Current research and research interests
(1) Aiming to understand the evolutionary history of the cycadophytes with emphasis on the Mesozoic Bennettitales (Williamsoniaceae) and their systematic position, taxonomy, anatomy, biology, ecology and role in contemporary ecosystems
(2) Investigating the worldwide biogeography of Bennettitales to understand their diversification and decline as well as identifying their potential provenance
(3) Testing the hypothesis that the rise of the angiosperms resulted in suppression, refugial retreat or extinction of key Mesozoic gymnosperm groups (Cycadales, Bennettitales, Nilssoniales, Ginkgoales)
(4) Clarifying the still ambiguous status and systematic position of another group of cycadophytes, viz. the Nilssoniales, and their architecture, biology and ecology
(5) Evaluating the tree-architecture of gymnosperms across all groups with regard to potential development of particular growth habits by certain groups and their ecological implications
Particular research on these groups will provide insights that have the potential to affect the current phylogenetic relationships of seed plants and will, over the coming 5-10 years, result in a reassessment and refinement of the characters deployed in seed plant phylogeny.
Primary research project
My current project is based on results achieved in my former project completed at the Swedish Museum of Natural History, Stockholm, Sweden (NRM) that aimed to understand the evolutionary history of the cycadophytes and to clarify the potential of this diverse, but poorly understood complex of Mesozoic plants as palaeoenvironmental/palaeoclimatic markers for the Mesozoic. The new project will investigate Arctic fossil floras to assess changes in vegetation and within major gymnosperm lineages during the Mesozoic, analyze biogeographic patterns of Northern Hemisphere Mesozoic floras, test the hypothesis that the rise of the angiosperms resulted in suppression, refugial retreat or extinction of key Mesozoic gymnosperm groups (Cycadales, Bennettitales, Nilssoniales, Ginkgoales), and finally assess specific plant adaptations to high-latitude habitats of Mesozoic greenhouse climates using micro-morphological and micro-anatomical traits and general plant architecture.
The research involves reconstructions of whole-plant-taxa that serve as natural units for improved phylogenetic analyses, evaluation of the temporal and spatial diversity and diversification of cycadophytes to reveal evolutionary patterns in fertile and sterile structures. In addition, the assessment of cuticular and anatomical adaptations may be useful for interpreting local environmental to regional climatic conditions for these plants during the Mesozoic. The project focuses on two enigmatic groups of extinct cycadophytes, i.e. the Bennettitales and the Nilssoniales, and on two groups that still have representatives in modern flora, i.e. the Cycadales and the Ginkgoales.
ad (1)--Currently, I am addressing the circumscription and demarcation of the Williamsoniaceae, a subordinate 'taxon' of Bennettitales that is most likely polyphyletic incorporating several morphotaxa that may not be closely related. Considerable research on this group as an entity has not been conducted during the past 120 years and neither has this group been placed into any ecological context. In a revision of the original material of Wielandiella angustifolia, the most influential member of this group, I achieved a different view on its reproductive biology, substantiated its influential 120-year-old reconstruction by a considerable number of new anatomical details, and placed the plant for the first time into an ecological context. However, the analysis also disclosed a strong need of further investigation of the group. Key fossils for this research originate from the Rhaetian of Scania and the Bajocian of Yorkshire, a substantial number of which is stored in NRM, that will now be subjected to more in-depth investigations in order to reveal more insights in the relationships of this group to the evolution of the angiosperms. Mechanisms (such as ecology, tectonics, etc.) that influenced the distribution of the Bennettitales have not been studied in a biogeographic context. Results gained from this part of the project may also assist the geographic search profile for early angiosperms or to reveal possible mechanisms that contributed to angiosperm radiations. My project traces bennettitalean taxa through time and space and assesses possible ecological and climatic signals from these distributional patterns that will aid interpretations of Mesozoic terrestrial environments.
ad (2)--The origin of Bennettitales is still obscure; they were cosmopolitan not only during their evolutionary heyday in the Late Jurassic/Early Cretaceous, but already by the Carnian. The large geographical range of my previous research provides me now with a very good overview of the spatial and temporal distribution of the group. I was able to show that several intriguing records from the Permian of China and Russia and from the Paleogene of Australia and Greenland suggest an expanded temporal range and survival into the Paleogene in high-latitude refugia, but distributional data for the oldest and youngest bennettitaleans is indeed poor. Collections from the Permo-Carboniferous of China provide an excellent basis for this part of the project, because the oldest cycadophytes hitherto known originate from that area and period. Locating the oldest Bennettitales will facilitate targeted field collections. Even information on the anatomy and reproductive biology of the oldest (viz. Carnian) known bennettites is incomplete, which is evident from my previous and ongoing studies of the cycadophyte reproductive structures from the Lunz flora, of some of which I could recently reveal the full potential for further assessment of the phylogenetic relationships among seed plants. Very recently, I have been included in a research project on Permian compression fossils from Jordan, among which are potential Bennettitales, which then are in fact the oldest representatives of that group.
