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

ABSTRACT

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 present a 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.

KEYWORDS:

• Dicroidium flora
• Heidiphyllum
• Cuticular analysis
• Gondwana
• Ginkgoales
• Hamshawviaceae

Acknowledgments

We thank the guest editors Christine Strullu-Derrien (London), Paul Kenrick (London), and Thomas Servais (Lille) for the invitation to contribute to this special issue; we gratefully acknowledge the constructive comments and suggestions from two anonymous reviewers.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Author contributions

J.U. prepared the material; J.U., M.M., and B.B. screened and documented the material; all authors contributed to the analysis and interpretation of the data and to manuscript preparation.

Additional information

Funding

This work was supported by the Deutsche Forschungsgemeinschaft (DFG) under Grant BO3131/1 (Emmy Noether project “Latitudinal Patterns in Plant Evolution”) to B.B. and by the Vetenskapsrådet (VR) under Grant 2018-04527 to S.M.; Deutsche ForschungsgemeinschaftDeutsche Forschungsgemeinschaft.