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Paleobotanical Section

Stults, Debra [1], Axsmith, Brian [2].

Pterocarya sp. leaflets and fruit from the Pliocene Citronelle Formation in southwestern Alabama.

One of the significant finds of the ongoing reinvestigation of nearshore marine facies of the Citronelle Formation from sites in southwestern Alabama is the identification of Pterocarya sp. (Juglandaceae) winged fruits and leaflets. Although only six species of Pterocarya exist today and are native to Asiatic regions, the fossil record shows the taxon was once widely distributed. The conclusive fossil record of Pterocarya, as determined by its characteristic bi-winged nutlets, begins in the Eocene and includes North America. The Pterocarya record in North America continues through the Pliocene based upon leaflets and pollen from fossil sites in western North America, and pollen from the southeastern United States. The Citronelle Formation provides the first post-Miocene occurrence of Pterocarya fruits in North America. Morphological differences between the bi-winged nutlets indicate that two distinct Pterocarya species are represented in the assemblage. One specimen depicts a fruit approximately twice the size of the other and displays a finely-veined wing. The second specimen is smaller with coarsely-veined wings. Oblong leaflets with secondary veins looping just within the margin, percurrent tertiary veins, and crenate/serrate margins characteristic of Pterocarya are also present in the collection. The Citronelle Formation extends along the Gulf of Mexico Coastal Plain from southeast Texas to the Florida panhandle and its age has historically been controversial. Originally designated as Pliocene, subsequent investigators often disagreed, several favoring a Pleistocene age determination. Recent sedimentological research supports a Mid-to-Late Pliocene age (3.4 to 2.7 Ma). The discovery of Pterocarya within the Citronelle Formation lends substantial support to a Pliocene age.

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1 - University of South Alabama, Department of Marine Sciences, Life Sciences Bldg 25, Mobile, Alabama, 36688, USA
2 - University of South Alabama, Biological Sciences, Life Sciences Building #124, 307 University Blvd. North, Mobile, Alabama, 36688, USA

Citronelle Formation
winged fruit

Presentation Type: Oral Paper
Session: 26-1
Location: Salon G - Austin Grand Ballroom/Hilton
Date: Tuesday, August 16th, 2005
Time: 8:00 AM
Abstract ID:9

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