Article: Callistophytalean pteridosperms from Permian aged floras of China

Recent investigations into Permian aged floras from China have highlighted the widespread occurrence of callistophytalean pteridosperms that challenge previous understanding of their spatial and temporal distribution and diversity. In China, the group spans the Permian period and constitutes a distinctive but rare component in many peat-forming environments. The stratigraphically earliest callistophytalean occurs in the Asselian-Sakmarian stages with fossils from the Taiyuan Formation of northern China including ovules of Callospermarion undulatum in coal ball assemblages, and ovulate fronds of Norinosperma shanxiensis and synangiate fronds of Norinotheca shanxiensis in adpression assemblages. More abundant in the fossil records are adpression remains from the Roadian-Wordian stages with the Lower Shihhotse Formation preserving abundant vegetative and ovulate remains of Emplectopteris triangularis that is now considered to represent a callistophytalean. The youngest callistophytalean recognised is from the Wuchaipingian-Changhsingian stages with the Xuanwei Formation of southern China containing a single stem of Callistophyton boyssetii that provides indisputable evidence of the group in the lead up to the end-Permian mass extinction. These accounts are augmented by analysis of pollen records that demonstrate the callistophytalean pollen genus Vesicaspora to be widespread through palynological assemblages from the Permian period in both North and South China, including the Upper Shihhotse Formation, Shihchienfeng Group, Xuanwei Formation, and possibly also in the mid-Pennsylvanian Benxi Formation. Although macrofossil specimens are uncommon elements in the assemblages that contain them, they demonstrate the continuity of callistophytalean pteridosperms from the Pennsylvanian sub-period into the early Guadalupian epoch of the Permian in North China and into the Lopingian epoch of the Permian in South China. Of the species present, both Callistophyton boyssetii and Callospermarion undulatum are known from the Pennsylvanian–earliest Permian age floras of Euramerica, whereas Norinosperma, Norinotheca and Emplectopteris appear to represent endemic Cathaysian elements. Results imply that callistophytalean pteridosperms can no longer be excluded from theories of post-Carboniferous plant evolution and floristics, appearing to have played an important role in both Permian and Carboniferous aged plant communities. The presence of Vesicaspora in several formations from which macro-remains have not been identified is a hopeful indicator that further callistophytalean pteridosperms are yet to be found.