''Acer castorrivularis'' is an extinct
maple
''Acer'' () is a genus of trees and shrubs commonly known as maples. The genus is placed in the family Sapindaceae.Stevens, P. F. (2001 onwards). Angiosperm Phylogeny Website. Version 9, June 2008 nd more or less continuously updated since http ...
species
In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...
in the family
Sapindaceae
The Sapindaceae are a family of flowering plants in the order Sapindales known as the soapberry family. It contains 138 genera and 1858 accepted species. Examples include horse chestnut, maples, ackee and lychee.
The Sapindaceae occur in tempera ...
described from a solitary
fossil
A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...
leaf
A leaf ( : leaves) is any of the principal appendages of a vascular plant stem, usually borne laterally aboveground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", while the leaves, ste ...
. The species is known from the
latest Eocene sediments exposed in the state of
Montana
Montana () is a state in the Mountain West division of the Western United States. It is bordered by Idaho to the west, North Dakota and South Dakota to the east, Wyoming to the south, and the Canadian provinces of Alberta, British Columbi ...
, USA. It is one of several extinct species placed in the living section ''
Macrantha''.
History and classification
''Acer castorrivularis'' is represented by a single fossil specimen that was recovered from a late Eocene, possibly
Chadronian
The Chadronian age within the North American Land Mammal Ages chronology is the North American faunal stage typically set from 38,000,000 to 33,900,000 years BP, a period of . It is usually considered to fall within the Eocene epoch. The Chadron ...
aged, outcrop of the Beaver Creek flora. Although it was found north of the Ruby Flora, which outcrops in southeast Montana, the similarities in overall floral composition between the Beaver Creek, Ruby, and other Montana floras are interpreted by Wolfe and Tanai to indicate that the assemblages are