Austrocedrus from the Late Cretaceous of Antarctica and its implications for the early evolution of southern cypresses (Callitroideae, Cupressaceae).

PREMISE: The modern distribution of the southern cypresses, Callitroideae (Cupressaceae), reflects a classic Gondwanan distribution. The initial diversification of Callitroideae is estimated to have occurred during the Cretaceous, yet fossils from this period are rare, hampering our understanding of its early evolutionary history. METHODS: A permineralized cluster of callitroid seed cones has been recovered from the Late Cretaceous Santa Marta Formation on James Ross Island, Antarctica. The specimen was sectioned using the acetate peel technique. We conducted a comparative morphological and anatomical investigation of the fossil with living members of Callitroideae and tested its phylogenetic placement using Bayesian and parsimony inference methods. RESULTS: Each cone has four opposite-decussate ovuliferous complexes, a central columella, and subtending bifacially flattened shoots. This new fossil resembles living Austrocedrus in having ovuliferous complexes with a short, apically located bract tip and an abaxial row of vascular bundles. Phylogenetic reconstructions place the fossil sister to Austrocedrus chilensis, and we erect a new species, Austrocedrus vetus sp. nov. CONCLUSIONS: Austrocedrus is known by a handful of Cenozoic fossils from Australia and a single surviving taxon, A. chilensis, in the Southern Andes of Chile and Argentina. Austrocedrus vetus is the oldest evidence of the genus, extending its stratigraphic record by 40 Ma. Our findings indicate that Austrocedrus diverged by the Campanian and experienced stasis in seed cone morphology. Furthermore, this fossil is the first occurrence of Austrocedrus in Antarctica, demonstrating that the genus was an element of Antarctic forest ecosystems during the Late Cretaceous.