Multiple Fossil Ginkgo Leaf & Winged Walnut - North Dakota

This is a spectacular multiple fossil Ginkgo leaf of the species Ginkgo adiantoides, and Juglandaceae (Winged Walnut) Fruit, from the Sentinel Butte Formation of North Dakota. It is finely detailed, and the light preservation contrasts well against the dark orangish-brown rock.

During this time in the Paleocene epoch, the Ginkgo genus was only represented by a single polymorphic species, formerly described as Ginkgo adiantoides. In 2012, the taxon Ginkgo cranei was assigned in place of Ginkgo adiantoides. This species was distributed in much of the northern regions of North America, which had a hot, humid climate at the time. Its leaves were virtually indistinguishable from modern-day Ginkgo biloba. These species of Ginkgo went extinct approximately 7 million years ago.

The Juglandaceae (walnuts, hickories, pecans) has one of the best-documented fossil records in the Northern Hemisphere. The oldest modern genus, Cyclocarya, today restricted to China, first appears in the late Paleocene (57 ma) of North Dakota, USA. Unlike walnuts and pecans that produce edible fruits dispersed by mammals, Cyclocarya fruits are small nutlets surrounded by a prominent circular wing, and are thought to be wind- or water-dispersed. Because Cyclocarya fruits are winged, they might be assumed to be wind-disperse, but their radial symmetry does not have the aerodynamic qualities typical of wind-dispersed fruits, and may have been dispersed by water.