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

白垩纪中期被子植物的多样化标志着中生代以蕨类、针叶树、苏铁和贝纳特属植物为主的陆地生态系统向以被子植物为主的现代生态系统的转变。在古植物学记录中，这种转变比发生在白垩纪-第三纪界线上的转变要深刻得多。被子植物的大型化石在前阿普提亚化石区系中较少，而在塞诺曼尼亚被子植物的叶系中，被子植物的叶系丰富多样，在古植物组合中占主导地位。大植物区系和微植物区系（孢粉区系）的数据汇编，特别是来自北美西部的数据显示，到白垩纪末期，被子植物的区系多样性水平已达到40%-80%左右，但孢粉学和大化石证据表明，在某些栖息地，可能在较大的地理区域，被子植物的丰度仍然低于裸子植物和蕨类植物。在这一提议中，我们请求支持对被子植物多样化模式的批判性研究，以提供更详细的见解，以了解该群体如何崛起为生态优势，并澄清白垩纪陆地生态系统组成的时间变化。我们的方法将包括对孢粉学和宏观化石证据的考虑，但也将纳入对新发现和信息丰富的中化石组合（由小花、果实、种子、芽、叶和木碎片组成）的详细研究，这些中化石组合以前没有被用于建立地层范围和评估白垩纪植被变化。由于被子植物多样化具有明确的地理格局（在低古纬度开始辐射，随后向高古纬度移动），因此我们将重点放在北美东部大西洋沿岸平原这一单一地区保存完好的化石区系序列上，在那里可以整合大化石、中化石和花粉孢子组合的丰度和多样性数据。具体而言，我们将：1)记录从早阿普tian到早坎帕尼亚的8个地点的叶子、中化石和花粉-孢子组合，并根据含有可比原位孢型的中化石的亲缘关系建立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大型化石和孢粉植物在同一地点记录的模式的独立测试；Iii)通过直接比较，以及通过将分散的孢粉植物与保存在花、球果和孢子囊内的花粉和孢子进行比较，确定不同器官系统所揭示的模式的差异。这些结果将用于解释花粉和孢子的地理和地层模式的生态意义，这些模式基于一个已经完成的2500多个白垩纪北美palnoflora数据库

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