New species of Protaxodioxylon (conifer wood) from the Middle Permian of the Metangula Graben (Niassa Province, Mozambique) and their implications

Abstract

We describe for the first time in precise anatomical detail new occurrences of petrified woods in the K5 formation of the Metangula Graben (Niassa, northern Mozambique), pertaining to the Capitanian (mid Permian). The two new species of fossil wood are described from two very well-preserved specimens. The two new species, Protaxodioxylon verniersii sp. nov. and Protaxodioxylon metangulense sp. nov. are characterized by showing tracheids with mixed radial pitting and taxodioid pits in the cross-field, typical of the genus Protaxodioxylon. The specimens described are mostly distinguishable from other Protaxodioxylon species by the absence of axial parenchyma, the height of rays and the number of pits per cross-field. Protaxodioxylon species reported to date were mostly restricted to the Northern Hemisphere and to the late Mesozoic (Jurassic and Cretaceous). Surprisingly, however, this study infers that this fossil wood genus has a significantly longer time range than previously thought and underwent dispersal and diversification even earlier during the Palaeozoic. Additionally, both specimens display distinct growth rings indicating that the fossil woods grew in an environment controlled by seasonal variation with partial suspension of growth in times of less water availability and/or lower temperature. On the other hand, the occurrence of Protaxodioxylon suggest a humid temperate, warm subtropical climate condition during the Capitanian in the Metangula Graben.