Upchurch, Garland , Wolfe, Jack .
Re-examination of foliage of Nelumbonaceae from the Cretaceous and Early Tertiary of North America.
Nelumbonaceae is a family derived from the mid-Cretaceous radiation of eudicots. Nelumbo "the sole extant genus" is highly specialized in its vegetative and reproductive morphology. Leaves of extant Nelumbo are easily recognized by their peltate orbicular shape, the presence of a central disc, thick primary venation with radial organization, an unbranched midvein that produces no secondary veins, 11 or more pairs of primary veins that bifurcate and form loops within the margin, percurrent tertiary venation, and hexagonal areolation. Re-examination of the North American leaf record indicates that the Nelumbonaceous stem lineage appears during the Early Cretaceous but that forms fully comparable to extant Nelumbo do not appear until the Tertiary. The oldest well-documented occurrence of Nelumbonaceae is Nelumbites extenuinervis, an Early Cretaceous (middle-late Albian) species that is characterized by orbicular peltate leaves with radially organized primary venation and floral receptacles with embedded fruits. Many features of leaf architecture in N. extenuinervis are generalized relative to those of extant Nelumbo, including thin primary venation, a midvein that gives rise to brochidodromous secondary veins, 3-5 pairs of lateral primary veins, reticulate tertiary venation, and areoles of variable shape. Published leaves of latest Cretaceous and earliest Tertiary age, when assignable to Nelumbonaceae, are best referred to Nelumbago. Nelumbago has additional specializations that include thick primary veins, a midvein that does not give rise to secondary veins, and at least 11 pairs of primary veins, but retains generalized features such as reticulate tertiary venation and areoles of variable shape. Leaves with all the specializations of extant Nelumbo, such as N. aureavallis, have their first well-documented occurrence during the late Paleocene to early Eocene. This implies that the Nelumbo crown group may be no older than Tertiary in age and that its specializations were accumulated gradually during the Late Cretaceous and Early Tertiary.
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1 - Texas State University, Department of Biology, 601 University Drive, San Marcos, Texas, 78666, USA
2 - University of Arizona, Department of Geosciences, Tucson, Arizona, 85721, USA
Presentation Type: Oral Paper
Date: Monday, August 15th, 2005
Time: 3:30 PM