Eduardo G. Ottone

A lower triassic miospore assemblage from the Puesto Viejo formation, Argentina

Abstract Twenty-three species of miospores, distributed among 16 genera have been recovered from the basal section of the Puesto Viejo Formation, near San Rafael City, Mendoza Province, Argentina. The sequence is dated as Early Triassic on the evidence of fossil vertebrates. One new species, Aratrisporites spongeosus sp. nov., is erected and three new combinations, Verrucosisporites margaritatus (Madler) comb. nov., Pteruchipollenites gondwanensis (Jain) comb. nov. and Pteruchipollenites argentinus (Jain) comb. nov. are affected. The miospore assemblage is characterised by a low diversity and relative abundance of spores and haploxylonoid bisaccate pollen grains. It suggests that the parent palaeoflora consisted of a fairly low number of hydrophyllous plants growing under humid temperature climatic conditions. The palynological data support the early Triassic age assignment.

Chlorococcalean algae as palaeoenvironmental indicators: new data from the Los Rastros Formation, Triassic of central-western Argentina

Chlorococcalean algae as palaeoenvironmental indicators: new data from the Los Rastros Formation, Triassic of central-western Argentina. Lacustrine strata of the Los Rastros Formation (Triassic) at the Ischigualasto Provincial Park section, San Juan province, yield a distinctive palynological assemblage of miospores and Chlorococcalean algae. The miospore association is characterized by a relative abundance of corystosperm pollen grains with subordinate spores and inaperturates, diploxylonoid disaccates, monocolpates, monosaccates and striate pollen grains. The phytoplankton is represented by the Chlorococcalean Botryococcus and Plaesiodictyon. Geological data and variations in phytoplankton content indicate that the lacustrine system should be moderately eutrophic towards the lower third of the section, evolving into a body with oligotrophic conditions through the middle and upper part of the unit. Comparisons with the Rio Gualo section suggest palaeoenvironmental similarities between the two areas. One new disaccate pollen grain species, Platysaccus rhombicus, is proposed.

Reconstruction and Phylogenetic Significance of a New Equisetum Linnaeus Species from the Lower Jurassic of Cerro Bayo (Chubut Province, Argentina)

Abstract. We describe Equisetum dimorphum sp. nov. from the Lower Jurassic of Chubut Province, Patagonia, Argentina. This new species Is based on fertile and vegetative remains preserved as Impressions of stems, leaves, strobili, transversal sections of the stems showing their anatomy, and terminal pagoda-like structures. The fine-grained sedimentary matrix also preserved detailed Impressions of epidermal features. The morphological characters allow a whole-plant reconstruction and assignment to Equisetum. Equisetum dimorphum sp. nov. shows a mosaic of morphological characters that are commonly present in other Mesozoic forms and representatives of the two extant Equisetum subgenera, e.g., sunken stomata and a blunt strobilus apex. Compared to other well-known Mesozoic equisetalean taxa, Equisetum dimorphum sp. nov. appears to be most closely related to a group of Jurassic Equisetum-like plants including Equisetum laterale Phillips and Equisetites ferganensis Seward. Additional evidence for the morphological stasis of the fertile and vegetative organs of extant horsetails is supplied with this new material, adding further support to the hypothesis that the extant horsetails are a successful group that has undergone only little morphological changeover time and that has been present, nearly worldwide, since Jurassic times.