Systematic and organ relationships of Neocalamites (Halle) Vladimirovicz, and Nododendron (Artabe and Zamuner) emend. from the Triassic of Patagonia. Palaeobiogeographic, palaeoenvironments and palaeoecology considerations

Abstract

We present descriptions of Neocalamites carrerei and Nododendron suberosum (Equisetales incertae sedis) from the Cañadón Largo Formation (late Ladinian–early Carnian), Deseado Massif, central Patagonia, Santa Cruz Province, Argentina. Descriptions are based on moulds and impressions of vegetative stems, leaf whorls and nodal diaphragms, and of a reproductive structure. These specimens enable a critical re-evaluation of morphological and anatomical features that have been historically used to define these two problematic genera, including node-type, leaf-base morphology, vascular cylinder of the nodal diaphragm. We suggest, that the diagnosis of Neocalamites (Halle) Vladimirovicz must be used when vegetative organs are described with or without reproductive structures in organic connection or in co-occurrence. We propose the emendation and revalidation of the genus Nododendron by nomenclatural priority over Zonulamites. Distinctive morphological-anatomical characters of Nododendron and Neocalamites are established. The different plant organs of the equisetalean species were found dispersed in the same beds of the Cañadón Largo Formation, allowing to establish plant organ affiliation by morphological-anatomical correspondence and co-occurrence. Neocalamites carrerei is the best represented equisetalean species in the Triassic of Gondwana. Nododendron suberosum is widespread in the Middle–Upper Triassic of Argentina, South Africa and Antarctica. The herbaceous-shrubby Neocalamites carrerei and the shrubby-arborescent Nododendron suberosum were successful extensive monotypic populations that developed on the margins of channels, margins of bodies of water, on well-drained banks and in the humid, inundated areas and/or water-saturated soils of the floodplain by clonal growth.