers share some but not all the synapomorphies that characterize the tribe Schizomerieae within Cunoniaceae. These features include the shallow floral cup, variable number of perianth parts arranged in two whorls, elaborate laciniate petals, anthers with a connective extension, and a superior ovary with free styles; however, the number of perianth parts is doubled and the in-situ pollen preserved in the anthers is tricolporate, with a surface is more like that of other Cunoniaceae outside Schizomerieae such as Davidsonia or Weinmannia.  Conclusions We recognize a new extinct genus in the Cunoniaceae. The fossil taxon belongs within crown-group Cunoniaceae, along the stem lineage leading to Schizomerieae. Extant relatives are typical of tropical to southern-temperate rainforests, suggesting that these fossils might indicate a similarly warm and wet paleoclimate consistent with other indicators from the Salamanca Formation. The oldest reliable occurrence of the family is based on fossil pollen and wood from the Late Cretaceous of the Antarctic Peninsula and Chubut Province, Argentina, whereas in Australia it dates to the late Paleocene. This discovery demonstrates that the family survived the Cretaceous-Paleogene boundary event in Patagonia and that diversification of extant lineages in the family was underway at least by the earliest Cenozoic.