Caules de sphenophyta da formação Rio do Rasto (Bacia do Paraná, permiano superior)

Rosemarie Rohn, Oscar Rösler

Resumo


Sphenophyte stems have been studied from 28 new outcrops of the Rio do Rasto Formatian (Passa Dois Group, Paraná Basin, Upper Permian) in Paraná and Santa Catarina States. Four new, informally described species of Paracalamites are recognized, each corresponding to a different basic morphologic stem type. Paracalamites sp. 1, P. sp. 2 and P. sp. 3 are preserved as pith cavity casts, probably having calamitacean affinities. These species exhibit well-preserved fascicular and interfascicular áreas and are differentiated by their respective cellular patterns in interfascicular áreas (corresponding to the medullary rays), nodal region characteristics and morphometric values. Many features considered important in these species are not inciuded in the diagnoses of Paracalamites australis Rigby and P. levis Rigby, the two species in which practically ali isolated sphenophyte pith cavity casts from Gondwana are generally placed. Paracalamites sp. 2 and P sp. 3 present internai evidence of branch insertions. Paracalamites aff. P. sp. 1 shows possible "Williamson infranodal canais". Some internai casts of Paracalamites sp.2 are covered by thin films (molds) exhibiting cell impressions, which probably represent more externai tissues of the stem. "Paracalamites" sp.4 is mainly characterized by externai surface features, including possible leaf sheaths, in one case intimately associated with the pith cavity cast. This species is similar only to stems from Lidgetton (South Africa), as yet not formally classified, supposedly having equisetacean rather than calamitacean affinities. The South African stems, some stems of Phyllotheca indica Bunbury and those reported in this paper are the only reasonably well preserved and adequately described Gondwanic sphenophyte stems. Detailed studies of more carefully collected material will probably provide many clues as to the evolution and systematics of the Sphenophyta

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DOI: http://dx.doi.org/10.11606/issn.2316-8986.v17i0p39-56

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