CONICET | Buscador de Institutos y Recursos Humanos

Early Paleocene macrofloras from the Southern Hemisphere are virtually unknown, despite their enormous potential significance forunderstanding plant evolution, biogeography, and global variation in recovery from the end-Cretaceous extinction. We here report 51angiosperm leaf morphotypes from 3,522 specimens recovered from three distinct, early to late Danian time intervals (geomagneticpolarity chrons C29n, C28n, and C27n, respectively) of the Salamanca and Peñas Coloradas formations, San Jorge Basin, centralPatagonia, Argentina. These assemblages were noted previously but with minimal descriptions and inadequate age constraints; theynow comprise the first stratigraphically controlled and quantitatively collected sequence of early Paleocene macrofloras from theSouthern Hemisphere. Preliminary botanical affinities of the morphotypes include Nothofagus, Fabaceae, and Menispermaceae, whichare potentially the oldest macrofloral records of these lineages. Other families likely to be present include Arecaceae, Araceae,Cunoniaceae, Lauraceae, ?Malvaceae, Rosaceae, Sapindaceae, and Urticaceae (angiosperm reproductive organs from these sites,as well as ferns, araucarian and podocarpaceous conifers, insect body fossils and leaf-feeding traces, and feathers are under separateinvestigation). A striking result of this study is the general lack of change in floral composition or dominance through the Danian, eventhough the depositional environments shift from estuarine to continental. Like nearly all North American floras of this time, those fromthe San Jorge Basin of Patagonia appear to represent a homogenous, generalist, persistent vegetation type. However, theconsiderably higher richness of Danian floras from Patagonia, along with much other evidence from Southern Hemisphere continentalenvironments, supports the idea of geographic variation in biotic response related to distance from the Chicxulub impact site and otherpotential factors.