MANCHESTER, STEVEN R. Paleobotany Laboratory, Florida Museum of Natural History, Gainesville FL 32611-7800. - Leaves and fruits of Aesculus antiquorum (Newberry) Iljinskaya (Sapindales) from the Paleocene of North America.
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Aesculus has been reported previously from Tertiary deposits of
the Northern Hemisphere based on isolated leaflet impressions, but
corroborative data from complete, palmately compound leaves and from
reproductive organs has been scarce. It is now possible to confirm
this genus in the Paleocene of North America based on combined
evidence from complete leaves, fruits and seeds. Fossil leaflets from
the Paleocene of North Dakota, Montana and Wyoming that were
previously assigned to the Juglandaceae as Carya antiquorum
Newberry were transferred to Aesculus by Iljinskaya in 1968
based on her assessment of fossil leaflets described and illustrated
in the literature. However, this transfer was largely overlooked by
North American workers. Recently discovered complete, palmately
compound leaves and associated trivalved fruits from the Fort Union
Formation of North Dakota and Wyoming confirm that the fossils
represent Aesculus. Each leaf has a long petiole with an
expanded base and bears three to five obovate, sessile leaflets with
finely serrate margins. Fruits are preserved as three-dimensional
impressions in siltstone in association with these leaves at three
localities: Little Bitter Creek and Rock Springs, Wyoming, and
Trenton Hill, North Dakota. The fruits are trivalved, globular
loculicidal capsules with spiny ornamentation. Globular seeds
sometimes remain attached to the valves. Silicified seeds found with
the leaves at Almont, North Dakota, correspond in seedcoat anatomy to
extant Aesculus. The spiny ornamentation on the fruit valves
matches that of A. glabra (eastern North America) and A.
hippocastanum (eastern Europe); all other extant species are
smooth or verrucate. The fossil species differs from extant Asian
species by its spiny fruits, and its sessile, somewhat asymmetrical
leaflets. These fossils indicate that the extant genus was already
established by the late Paleocene in North America, complementing
foliage remains from the Paleogene of Spitsbergen and Kamchatka and
predating the Oligocene occurrences from mainland Europe.
Key words: Aesculus, fruits, leaves, Paleobotany, Paleocene, Tertiary