A NOVEL CONIFEROUS TREE TRUNK WITH SEPTATE PITH FROM THE GUADALUPIAN (PERMIAN) OF CHINA: ECOLOGICAL AND EVOLUTIONARY SIGNIFICANCE

A novel coniferous tree trunk, Plyophyllioxylon hulstaiense gen. nov. et sp. nov., is described from the Lower Shihhotse Formation (Guadalupian, Permian) of the Hulstai coalfield, in the Inner Mongolia Autonomous Region of northern China. The decorticated tree trunk is permineralized and is characterized by broad eustele and well-developed pycnoxylic secondary xylem. The parenchymatous pith is up to 30 mm in diameter, with the central portion septated by diaphragms and the perimedullary cells continuous. The primary xylem is endarch; tracheids from protoxylem to metaxylem possess helical, annular, and scalariform/reticulate thickenings. The monarch leaf traces initiate from the pith margin and are arranged according to a helical phyllotaxy of 3/24 or 4/24. Tracheids in the secondary xylem have uni- to biseriate araucarioid pits; cross field pits are cupressoid. Ray cells are parenchymatous, with smooth walls, uni- to biseriate. Vertically aligned or isolated axial xylem parenchyma is interpreted as an evolutionary adaptation to the increasingly arid local environment. Crystallized or spheroidal storage substances contained in the axial parenchyma also suggest that the local environment had become unstable by at least the Guadalupian. Distinctive coprolites are preserved within the pith chambers, spheroidal or ovoid shaped, 20-50 mu m in diameter, interpreted as a new type of feeding behavior, likely by a detritivorous arthropod.