Acer taurocursum

Acer taurocursum is an extinct maple species in the family Sapindaceae described from a single fossil samara found in Late Eocene 
lakebed sediments exposed in the state of Nevada, US. It is one of several extinct species placed in the living section "Rubra".
History and classification.
"Acer taurocursum" is represented by a solitary fossil specimen from the northeasternmost part of Nevada. The specimen was described by Jack A. Wolfe and Toshimasa Tanai from the "Bull Run" flora UCMP location P562, which was preserved in lacustrine sedimentation associated with extensive intermittent volcanism between . Radiometric dating of the layers of volcanic ash above and below the flora reported in 1966 indicated an age of approximately . The Bull Run flora, Copper Basin flora, and Elko flora were formed in the same time frame as a result of the activity. These three floras were possibly tied to the Salmon and Cow Creek floras of Central Idaho, and possibly with the John Day Formations Sheep rock flora in Oregon.
"Acer taurocursum" 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. elkoanum", "A. eonegundo", "A. cadaver", "A. eomediunum", and "A. axelrodi". Like "A. taurocursum", "A. cadaver" is described from fruits. "Acer axelrodi", "A. elkoanum", and "Acer eomediunum" are known from both leaves and fruits, while "A. eonegundo" is only described form foliage. Wolfe and Tanai noted that "A. taurocursum" is the oldest record of the "Acer" section "Eriocarpa". That section is now considered part of "Acer" section "Rubra".
The holotype for "Acer taurocursum" is a part specimen numbered UCMP 9089, which at the time of description was preserved in the University of California Museum of Paleontology in Berkeley, California. The specimen was studied by paleobotanists Jack A. Wolfe of the United States Geological Survey, Denver office and Toshimasa Tanai of Hokkaido University. Wolfe and Tanai published their 1987 type description for "A. taurocursum" in the "Journal of the Faculty of Science, Hokkaido University". The etymology of the chosen specific name "taurocursum" is in recognition of the type location for the species in the Bull Run flora of Nevada.
Description.
The general shape of the "A. taurocursum" nutlet is narrow and elliptic, moderately inflated, and it has a rounded tip end. The nutlet is wide and in length. The overall length of the samara is approximately and a wing width of , which is placed almost entirely behind the nutlet. The paired samaras of the species have a 20° attachment angle. The wing venation is formed by approximately twenty veins that merge along the upper margin of the wing before acutely dichotomizing and anastomosing in the wing membrane. The shape of the nutlet suggested to Wolfe and Tanai placement into "Acer" section "Eriocarpa".