Fossil Ginkgo Leaf with Winged Walnut Fruit - North Dakota

This is a beautiful fossil Gingko leaf (Ginkgo adiantoides) that's associated with a winged walnut fruit (Cyclocarya brownii) from the Sentinel Butte Formation of South Dakota. It is finely detailed and the light preservation contrasts well against the dark orangish-brown rock.

During this time on the Paleocene epoch the Ginkgo genus was only represented by a single polymorphic species, Ginkgo adiantoides. This species was distributed in much of the Northern regions of North America which had a hot, humid climate. It's leaves were virtually indistinguishable from modern-day Ginkgo biloba. The species Ginkgo adiantoides 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.

A paper describing these fruits in depth is linked below.

Cyclocarya brownii from the Paleocene of North Dakota, USA
Ginkgo adiantoides & Cyclocarya brownii (Fruit)
Morton County, North Dakota
Sentinel Butte Formation
1.2" wide leaf on 5 x 3.7" rock
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