Taxonomic investigations on permineralized conifer woods from the Late Paleozoic Angaran deposits of northeastern Inner Mongolia, China and their palaeoclimatic significance

A diverse fossil conifer wood assemblage was described from the Late Paleozoic Angaran deposits in Inner Mongolia (=Nei Mongol) of northeastern China. The fossil wood materials were collected from the Upper Carboniferous Baoligemiao Formation in Sunitezuo Qi and the Middle Permian Zhesi Formation in Xi Ujimgin Qi, northeastern Inner Mongolia, including four species. Among them, Sinopalaeospiroxylon baoligemiaoense gen. et sp. nov. represents a new taxon of secondary xylem with Araucarioid-type and transitional type of radial wall pitting, and tertiary taxoid spiral thickenings. It is characterized by the pinioid pitting and nodular thickening on the end wall on the horizontal wall of rays. Sclerospiroxylon neimongolense sp. nov. is represented by a xylem cylinder containing the secondary and primary xylem and pith. The tracheids on the radial wall yield Araucarioid-type pitting as well as a taxoid tertiary spiral thickening. The primary xylem is of endarch, and the pith consists of heterogenous cells. The sclerochyma cells are scattered among the parenchymatous tissues. Zalesskioxylon zhesiense sp. nov. is a wood species with very similar anatomical features to those of the genus Araucarioxylon. It differs, however, in having simple and no-bordered cross-filed pitting in Z. zhesiense. Chapmanoxylon xiugiense (Zhang and Zheng) comb. nov. is recognized based upon wood xylems containing Araucarioxylon-type secondary xylem, endarch primary xylem and a pith yielding homogenous parenchyma cells. These conifer wood taxa show more or less growth rings in the secondary xylem. Such fossil woods from the Late Paleozoic deposits of northeastern Inner Mongolia imply a warm moderate vegetation type. It is a composition part of the Northern Biogeographic Realm in China showing seasonal variation of the palaeoclimate.