Manchester, Steven , Wing, Scott .
Hernandiaceae in the Early Eocene of North America.
The Lauralean family Hernandiaceae, with five extant genera and about 60 species, is widely distributed in the tropics today. Until recently the family was virtually unknown from the fossil record, despite the extensive paleobotanical record of the related family Lauraceae, which was widespread in the Late Cretaceous and Tertiary. We have identified fruits and leaves of Hernandiaceae from the Early Eocene of Wyoming. The fruits are elongate-ellipsoidal with conspicuous paired epigynous wings. The wings are elongate-oblanceolate, entire-margined, with rounded apices, and have longitudinally oriented, subparallel, dichotomizing and anastomosing venation without clear distinction into primary and secondary veins. The wing tissue is covered with evenly spaced circular amber dots interpreted to represent solidified contents of ethereal oil cells. Associated leaves have long petioles and broad, asymmetrical laminae that vary from unlobed to bilobed and trilobed (occasionally to 6-lobed). Major venation is suprabasal palinactinodromous with three to five primaries; the three middle primaries extend to the tips of the lobes, and the outer primaries run inside the margin and merge with a series of weak loops formed by secondary veins. Unlobed and bilobed (mitten-shaped) laminae have similar venation except for the reduced thickness of primaries. Secondary veins are eucamptodromous and widely and irregularly spaced. Tertiary veins are widely spaced and reticulate to weakly percurrent. This suite of characters supports identification of these fruits and leaves to Gyrocarpus - a pantropical genus no longer occurring in mid-latitudes. These fossils first occur during the Paleocene-Eocene Thermal Maximum in the basal part of the Willwood Formation in the Bighorn Basin (~55.8 MA) and are also known from the Fossil Butte(~52 MA) and Parachute Creek (~48 MA) Members of the Green River Formation, in southwestern Wyoming, northwestern Colorado and northeastern Utah. These records complement the recently recognized occurrences of Illigera eocenica based on distinctive cat-eye shaped samaras from the Early and Middle Eocene of Colorado, Utah, Wyoming and Oregon. This indicates that both major clades of Hernandiaceae inhabited mid-latitudes during the warmest part of the Eocene.The biogeographic sources and pathways of dispersal remain uncertain because no fossils from other continents have been verified and the phylogenetic position relative to extant species is uncertain. The Eocene North American population of Gyrocarpus may have played a role in geographic dispersal and/or vicariance between the New and Old World tropics.
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1 - University Of Florida, Florida Museum Of Natural History, PO BOX 117800, Gainesville, FL, 32611, USA
2 - Smithsonian Institution, Dept. Of Paleobiology NHB 121, PO Box 37012, WASHINGTON, DC, 20013-7012, USA
Presentation Type: Oral Paper:Papers for Sections
Location: Delaware B/Hyatt
Date: Wednesday, July 11th, 2012
Time: 4:15 PM