| Summary: | Extensive exposures of Cretaceous (144-65 Ma) strata in Argentina have yielded most of the known dinosaur taxa from the Southern Hemisphere. However, little is known about their environment. The Pari Aike Formation, in southern-most Patagonia (Argentina), yields unique dinosaurian (Talenkauen santacrucensis, Puertasaurus reuili, Orkoraptor burkeiand an unnamed Titanosaur), elasmobranch (Cretalamna appendiculata), testudine, and dipnoan fauna.The Pari Aike Formation is notable because it is the southernmost Late Cretaceous site with both floral and faunal components preserved. Throughout the Cretaceous, South America and the Antarctic Peninsula shared a continental-continental plate boundary. It is not clear whether this connection was subaerial, covered by an epeiric sea, or whether it alternated between these states. Limited terrestrial vertebrate data is available to examine the paleobiogeographic relationship between Late Cretaceous Antarctica and South America. However, fossil wood spans both of these locations and provides a potentially useful tool for understanding vertebrate paleoenvironments and paleobiogeography. To assess the usefulness of fossil wood, we collected and sectioned samples from the Pari Aike Formation (Argentina). All of the fossil wood samples have distinct growth rings, providing strong evidence for seasonal growth regimes. The relative abundance of gymnosperm wood is 73% versus 20% for angiosperms. The closest published Late Cretaceous locality is in the Antarctic Peninsula. Putatively coeval floras from the Antarctic Peninsula have distinctly different relative abundances: ~25% gymnosperm wood versus ~75% angiosperm wood. These differences suggest that these two regions, notwithstanding their close proximity, did not share a homogeneous flora. Despite the equable Late Cretaceous climate, this research points to the possibility of climatic and floral latitudinal gradients along the relatively short continental connection between South America and Antarctica. Floristic differences ...
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