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

ESCAPA I.; CATALANO SANTIAGO; ARI IGLESIAS; WILF P.

Minnesota

Congreso; Botany 2018 Thriving with Diversity; 2018

Botanical Society of America

The fossil record of Agathis has been classically restricted to Australasia and to strata noyounger than late Paleocene. Recently described fossils from the early Eocene of Patagonia(Agathis zamunerae) support a broader distribution in the past, which is reinforced herewith a new early Paleocene (early Danian, ca. 64 Ma)Agathis species. This taxon representsthe oldest definite occurrence of Agathis and perhaps the most complete preservation ofAgathis in the fossil record. The material includes leafy twigs, isolated leaves, ovuliferouscomplexes (OCs), seeds, and pollen cones with in situ Dilwynites pollen grains; it differsfrom living Agathis in having very large OCs that lack basal scallops and nearly equal-sizedseed wings. Also from Patagonia, we report leaves with Agathis affinities from the latestMaastrichtian, suggesting that the Agathis lineage survived the end-Cretaceous (K-Pg)extinction. A total evidence phylogenetic analysis was performed, including the newPaleocene species and A. zamunerae together with other fossil taxa of agathioid affinities.Eocene A. zamunerae resolved in the Agathis crown group; however, the Danian Agathisspecies occupied a stem position, showing the first evidence for early evolution in theAgathis clade and a transformation series for OC and seed features. Thus, Patagonian fossilsnow provide the first direct timeline for Agathis evolution from stem to crown. Further, thecombined presence of stem Agathis less than 2 m.y. after the K-Pg and probable Agathisleaves below the K-Pg are strong evidence for Mesozoic history in the genus. Moleculardivergence estimates have challenged the generally accepted Mesozoic age for the crowngroup of Araucariaceae, re-interpreting the fossil record of the family and suggesting thatMesozoic 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.