Preliminary investigation of a diverse megafossil floral assemblage from the middle Miocene of southern Mississippi, USA

Abstract

Our understanding of Miocene floras in eastern North America is hampered by the rarity of megafossil sites. An early report from the middle Miocene Hattiesburg Formation in Mississippi included palms and Ulmus. A later report listed Taxodium, Salix, either Morus or Celtis, and monocot fragments. The floral assemblage described here was recently recovered from along the Bouie River in southern Mississippi. Ferns are represented by complete Salvinia specimens including attached sporocarps, Woodwardia, and Osmunda. Conifers are represented by branchlets of Taxodium. Angiosperms include leaves attributable to the Lauraceae. Platanus is known from leaves, stipules, and fruits. Leaflets of Sambucus are common. Cercis is recognized from leaves with palmate venation and pulvini. Leaves of Quercus sections Lobatae and Quercus have been recovered. The Juglandaceae include fruits of Juglans and two species of Carya. Morus, Populus, and Salix leaves have been recovered. Of particular biogeographical interest is a seed of Sargentodoxa, which is the first record from the southeastern coastal plain of this current Chinese endemic. Monocots include Cyperus and two types of palm, including one with armed petioles. The first vegetative fossils of Lemna from North America have been identified. Because most of the fossils are related to plants still found in the region today, the climate was probably similar to that of the modern central Gulf Coastal Plain. This flora is now one of the most extensively known in the Neogene of southeastern North America and helps to fill a major gap in our understating of Miocene plant evolution.