Oral Paper

         Paleobotany

A Nothofagus-like fruit from the Campanian of Western North America

Presenting Author
Kate Morrison
Description
The genus Nothofagus Blume (southern beech; Nothofagaceae, Fagales) has a substantial fossil record across the Southern Hemisphere. Its first appearance in the fossil record is represented by pollen grains preserved in late Campanian to Maastrictian deposits from Antarctica. Due to its extensive fossil record and southern distribution, Nothofagus remains an important group for understanding the evolution and biogeographical history of Gondwanan floras.  While the reported fossil record of Nothofagus is restricted to Gondwanan landmasses, there are a number of Nothofagus-like fossils from North America. These fossils have been important for understanding the early evolution of Fagales, mainly the phylogenetic and morphological divergence between Nothofagaceae and all other Faglaes. Here we present a fagalean fossil fruit with similarities to Nothofagus. The specimen is a single trimerous fruit recovered from EV Henry Point, Sucia Island State Park, Washington. Deposits at this locality belong to the Cedar District Fm, which is early Campanian (~80 Ma) in age. Serial acetate peels were made, followed by light microscopy and a 3D reconstruction, allowing the characterization of morphological and anatomical characteristics. The fruit is about 8.8 mm in cross sectional length and is missing the basal portion. It has three longitudinally elongated wings and three glabrous locules separated by thin septa that are ruptured in some areas. The pericarp is differentiated into epicarp, mesocarp, and endocarp. The epicarp includes thick-walled cells and idioblasts. The mesocarp comprises fibers and parenchyma while the endocarp comprises small, thick-walled sclereids. The mesocarp and epicarp extend to form the fruit wings, in which case it becomes parenchymatous with scattered sclereids. The wings are up to 3.9 mm in length. There are two ovules per locule, with axile placentation attached to an apical placental column. A parenchymatous tissue fills the locule cavity below the level of the ovules. There is a single whorl of three persistent tepals at the apex of the fruit. This combination of characters is highly diagnostic of Fagales, especially Nothofagaceae. A number of Nothofagus-like fruit containing cupules and isolated fruits have been previously described from the Late Cretaceous of North America; however, these fossils differ from the extant genus by key characters such as the number of tepal whorls and tomentose locules, which has precluded them from being assigned to Nothofagaceae. Conversely, the fossil described here has fruit characters diagnostic of Nothofagus, but important cupule characters are missing. Thus, we refrain from assigning the fossil to the genus at this time. Nonetheless, this fossil adds to the diversity of Nothofagus-like fossils from the Cretaceous of North America and we assign it to Nothofagaceae. This systematic assignment is further supported by the presence of permineralized nothofagaceous fruits with similar anatomy from coeval deposits in Antarctica. This new occurrence of a nothofagaceous fruit from the Late Cretaceous of North America suggests a wider distribution of the family than previously thought and supports a hypothesized biotic exchange between North America and Gondwana that occurred during this time.