The fossil genus Aextoxicoxylon (Magnoliopsida) in the Upper Cretaceous Puntudo Chico Formation, Chubut Province, Argentina

A new fossil dicot wood recovered from the Upper Cretaceous Puntudo Chico Formation is here identified as a representative of the fossil genus Aextoxicoxylon. Differences with the type species support the recognition of a new species, Aextoxicoxylon kawasianus sp. nov. This new taxon is characterized by having indistinct growth rings, solitary vessels, diffuse porosity, perforation plates scalariform with high number of bars, and heterocellular rays. All these features are typical of primitive woods according to Baileyan trends. Furthermore, anatomy of the wood, and the presence of fungal hyphae in vessels, suggests non-seasonal and probably warm and humid climate, which agrees with previous proposals for the Puntudo Chico Formation and other units of similar ages. Aextoxicoxylon is a new element previously not recognized in the Late Cretaceous to Danian floristic assemblages that seem to have been linked to the Kawas Sea, a shallow sea that developed in Patagonia at the end of the Cretaceous.