Novos registros de angiospermas pleistocênicas para formação Rio Madeira, bacia do Abunã, Rondônia, Brasil

Abstract

Paleobotany is an interdisciplinary science in which botany and geology are interconnected in the study of fossil plants, aiming at the reconstruction of isolated and / or fragmented phytofossils and the knowledge about the relationship between fossil and current plants, as well as their evolutionary trajectory. Due to the abundance of fossil leaves in a fossil assemblage, taxonomic classification methodologies were developed based on leaf architecture, and these characters are widely used to establish paleoenvironmental inferences based on the relationship of leaf physiognomy characteristics with environmental variables. Thus, the objective of the present work is to define the leaf architecture pattern of fossil angiosperm leaves from the Upper Pleistocene of the Abunã Basin, establishing its systematic and taxonomic affinities, and thus contribute to the characterization of the paleobiodiversity of the study area the along the Upper Pleistocene. The materials come from the area covered by the Jirau DAM, Rondônia State, collected at the Estaca 93 Outcrop, Rio Madeira Formation, Abunã Basin. The leaves were analyzed in a stereomicroscope with the aid of a caliper for measurements. For graphic documentation, macrophotographs with digital camera and stereomicroscope microphotographs were obtained. The photographs were redrawn (line drawing) to detail the venation pattern to the preserved order. The description of leaf architecture followed the terminologies proposed in the Manual of Leaf Architecture, and to carry out the identification to the possible taxonomic level. The materials were compared with specimens already described in paleobotanical literature and in current botanical inventories. The results show the description and botanical affinity of seven leaf specimens of angiosperms, which three of these specimens included only as belonging to the Eudicotyledons, two with affinities to the Moraceae family and two to the Myrtaceae family. The current distribution and the environmental tolerance of these families demonstrate that both are more related to regions of a humid tropical climate, which has been confirmed based on the preserved morphological details. Therefore, our data corroborate with other studies carried out with paleoflora from the Amazon context, which infer the presence of a tropical forest and a climate like the current one in the Upper Pleistocene.