A new conifer stem, Ductoagathoxylon tsaaganensis, from the Upper Permian of the South Gobi Basin, Mongolia and its palaeoclimatic and palaeoecological implications

Abstract

Permineralised stems of Ductoagathoxylon tsaaganensis Cai, Zhang et Feng sp. nov. are described from the Upper Permian strata of the Tsaagan Tolgoy section, South Gobi Basin, Mongolia. The stems were preserved with pith and primary and secondary xylems. The pith is solid, heterocellular, and characterised by regularly arranged clusters of secretory cells at the periphery. The primary xylem is the endarch and mesarch. The tracheid walls exhibited annular, helical, and scalariform thickening from the protoxylem to metaxylem. The secondary xylem is of the Agathoxylon-type and is composed of tracheids and parenchymatous rays. The growth rings of the stems were distinct, with broad earlywood and narrow latewood. Radial tracheid pits in the secondary xylem are contiguous and alternately arranged, uni- or biseriate in the latewood, and bi- to tetraseriate in the earlywood. Rays are uniseriate and 1–7 (mostly 2–4) cells high. Each cross-field possessed 1–19 (mostly 3–9) cupressoid pits. Quantitative analysis of the growth rings indicated that the plant was likely a deciduous conifer that lived in a seasonal, temperate, and wet climate. However, a growth interruption with inflated cells was present in the secondary xylem, indicating that the tree had survived climatic damage, probably an early spring cooling event. Fungal remains, including hyphae and spores, and evident white-rot patterns in the stems revealed a common occurrence of fungal infections in the ecosystem. Our study sheds new light on the plant diversity and climatic and ecological features of the Angara flora during the Late Permian in the South Gobi Basin.