Micromorphological evaluation of the Bennettitales – a key group of extinct Mesozoic gymnosperms
Christian Pott
The resolution of broad-scale seed plant relationships has reached an impasse owing to the inability of molecular techniques to evaluate the relationships of extinct groups, and uncertainties in the coding of character states for many incompletely preserved fossil groups. Phylogenies constructed on the basis of molecular data commonly invoke different relationships to those based on morphological data from living and fossil plants. Advances in our understanding of seed plant phylogeny must now depend on obtaining new and better structural data from the many poorly known fossil groups, key among which is BennettitalesThe research project “Micromorphological evaluation of the Bennettitales — a key group of extinct Mesozoic gymnosperms" is funded by a Swedish Natural History Museum postdoctoral fellowship. It follows on from the a PhD study by Christian Pott at the University of Münster on the Late Triassic (Carnian) Lunz flora (Austria) based on more than 3500 specimens.
The project will evaluate the microanatomical characteristics of extinct Bennettitales, a group of Mesozoic gymnosperms that hold a key position within seed plant evolution. Analyses of both sterile and fertile plant remains will be undertaken to resolve questions about the taxonomy, paleobiology and paleoecology of this enigmatic group.
The Bennettitales are enigmatic gymnosperms characterised by complex reproductive structures, some of which are not yet fully understood. The earliest persuasive bennettitalean records come from the Late Triassic but earlier records are possible. The bennettites were one of the most ubiquitous plant groups in the Jurassic but apparently became extinct by the end of the Cretaceous.
Syndetocheilic stomata are typical for bennettitaleans and this character separates them from all other groups of seed plants, including the morphologically similar Cycadales. However, the stomata of some extant Gnetales (Gnetum, Welwitschia), resemble the bennettitalean stomatal type and such features may provide important tools for phylogenetic evaluation. Similarly, the reproductive organs of bennettitaleans are complex, diverse, and show several features that suggest linkages with the Gnetales and angiosperms. This apparent sister-group relationship between Bennettitales and Gnetales/angiosperms requires testing via a fundamental re-evaluation of the morphology and anatomy of bennettites to understand the character variation within the group and homologies with other seed plants.
Specifically, the project involves investigations of bennettite remains from five key regions (Austria ,Skåne ,Iran ,Afghanistanand Australia) using a diverse array of preparatory and analytical techniques. The project will:
• Describe and illustrate the microanatomical (epidermal) characteristics of bennettitalean foliage from a broad range of genera;
• Evaluate which microanatomical characters are useful for taxon discrimination within the Bennettitales and which features may be informative for understanding broader seed-plant relationships;
• Analyse the cuticle and in situ pollen of fertile organs to provide a better basis for fossil plant reconstructions, and to aid resolution of bennettite phylogenetic relationships;
• Determine the paleoecological signatures of bennettites based on regional differences in macromorphological and stomatal characteristics.
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