The cycads are an ancient group of seed plants. Fossil stems assigned to the Cycadales are, however, rare and few descriptions of them exist. Here, a new genus of cycad stem, Wintucycas gen. nov., is described on the basis of specimens found in the Allen Formation (Upper Cretaceous) at the Salitral Ojo de Agua locality, Río Negro Province, Argentina. The most remarkable features of Wintucyas are: a columnar stem with persistent leaf bases, absence of cataphylls, a wide pith, medullary vascular bundles, mucilage canals and idioblasts; a polyxylic vascular cylinder; inverted xylem; and manoxylic wood. The new genus was included in a phylogenetic analysis and its relationships with fossil and extant genera of Cycadales were examined. In the resulting phylogenetic hypothesis, Wintucycas is circumscribed to subfamily Encephalartoideae, supporting the existence of a greater diversity of this group in South America during the Cretaceous. © 2012 The Linnean Society of London, Botanical Journal of the Linnean Society, 2012, 170, 436–458.

We describe a new species of an ornithischian dinosaur, Isaberrysaura mollensis gen. et sp. nov. The specimen, consisting in an almost complete skull and incomplete postcranium was collected from the marine-deltaic deposits of the Los Molles Formation (Toarcian-Bajocian), being the first reported dinosaur for this unit, one of the oldest from Neuquén Basin, and the first neornithischian dinosaur known from the Jurassic of South America. Despite showing a general stegosaurian appearance, the extensive phylogenetic analysis carried out depicts Isaberrysaura mollensis gen. et sp. nov. as a basal ornithopod, suggesting that both Thyreophora and neornithischians could have achieved significant convergent features. The specimen was preserved articulated and with some of its gut content place in the middle-posterior part of the thoracic cavity. Such stomach content was identified as seeds, most of them belonging to the Cycadales group. This finding reveals a possible and unexpected role of this ornithischian species as seed-dispersal agent.

Summary The pinnately lobed Aptian leaf fossil Mesodescolea plicata was originally described as a cycad, but new evidence from cuticle structure suggests that it is an angiosperm. Here we document the morphology and cuticle anatomy of Mesodescolea and explore its significance for early angiosperm evolution. We observed macrofossils and cuticles of Mesodescolea with light, scanning electron and transmission electron microscopy, and used phylogenetic methods to test its relationships among extant angiosperms. Mesodescolea has chloranthoid teeth and tertiary veins forming elongate areoles. Its cuticular morphology and ultrastructure reject cycadalean affinities, whereas its guard cell shape and stomatal ledges are angiospermous. It shares variable stomatal complexes and epidermal oil cells with angiosperm leaves from the lower Potomac Group. Phylogenetic analyses and hypothesis testing support its placement within the basal ANITA grade, most likely in Austrobaileyales, but it diverges markedly in leaf form and venation. Although many Early Cretaceous angiosperms fall within the morphological range of extant taxa, Mesodescolea reveals unexpected early morphological and ecophysiological trends. Its similarity to other Early Cretaceous lobate leaves, many identified previously as eudicots but in some cases pre‐dating the appearance of tricolpate pollen, may indicate that Mesodescolea is part of a larger extinct lineage of angiosperms.