''Acer eonegundo'' 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 single partial

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

Eocene The Eocene ( ) Epoch is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene' ...

sediments exposed in the US state of

Nevada Nevada ( ; ) is a U.S. state, state in the Western United States, Western region of the United States. It is bordered by Oregon to the northwest, Idaho to the northeast, California to the west, Arizona to the southeast, and Utah to the east. N ...

. It is placed into the living ''Acer'' section '' Negundo''.

History and classification

''A. eonegundo'' is represented by a solitary fossil specimen from the northeastern part of Nevada. The specimen was recovered from an outcrop of the "Bull Run" flora, University of California Museum of Paleontology location P562, which preserves lacustrine sedimentation associated with extensive intermittent volcanism between .

Radiometric dating Radiometric dating, radioactive dating or radioisotope dating is a technique which is used to date materials such as rocks or carbon, in which trace radioactive impurities were selectively incorporated when they were formed. The method compares t ...

of volcanic ash layers above and below the flora reported in 1966 indicated an age of approximately . The Bull Run, Copper Basin, and Elko floras were formed during the same time frame as a result of the volcanic activity. The three floras are possibly tied to the Salmon and Cow Creek floras of Central Idaho, and also possibly with the John Day Formations Sheep rock flora in Oregon. The

holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of several ...

for ''A. eonegundo'' is a part specimen numbered UCMP 9043, which at the time of description was preserved in the University of California Museum of Paleontology in

Berkeley, California Berkeley ( ) is a city on the eastern shore of San Francisco Bay in northern Alameda County, California, United States. It is named after the 18th-century Irish bishop and philosopher George Berkeley. It borders the cities of Oakland and Emer ...

. The specimen was studied by paleobotanists

Jack A. Wolfe Jack Albert Wolfe (1936–2005) was a United States Geological Survey paleobotanist and paleoclimatologist best known for his studies of Tertiary climate in western North America through analysis of fossil A fossil (from Classical Latin ...

of the United States Geological Survey, Denver office and Toshimasa Tanai of Hokkaido University, with Wolfe and Tanai publishing their 1987

type description A species description is a formal description of a newly discovered species, usually in the form of a scientific paper. Its purpose is to give a clear description of a new species of organism and explain how it differs from species that have be ...

for ''A. taurocursum'' in the ''Journal of the Faculty of Science, Hokkaido University''. The

etymology Etymology ()The New Oxford Dictionary of English (1998) – p. 633 "Etymology /ˌɛtɪˈmɒlədʒi/ the study of the class in words and the way their meanings have changed throughout time". is the study of the history of the Phonological chan ...

of the chosen

specific name Specific name may refer to: * in Database management systems, a system-assigned name that is unique within a particular database In taxonomy, either of these two meanings, each with its own set of rules: * Specific name (botany), the two-part (bino ...

''eonegundo'' is a combination of ''negundo'' for ''Acer'' section ''Negundo'' and "eo" for Eocene, alluding to the species being an Eocene member of the section. ''A. eonegundo'' is one of six ''Acer'' species to be described by Wolfe and Tanai in 1987 from the "Bull Run" flora, with the others being '' A. axelrodi'', '' A. cadaver'', '' A. elkoanum'', '' A. eomediunum'', and '' A. taurocursum''. While ''A. eonegundo'' is only described form foliage, ''A. taurocursum'' and ''A. cadaver'' are described only from fruits. ''A. axelrodi'', ''A. elkoanum'', and ''A. eomediunum'' are known from both leaves and fruits. When described, Wolfe and Tanai noted ''A. eonegundo'' to be the oldest leaf fossil record for the ''A.'' sect. ''Negundo'', with relationships between ''A. eonegundo'' the younger members of the section unclear.

Description

''A. eonegundo'' has

compound leaves 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 ...

divided into at least three leaflets, with the leaflets

pinnate Pinnation (also called pennation) is the arrangement of feather-like or multi-divided features arising from both sides of a common axis. Pinnation occurs in biological morphology, in crystals, such as some forms of ice or metal crystals, and in ...

ly veined and ranging up to in length. The leaflets have small petiolules and asymmetric bases flaring out on the basal side while remaining narrow on the apical side. Each lateral leaflet has 7 secondary veins that fork near the leaf margin with the inner branch curving upwards to join the next secondary vein up, while the outer fork extends to the leaf margin. The outer forks brace the sinuses between the teeth on the blade margins. Overall the teeth of the leaflets compound, each of the large teeth having 1 to 2 smaller teeth on the basal side. The leaves have tertiary veins that form acute angle-right angle structuring with the veins spaced apart. The quaternary veins form a network of areoles that are irregular polygons.

References

{{Taxonbar, from=Q29641583 eonegundo Plants described in 1987 Fossil taxa described in 1987 Eocene plants Flora of North America Extinct flora of North America

† A dagger, obelisk, or obelus is a typographical mark that usually indicates a footnote if an asterisk has already been used. The symbol is also used to indicate death (of people) or extinction (of species). It is one of the modern descendan ...