Paleobotany is the study of fossil plants that are preserved in stratified sedimentary rocks. They are impressed, incrusted with mineral films or the organic matter is compressed between the rock layers providing the durable tissues for microscopic analysis. Occasionally the tissues are replaced by mineral substances retaining their cellular structure. Small objects, like spores and pollen grains are immersed in the rock matrix and can be extracted with special techniques. Fine morphological details come to light and developmental processes can be inferred from a well-preserved and properly studied material. The paleobotanical materials contain a wealth of information on the history of vegetation and evolution of plants, as well as on climates, environmental change, habitats of ancient animals and humans, plant – animal interactions, and the whole ecosystem development through time. Fossil plant localities are found in the course of geological reconnaissance and mapping of sedimentary basins. All data concerning the rock types, their depositional environments and secondary alterations are collected as the taphonomic information related to paleoecological reconstructions. The laboratory techniques include cuticle preparations, peeling and transfer from rock to transparent films, sectioning, and spore - pollen preparation for the high resolution light microscopy and the scanning/transmission electron microscopy, as well as photographic documentation of the results. A special method developed in the laboratory allows extraction and processing of structurally preserved plant remains from the guts of fossil insects (Link 1).
Fossil plant cites and cooperation: Fossil plant cites in Israel are mainly located in the erosional craters (makhteshim) of the central Negev Desert and on the western slope of the Arava Rift Valley. The plant-bearing Jurassic and Cretaceous deposits are exposed form under the cover of marine limestones (Link 2). Summarily, they characterize the most important period in the history of land flora: the advent and early evolution of flowering plants. The field studies are carried on in cooperation with the Geological Survey of Israel and the Technical University of Berlin. The depository also contains collections from Jordan, Lebanon and Libya. The comparative material for international stratigraphic correlation, continental paleophytogeography and paleoclimatic reconstructions comes from Russia, Kazakhstan and Mongolia and is studied in collaboration with Paleontological Institute, Russian Academy of Sciences and Paleontological Center, Mongolian Academy of Sciences (Link 3).
Research problems, approaches and achievements The regional paleofloristic studies, such as the systematic description and analysis of the Late Cretaceous (Turonian) flora of Arava, Israel (Link 4) and the Early Cretaceous flora of the Negev (in preparation, Link 5 A, B) constitute the major part of the published output. However, the results are also relevant to the major problems of plant evolution and the macroevolution – ecosystem evolution theory, such as: 1. Plant phylogeny and the origins of higher taxa; 2. Ontogenetic – phylogenetic parallelism and recapitulation; 3. Macromorphological systemic transformations; 4. Syngenesis (biotic community evolution) and evolutionary novelties; 5. Biotic interaction: evolution of feeding behavior, pollinivory, and leaf parasitism in the plant – arthropod interactions; 6. Mass extinctions, major innovations and global change.
1. Phylogenetic reconstructions are based on “fossil links”, showing intermediate character states or mosaic combinations of archaic and innovative traits, as well as on the tendencies of morphological transformation traceable through time from the ancestral to descendent forms. This approach is seen as an alternative to the formal cladistic analysis.. The origins of higher taxa, or new structural types, is considered to be a complex evolutionary event, including (a) the “prophetic” stage, during which the key characters of a new group appear in a number of parallel lineages and (b) the “realization” stage, at which the key characters are integrated into a new functional system (File 3) followed by ecological expansion and explosive radiation of the group (Link 6).
2. Certain results of the recent “evo - devo” studies are applied to interpretation of morphological traits in extant and fossil plants, such as a relict genus Cercidiphyllum for which a neotenous ancestral form is postulated and confirmed by paleobotanical data (Link 7 A-C). Stomatal structures in extant and fossil leaves are involved in the analysis. (Link 8).
3. Macromorphological transformations are interpreted as associated epigenetic and regulatory macromutation events, affecting early developmental stages and giving rise to pedomorphous structures that are conserved in the ontogeny as recapitulations (Link 7; Link 8).
4. The macromutational origins of new morphologies are correlated with the major ecogenetic events – the appearance of a new type plant communities. This is illustrated by the appearance of weedy angiosperms in the new type mid-Cretaceous communities (Link 7; Link 9) , as well as by explosive evolution of angiosperms simultaneously with the appearance of angiosperm mangroves in the mid-Cretaceous in the Turonian of Arava, Israel (Link 10 A-D).
5. The plant – arthropod interaction in the Turonian of Arava, Israel is the first regional survey with taxonomic descriptions based on a new morphological classification of plant damages caused by a rich folivorous – parasitic arthropod community (Link 11). One of the evolutionary meaningful results pertains to direct correlation between the gall advancement level and the level of biological complexity (in particular, the occurrence of gall/mine predation and environmental stability (Link 12).
6. The new data and analysis of floristic evolution over the chronostratigraphic boundaries marked by mass extinctions (the Permian/Triassic and Cretaceous/Paleogene) (Link 13) show that, at the ecosystem level, such events are related to the environmentally induced changes in the ratios of biomass to dead mass production, non-selective elimination, and the concomitant switches from coherent to non-coherent evolution, the main features of the latter being prolific reproduction (the Niobe reproductive strategy) and accelerate development at the roots of macroevolutionary novelties (Link 14; Link 15).