The fossil genus Xylopteris was conceived for Corystospermales fronds presenting pinnate and basally bifurcate pinnae bearing narrow one-veined segments. Later, the possibility was proposed that some of its forms may include 2–3 bifurcated fronds with lobed pinnules and more complex venation. The fossil record attests to its exclusive occurrence in Middle-Upper Triassic Dicroidium floras from Gondwana. Among these, a significant portion of Xylopteris-related morphotypes was included either in the genus Dicroidium or as its subgenus. Such taxonomic placement was adopted in previous studies in Brazil. The new morphotypes herein described present an unsuspected diversity marked by well-preserved frond impressions accompanied by partially preserved Umkomasia strobili. They were identified in a limited exposure of lacustrine shales, at the top of the main fluvial succession of the Passo das Tropas Member, the lower lithostratigraphic unit of the Santa Maria Formation, in the Paraná Basin succession. Given the absence of anatomical structures, the proposed affinity with Xylopteris is based on the original characteristics assigned in the emended diagnosis and in comparisons with other Gondwana records. The described materials attest to the presence of widely distributed types, such as X. elongata, X. spinifolia, X. remotipinnulia and X. rigida as well as X. densifolia, which is restricted to South America and Africa. X. rotundipinnulia, a new generic combination and new species, is proposed for material from Southern Brazil and is comparable to that found in the Molteno beds. The obtained data expands the paleogeographic distribution of the genus and extends the age of the Dicroidium flora in Southern Brazil to the Carnian.
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Vol. 53 • No. 5