THE JOSE CREEK TUFF FLORA- AN EXCEPTIONAL LATE CAMPANIAN FLORA FROM SOUTH-CENTRAL NEW MEXICO

The ecological radiation of angiosperms during the Cretaceous had profound impacts on forest composition and structure, setting the stage for the development of modern vegetation. Although angiosperms attained high species richness in many environments by ~90mya, patterns of evolution in community structure and life form dominance are not well established, due in part to the small number of macrofloras that have been quantitatively sampled from a single deposit over sufficient distance to establish landscape patterns. Here, we report an exceptional late Campanian leaf macroflora (74.7 ±1 myr) preserved in a single-horizon of recrystallized volcanic ash that is exposed over a 1.2 km long transect. The flora is from the Jose Creek Member, McRae formation of south-central New Mexico, which records deposition on an alluvial plain >200km inland from the Western Interior Seaway. To reconstruct landscape patterns, we established 26 quarries along the full length of the exposure, and censused fossils at each quarry by both the number of specimens and percent cover of morphotypes using a modified line-intercept method. The deposit, which overlies a paleosol horizon indicative of well-drained conditions, contains abundant well-preserved plant macrofossils showing little to no transport, including in-situ stumps. Significant taxonomic heterogeneity exists between quarries, expected if each quarry represents locally-growing plants. To date over 140 leaf morphotypes have been recognized, based on the census of over 6,200 specimens and 30,290 2-cm line increments. Angiosperms are the most diverse (>85%) and most abundant (74.2% of specimens, 84.2% cover) plant group, followed by conifers, cycads, and ferns. Although dicots represent a significant proportion of the flora overall (46.6% specimens, and 37.5% cover), the two most abundant taxa by all metrics are a sequoioid conifer and Zingerberopsis-type monocot. Numerous reproductive structures are also found, including pollen cones, ovuliferous cones and isolated cone scales, flowers, seeds, and fruits. Here we report on the diversity and composition of the flora recovered to date, and discuss preliminary interpretations and future work.