Agathis fossils from the Cretaceous-Paleogene boundary interval of Patagonia and the dilemma of Araucariaceae.

ESCAPA, IGNACIO; IGLESIAS, ARI; WILF, PETER; CATALANO, SANTIAGO; CARABALLO-ORTIZ, MARCOS A.; CÚNEO, N. RUBÉN

Rochester

Congreso; Botany 2018; 2018

Botanical Society of America

The fossil record of Agathis has been classically restricted to Australasia and to strata no younger than late Paleocene. Recently described fossils from the early Eocene of Patagonia (Agathis zamunerae) support a broader distribution in the past, which is reinforced here with a new early Paleocene (early Danian, ca. 64 Ma) Agathis species. This taxon represents the oldest definite occurrence of Agathis and perhaps the most complete preservation of Agathis in the fossil record. The material includes leafy twigs, isolated leaves, ovuliferous complexes (OCs), seeds, and pollen cones with in situ Dilwynites pollen grains; it differs from living Agathis in having very large OCs that lack basal scallops and nearly equal-sized seed wings. Also from Patagonia, we report leaves with Agathis affinities from the latest Maastrichtian, suggesting that the Agathis lineage survived the end-Cretaceous (K-Pg) extinction. A total evidence phylogenetic analysis was performed, including the new Paleocene species and A. zamunerae together with other fossil taxa of agathioid affinities. Eocene A. zamunerae resolved in the Agathis crown group; however, the Danian Agathis species occupied a stem position, showing the first evidence for early evolution in the Agathis clade and a transformation series for OC and seed features. Thus, Patagonian fossils now provide the first direct timeline for Agathis evolution from stem to crown. Further, the combined presence of stem Agathis less than 2 m.y. after the K-Pg and probable Agathis leaves below the K-Pg are strong evidence for Mesozoic history in the genus. Molecular divergence estimates have challenged the generally accepted Mesozoic age for the crown group of Araucariaceae, re-interpreting the fossil record of the family and suggesting that Mesozoic records of Araucaria most likely correspond to the plesiomorphic configuration for Araucariaceae. The molecular hypothesis of a Cenozoic age for the crown of Araucariaceae is here refuted based on the presence of both araucariaceous clades (i.e., Araucaria and Agathis + Wollemia) in the Mesozoic.