A new permineralized Araucaria species from the Early Cretaceous of Chubut Province, Argentina

Abstract

The conifer family Araucariaceae is characterized by a relatively small extant diversity, especially comparedwith its rich, diverse and worldwide distribution in the fossil record. Most of the Mesozoic record ofAraucariaceae is confined to the type genus Araucaria, while Agathis and Wollemia records are less abundant.Extant Araucaria is divided into four sections: Eutacta, Bunya and Intermedia have distribution confined toAustralasia, while section Araucaria (i.e., A. araucana and A. angustifolia) is distributed in southern SouthAmerica. Previously described anatomically preserved cones from Argentina are restricted to Araucariamirabilis, from the Middle Jurassic of Patagonia. Here we describe a new permineralized seed cone fromthe Lower Cretaceous Cerro Barcino Formation (Chubut Province, Patagonia, Argentina). The cone ischaracterized by a broad central axis, composed of parenchymatous and isodiametric sclerenchymatic cellsthat are more abundant towards the periphery of the axis. The parenchymatous pith is surrounded by aring of isolated, endarch vascular strands. A series of resin canals occur on the outside of the stele, theseare highly variable in shape and morphology. Numerous fan-shaped bract/scale complexes are helicallyarranged around the central axis, each bearing a single, anatropous, central ovule completely covered bytissues of the ovuliferous scale. Megagametophyte and integuments were observed in some seeds. Thisbract/scale complex morphology is characteristic of araucarian conifers. The new cones from Patagonia arecharacterized by a bract/scale complex with highly reduced lateral wings; a feature that can be consideredas an intermediary stage in the evolution of the South American section of the genus Araucaria, whereextant species are characterized by the absence of lateral wings on their bract/scale complexes. This newspecies shows a possible intermediate stage in the evolution of the genus Araucaria in South America, whileits phylogenetic position and importance is investigated on the base of a total evidence analyses.