EXTINCT TRANSITIONAL FAGACEAE FROM THE OLIGOCENE AND THEIR PHYLOGENETIC IMPLICATIONS

Fruits, catkins, and associated leaves of at least two extinct trigonobalanoid taxa have been discovered at an Oligocene fossil plant locality rich in fagaceous remains. These fossils exhibit a mosaic of fruit and pollen characters found in the two extant subfamilies Castaneoideae and Fagoideae of Fagaceae. Comparison with cladograms based on modern taxa suggests that these extinct taxa were similar to the ancestors of subfamily Fagoideae and may have been intermediate between Fagus and the modern trigonobalanoid genera. Pollen types isolated from the fossil staminate catkins provide unique character states that are transitional between modern pollen types in Fagaceae and are important in understanding the evolution of exine micromorphology within the family. This analysis provides a striking example of the use of character data from fossils to determine character‐state adjacency prior to polarization of characters using outgroup comparison. Because of the mosaic nature of their character complexes, these fossils support monophyly in both the family Fagaceae and the subfamily Fagoideae. In addition, the occurrence of trigonobalanoid fossils in the Oligocene of North America has interesting biogeographic implications and provides insights into the nature of North American Fagaceae during the Tertiary.