Leaf phenology, paleoclimatic and paleoenvironmental insights derived from an Agathoxylon stem from the Middle Jurassic of Xinjiang, Northwest China
Xu‐Dong Gou, Hai‐Bo Wei, Yun Guo, Shiling Yang, Zhuo Feng
Abstract
Fossil wood serves as a natural data source for deciphering plant physiological features and paleoclimatic and paleoenvironmental conditions experienced during its lifespan. Although permineralized conifer wood commonly occurs in the Jurassic of Xinjiang Uygur Autonomous Region (Xinjiang), Northwest China, their physiological features and paleoclimatic and paleoenvironmental significance have been rarely studied. Here, we quantitatively analyzed the anatomical characteristics of a permineralized conifer stem (Agathoxylon sp.) from the Middle Jurassic Xishanyao Formation in Naomaohu Town of Yiwu County, Hami City, Xinjiang. The fossil stem is only preserved with secondary xylem. The secondary xylem is pycnoxylic and exclusively composed of tracheids and parenchymatous rays. Tracheids have mostly uniseriate or biseriate, partially triseriate or tetraseriate, alternately or sub-oppositely arranged bordered pits on their radial walls. Rays are mostly uniseriate, partially biseriate, and are up to 27 cells high. There are 4 to 11 cupressoid pits in each cross field, arranged in the araucarioid type. Growth rings are distinct and wide. The mean sensitivity and ring markedness index analyses of growth rings suggest that a stable paleoclimate with regular seasonal fructifications could have prevailed in the Santanghu Basin during the Middle Jurassic. Statistical analyses of cell diameters in 11 successive growth rings indicate that this fossil plant was deciduous. Our study sheds new light on leaf phenology and paleoclimatic and paleoenvironmental conditions of Middle Jurassic conifer plants.