RECONSTRUCTING CRETACEOUS LANDSCAPES: DATA FROM WOOD ASSEMBLAGES

By the end of the Cretaceous, gymnosperms and angiosperms were the plants with secondary growth that dominated floras to a varying degree depending on location and scale. The development of secondary xylem increases the longevity of functional vascular tissue, allowing for plant structures with greater height, potentially faster growth and recovery, unique growth forms such as lianas, and adaptive response to environmental stimuli. This study examined in situ wood assemblages of gymnosperms and angiosperms from Cretaceous sites in an effort to link taxa, abundance and local distribution along the landscape. Quantitative data from the Fruitland, Kirtland, and Menefee floras of North America will be compared with available global assemblage data at similar scale. By examining specimen data in this way, we relate the co-occurrence of traits within different taxa to their local distributions, sedimentological data, spacing, and estimated tree height. The results support heterogeneity across landscapes with regard to gymnosperms and angiosperm tree representatives. Additionally, the initial spread of smaller angiosperm populations would have had an influence on microevolutionary dynamics, and likely played a significant role in the diversification of secondary xylem in angiosperms on the landscape. After the Cretaceous, greater phylogenetic variation and different environmental pressures may have overcome thresholds providing angiosperms a competitive advantage in a greater range of environments.