ESTUDIO ANATOMICO DE UN ESTIPITE PETRIFICADO DE "OSMUNDITES", DE EDAD JURASICA, PROCEDENTE DEL GRAN BAJO DE SAN JULIAN, PROVINCIA DE SANTA CRUZ

Abstract

An anatomical study of a Jurassic petrified Osmundites stem, from the Gran Bajo de San Julian, Santa Cruz Province. A few silicified fragments of a stem from La Matilde Formation (Jurassic) have proved to belong to a new species of Osmundites, 0. patagonica. In the same locality, sterile fronds of CladophlebiS patagonica Frenguelli are present. The good· preservation of the material enabled the authors to study the vascular cylinder and the different" tissues present in the leaf bases. Abortive leaf bases and roots have alSo been sfudied.. This new species is based mamly on the different pattern presented by the distribution of mechanical tissue in the petioles. The evolution Of the stelar types of fossil Osmundaceae is considered, starting with the typical protostelic found in Palaeozoic representatives of this group, and going through the transitional protostelic-siphonostelic-dictyostelic types. Finally, the systematic position and affinities of 0. patagonica are considered.