Assessing Cretaceous Vegetational Change: Palynological, Mesofossil and Macrofossil Evidence from the Atlantic Coastal Plain

起重机 白垩纪中期被子植物的多样性标志着中生代陆地生态系统从蕨类植物，针叶树，苏铁和Bennettitales为主，以被子植物为主的现代生态系统的过渡。 在古植物学的记录中，这种转变比在白垩纪-第三纪边界发生的转变要深刻得多。 被子植物大化石在前阿普第阶化石植物群中稀少，但到了森诺曼期，被子植物叶多样、丰富，并经常在古植物组合中占优势。 对大型植物区系和小型植物区系（孢粉植物区系），特别是北美西部的大型植物区系和小型植物区系（孢粉植物区系）的数据的整理表明，到白垩纪末，被子植物已经达到了约40%-80%的植物区系内多样性水平，但有孢粉学和大型化石证据表明，在某些生境中，被子植物的丰度仍然低于裸子植物和蕨类植物，也许在大的地理区域。 在这一建议中，我们要求支持的angiospem多样化的模式的批判性研究，以提供更详细的洞察到该集团的崛起，生态优势，并澄清白垩纪陆地生态系统的组成的时间变化。 我们的方法将包括考虑孢粉学和宏体化石证据，但也将纳入新发现的和高度翔实的中化石组合（由小花，果实，种子，芽，叶和木材碎片），以前没有被用来建立地层范围和评估白垩纪植被变化的详细研究。 因为有一个明确的地理格局被子植物多样化（最初的辐射在低古纬度和随后的运动到高古纬度），我们专注于一系列异常保存的化石植物群在一个单一的地区-大西洋沿岸平原北美东部-在那里有可能整合数据的丰度和多样性的宏化石，中化石和花粉孢子组合。 具体而言，我们将：I）记录了从早Aptian到早Campanian的八个地点的叶、中化石和花粉-孢子组合，并根据含有可比原位孢粉形化石的中化石的亲缘关系，建立了选定的分散花粉和孢子的系统亲缘关系; ii）比较维管植物主要类群的多样性和丰度的时间变化，使用中化石数据作为在同一地点记录的大型化石和孢粉植物群模式的独立测试; iii）通过直接比较，以及通过比较分散的孢粉植物群与保存在花内的花粉和孢子，识别由不同器官系统揭示的模式中的差异，球果和孢子囊。 这些结果将被用来解释地理和地层模式的生态意义的花粉和孢子的基础上已经完成的数据库超过2,500白垩纪palnofloras从北美

9614672 Crane The mid-Cretaceous diversification of angiosperms marks the transition from Mesozoic terrestrial ecosystems dominated by ferns, conifers, cycads and Bennettitales, to more modern ecosystems dominated by angiosperms. In the paleobotanical record this transition is much more profound than that occurring at the Cretaceous-Tertiary boundary. Angiosperm macrofossils are sparse in pre-Aptian fossil floras, but by the Cenomanian angiosperm leaves are diverse, abundant and frequently dominant in paleobotanical assemblages. Compilations of data on macrofloras and microfloras (palynofloras), especially from western North America, show that angiosperms had attained within-flora diversity levels of about 40%-80% by the end of the Cretaceous, but there is both palynological and macrofossil evidence that angiosperm abundance remained subordinate to gymnosperms and ferns in some habitats, and perhaps over large geographic areas. In this proposal we request support for a critical study of the pattern of angiospem diversification to provide a more detailed insight into the group's rise to ecological dominance, and to clarify temporal changes in the composition of Cretaceous terrestrial ecosystems. Our approach will include consideration of both palynological and macrofossil evidence but will also incorporate detailed studies of newly discovered and highly informative mesofossil assemblages (composed of small flowers, fruits, seeds, shoots, and leaf and wood fragments), which have not been used previously to establish stratigraphic ranges and assess Cretaceous vegetational change. Because there is a clear geographical pattern to the angiosperm diversification (initial radiation at low paleolatitudes and subsequent movement into high paleolatitudes), we focus on a sequence of exceptionally-preserved fossil floras in a single area - the Atlantic Coastal Plain of eastern North America - where it is possible to integrate data on the abundance and diversity of macrofossils, mesofossils and po llen-spore assemblages. Specifically we will: I) document the leaf, mesofossil and pollen-spore assemblages from eight localities ranging in age from Early Aptian to Early Campanian and establish the systematic affinities of selected dispersed pollen and spores based on the affinities of the mesofossils containing comparable in situ palynomorphs; ii) compare temporal changes in the diversity and abundance of major groups of vascular plants, using data from mesofossils as an independent test of patterns documented at the same sites by macrofossils and palynofloras; iii) identify discrepancies in the patterns revealed by different organ systems, both through direct comparison, and through comparison of dispersed palynofloras with pollen and spores preserved within flowers, cones and sporangia. These results will be used to interpret the ecological significance of geographic and stratigraphic patterns in pollen and spores based on an already completed database of more than 2,500 Cretaceous palnofloras from North America