Sphenobaiera insecta from the Upper Triassic of South Australia, with a clarification of the genus Sphenobaiera (fossil Ginkgophyta) and its delimitation from similar foliage genera

Upper Triassic deposits of the Leigh Creek Coal Measures in South Australia yield exquisitely preserved plant fossils of a typical mid- to high-latitude Gondwanan flora. Here, we presenta detailed cuticular analysis of the ginkgoalean leaf Sphenobaiera insecta J.M. Anderson et H.M.Anderson nov. emend., which is characterized by an unlobed or once-lobed, elliptic to oblanceolate lamina, abundant round to fusiform resin bodies, and absence of interveinal striae. We also propose an emendation to the genus diagnosis so that Sphenobaiera encompasses also unlobed leaves such as most of those attributed to S. insecta. Such leaves may be distinguished from morphologically similar co-occurring leaf taxa, such as Heidiphyllum elongatum (Pinales) and Rochipteris spp. (Petriellales), based on the characteristic resin bodies and sporadic occurrence of vein dichotomies in the central lamina. Sphenobaiera insecta leaves show common evidence of a particular type of herbivory damage along the leaf margin in the form of small (1–1.5-mm-long) semi-circular patches each lined by a crescent-shaped, darkened reaction rim.This work was supported by the DeutscheForschungsgemeinschaft (DFG) under Grant BO3131/1(Emmy Noether project “Latitudinal Patterns in PlantEvolution”) to B.B. and by the Vetenskapsrådet (VR) under Grant 2018-04527 to S.M.;