Terminalia palaeopubescens sp. nov. (Combretaceae) da Formação Fonseca (Eoceno/Oligoceno) de Minas Gerais, Brasil: morfologia foliar, fungos epifilicos associados e paleoclima

Abstract

No presente estudo sao descritas laminas foliares preservadas na forma de incarbonizacoes e impressoes, e fungos epifilicos associados, a partir de material coletado em folhelhos da Formacao Fonseca (Priaboniano/Rupeliano da Bacia de Fonseca, estado de Minas Gerais, sudeste do Brasil). Com base na arquitetura do orgao foliar e caracteristicas do indumento e estabelecida uma nova especie relacionada ao genero tropical moderno Terminalia L. (Combretaceae). A folha de Terminalia palaeopubescens sp. nov. e mesofila, obovada estreita e com margem inteira, nervuras secundarias camptodroma-broquidodromas, terciarias percorrentes mistas predominantemente alternas, quaternarias percorrentes alternas, e as de quinta ordem formam uma rede poligonal regular, com areolas pequenas e bem desenvolvidas. No indumento, apresenta tricomas simples, esguios, pontiagudos e com base intumescida, tipicos da familia Combretaceae. Fungos epifilicos do genero Callimothallus Dilcher (Microthyriaceae), na forma de discos de tamanho variavelmostram ter colonizado grande parte da superficie foliar. Sua presenca, associada a Phragmothyrites Edwards, previamente identificado para a mesma unidade, sugere uma proeminente micoflora associada a vegetacao, sustentada por condicoes predominantemente quentes e umidas. Os dados aqui aportados, analisados conjuntamente com outros indicadores taxonomicos, tafonomicos e da fisionomia foliar, convergem para a presenca de uma densa floresta pluvial, sustentada por abundantes precipitacoes e calor, que se desenvolveu em areas proximas as margens dos sistemas fluviais e planicies de inundacao entre o final do Eoceno e inicio do Oligoceno no sudeste do Brasil. Abstract. TERMINALIA PALAEOPUBESCENS NOV. SP. (COMBRETACEAE), FROM THE FONSECA FORMATION (EOCENE/ OLIGOCENE), MINAS GERAIS STATE, BRAZIL: LEAF ARCHITECTURE, EPYPHYLLOUS FUNGI AND PALEOCLIMATE. In this study, well-preserved leaf-blade compressions and impressions from shale levels in the Fonseca Formation (Priabonian/Rupelian of the Fonseca Basin, state of Minas Gerais, southeastern Brazil) and associated epiphyllous fungi are described. Based on leaf architecture and indumentum, a new species is established, assigned to the extant tropical genus Terminalia L. (Combretaceae). The leaf of Terminalia palaeopubescens sp. nov. is mesophyll, narrow obovate and with an entire margin. Its secondary veins are camptodromous-brochidodromous, the tertiary pattern is percurrent mixed predominantly alternate, the quaternaries are alternate percurrent and the higher orders regular polygonal reticulate, with small and well developed areoles. Trichomes are present in the indumentum and are simple, slender, pointed, and with a swollen base, typical of the Combretaceae. Epyphyllous fungi, in the shape of microthyrioid disks of variable size and profusely colonizing the leaf surface, were assigned to Callimothallus Dilcher (Microthyriaceae). The presence of those biogenic structures (besides Phragmothyrites Edwards, already reported in the same levels of the Fonseca Formation) indicates that a prominent leaf mycoflora was associated to the vegetation, probably sustained by warm and humid conditions. The data here presented, analyzed together with other taxonomic, taphonomic and foliar physiognomic indicators, lead to the hypothesis that a dense rainforest, supported by heavy rainfall and high temperatures, was thriving near the banks and floodplain environments associated to fluvial systems of the Fonseca Formation, during the Eocene/Oligocene transition, in southeastern Brazil.