Contribución a la paleoxiloflora de la Formación Yaguarí, Pérmico Superior de Uruguay

Resumen

This paper is a further contribution to the study of the xyloflora of the Upper Permian Yaguarí Formation, from several localities of the Cerro Largo Department, Uruguay. The following taxa are described: Australoxylon teixeirae Marguerier, Zalesskioxylon uniseriatum Pant y Singh, Zalesskioxylon sahnii (Singh) Lepekhina and Araucarioxylon nummularium (White) Maheshwari. The validity of the diagnosis of Australoxylon, a genus found in several formations, is considered and a short analysis of the different species assigned to it is included. This genus is characteristic of the Gondwanic flora due to its limited stratigraphic record and its peculiar anatomical structure. The picnoxylic secondary woods studied here show typical anatomical characters for Paleozoic woods, but have uniseriate and very short rays, a character considered as more advanced; also a reduction in the seriation of pits on the tracheidal walls and mixed and abietinean pits are registered. An evolutive analysis of them indicates an intermediate position between primitive Paleozoic forms and more evolved Mesozoic ones. A comparison with other Gondwanic contemporary formations permits to confirm the Upper Permian age assigned to the Yaguarí Formation. The assemblage also allows to infer hydromesophytic to mesoxerophytic climatic conditions, while the analysis of the growth rings suggests the absence of low temperatures for the period.