The Geology, Paleontology and Paleoecology of the Cerro Fortaleza Formation, Patagonia (Argentina)

The Cerro Fortaleza Formation, in southern-most Patagonia (Argentina), contains a unique flora and fauna from the Late Cretaceous (Campanian). This study is the first to assess, analyze and interpret the paleobotany of the Cerro Fortaleza Formation. Twenty-five fossil wood samples have been collected, thin-sectioned and studied. Gymnosperm morphogenera identified in this study include: Agathoxylon, Planoxylon, Taxodioxylon, Cupressinoxylon and Podocarpoxylon. This is the first record of Planoxylon, Taxodioxylon and possibly Cupressinoxylon from Argentina. The gymnosperm wood samples all possess distinct growth rings, providing strong evidence for seasonal growth regimes in the region. Additionally, two morphogenera of angiosperm wood, Hedyearyoxylon and Nothofagoxylon, have also been identified for the first time in Argentina. Of these, a new morphospecies of angiosperm wood is described. All wood morphogenera from the Cerro Fortaleza Formation, except Planoxylon, have also been described from Late Cretaceous sediments of the Antarctic Peninsula. Thus, the presence of these taxa in both regions supports Late Cretaceous plant dispersal between them. Despite sharing the same taxa, the floras from the Cerro Fortaleza Formation and the Antarctic Peninsula exhibit strikingly different relative abundances. The relative abundance of gymnosperm to angiosperm wood in the Cerro Fortaleza Formation is 75:25; whereas, coeval floras from the Antarctic Peninsula are ∼25:75. This floristic difference could be a function of regional floristic differences or a result of different depositional and/or preservational environments.;In addition to the flora, minute dinosaur teeth and bone fragments from the Cerro Fortaleza Formation are also described. This material was discovered during the preparation of the holotype of a medium-sized ornithopod, Talenkauen santacrucensis (MPM-10001). The tooth crowns are 1 mm in apicobasal height and 1.7 mm in mesiodistal width. The morphology, size and wear of the teeth and the small bone fragments suggest that the fossils were from a neonatal T. santacrucensis. This is the first record of neonatal ornithopod remains from South America. In conclusion, the work undertaken here will provide important floral and faunal data for future studies on the evolution of the Austral Basin.