ad (3)--In the Mesozoic greenhouse world, so-called 'paratropical environments' at high northern latitudes played a crucial role for the development, diversification and survival of major plant groups. High latitudes may have provided refugia for plant groups that could not compete with the rapidly radiating angiosperms (flowering plants) at lower latitudes in the mid-Cretaceous. For a better understanding of Mesozoic fossil floras from the Arctic, I will assess the changing composition of the vegetation in northern Europe during the Late Triassic-Early Cretaceous. Further, the impact of angiosperms on previously dominating plant groups, such as cycadophytes and ginkgophytes, will be investigated. The focal area includes Ellesmere Island, Greenland, Norway (Andøya, Trondheim), Svalbard and Franz-Josef-Land, an area called here the 'Nordic Arctic'.
ad (4)--Nilssoniales is a group that is usually considered a member of the cycads. However, the architecture, biology and ecology of Nilssoniales depict in my view a separate plant group. A consensus on the placement of Nilssoniales is still lacking and a thorough revision of Nilssoniales and related seed plants is thus warranted. Therefore, I will focus on a revision of both published and new material (involving extensive collections-based work and cuticular analysis whenever possible) rather than a simple re-evaluation and re-scoring of characters on the basis of the published accounts.
ad (5)--Some Bennettitales apparently developed a particular plant architecture (divaricate growth habit) that is unique amongst gymnosperms, except for a small group of isolated araucarian endemics to New Caledonia. While tree-architecture models are generally well studied in modern angiosperms, an analogue analysis for gymnosperms has never been conducted, probably due to the dominating monopodial growth form in the group. Divaricate growth habit in modern plants is a feature that has been developed under different ecological constraints (e.g. climate, browsing by herbivores). However, whether this is a primary or secondary adaptation, is not unequivocally to ascertain. Due to the specific ecological adaptations of Bennettitales, the particular divaricate growth habit in that group strongly attracted my attention. I am now planning to initiate research on tree-architecture models of fossil and modern gymnosperms within the current year, involving restored whole-plant fossil taxa, to fully assess the potential of this feature for further appraisal of the phylogenetic relationships among seed plants.
Secondary research projects
A smaller project on a Carnian flora from Svalbard that I initiated in 2011 uncovered an unexpectedly high conformity between the Carnian floras of Svalbard and Lunz (Austria), two localities that were separated by 3500 km already during the Upper Triassic. This fact is of high interest concerning the biogeography and origin of Bennettitales (see above). The study resulted in two publications on the revision of the Triassic flora from Svalbard, and I will subsequently work on the revision of Svalbard's Lower Cretaceous flora, whereof the body of the material is stored at NRM, and correlate it with the Wealden from Northern Germany and Europe, whereof a good body of material is stored at MfN. The Wealden is a significant period because it antedates the time period of the major decline of the Bennettitales, whereof the reasons are still unclear, and investigation of floras from this period might find evidence for the expulsion of bennettitaleans to refugial areas. A recent study on freshly collected Lower Cretaceous fossils from Northern Germany revealed that the 'Wealden' of Germany and adjacent areas is in strong need of revision. The small initial study of Carnian fossils thus will turn into a larger-scale project considering Mesozoic floras from the Arctic in relation to those from central Europe, and will become an integrated part of my primary research project outlined above.
Within the framework of another project, I currently investigate, together with colleagues from the Free University Berlin, NIGPAS and the Nanjing University, Nanjing, China, and the Tianyu Museum of Natural History, Pingyi, China, Jurassic and Cretaceous floras from the Daohugou and Jehol biota of Liaoning, Hebei and Inner Mongolia, China. This project involves descriptions and reconstructions of individual plants, but also of the floras and their individual ecologies as a whole.
Besides my work on Mesozoic cycadophytes, I have just completed the cryptogam component (ferns and fern allies) of the Lunz flora. This study revealed that in the Northern Hemisphere, apparently established Palaeozoic taxa co-exist with new and modern fern groups, thus making the Carnian an important period in the evolutionary history of ferns. The work on the Lunz flora is planned to be completed with a book volume to be produced for the Natural History Museum of Vienna, containing a complete description of the Lunz flora.
Recently, I also initiated a research project involving the long since neglected Mesozoic flora of Westphalia, parts of which have been published in 1880 and 1991. A thorough examination and revision of the large amount of studied and unstudied specimens adds perfectly to my main research aims outlined above as floras from the Upper Jurassic (heyday of the bennettites) and the Middle-Upper Cretaceous (sudden successful proliferation of the angiosperms) are known from Westphalia; ongoing exploration for plant fossils in promising areas and outcrops in Westphalia are a main source of additional knowledge.