INTRODUCTION

Numerous Eocene macrofloras from the North American Gulf Coast, found in strata known historically as the Wilcox and Claiborne Groups, have produced a classic suite of botanical discoveries (e.g., Berry 1914, 1916, 1923, 1924, 1930, 1937; Dilcher 1963, 1969, 1973a, 1973b; Dilcher and McQuade 1967; Dilcher and Mehrotra 1969; Dilcher and Dolph 1970; Dilcher et al. 1976; Dilcher and Daghlian 1977; Crepet et al. 1974, 1975; Crepet and Dilcher 1977; Roth and Dilcher 1979; Jones and Dilcher 1980; Kovach and Dilcher 1984; Dilcher and Manchester 1986, 1988; Grote and Dilcher 1989, 1992; Herendeen and Dilcher 1990a, 1990b, 1990c; Call and Dilcher 1992, 1995; Herendeen 1992; Dilcher and Lott 2005). These studies have provided fundamental information about the origins and early diversity of living and extinct plant groups, as well as Eocene paleoclimates of the Gulf Coast. However, the floras mostly come from stratigraphically isolated and poorly dated clay pits (e.g., Dilcher 1973a; Dilcher and Lott 2005), and thus the considerable record cannot be well placed into a chronological framework. Little progress has been made since Berry's investigations to correlate megafloral deposits, although Wolfe and Dilcher (2000) made preliminary efforts in Texas. The Claiborne floras, the target of nearly all systematic investigations, are now considered middle Eocene (Dilcher 1973a; Dilcher and Lott 2005).

A highly fossiliferous Wilcox section from Meridian, Mississippi, known as the Red Hot Truck Stop locality (Figure 1) after a former business nearby, is unusually well constrained stratigraphically. The Red Hot Truck Stop section contains the latest Paleocene and earliest Eocene upper Tuscahoma Formation and the early Eocene Bashi and Hatchetigbee Formations, dated locally from mammals, pollen, dinoflagellates, and sequence stratigraphy, and from calcareous nannoplankton and foraminifera in correlative deposits elsewhere (Siesser 1983; Beard and Tabrum 1991; Ingram 1991; Gibson and Bybell 1994; Frederiksen 1998; Beard and Dawson 2001; Harrington 2003a). The Red Hot Truck Stop locality is particularly notable for being the only site east of the Rocky Mountain region that contains an extensive and diverse suite of Wasatchian mammals. The Red Hot local fauna, first discovered by G.R. Case in 1979 (see Beard and Dawson 2001) now includes 11 mammalian orders and more than 24 species to date, primarily from the uppermost Tuscahoma Formation (Beard and Tabrum 1991; Beard and Dawson 2001; Dawson and Beard 2007). Among these are marsupials, primates, rodents, condylarths, perissodactyls, artiodactyls, pantolestids, pantodonts, and carnivores (Beard and Dawson 2001; Dawson and Beard 2007). The Tuscahoma Formation at the Red Hot Truck Stop locality also contains more than 30 fossil species of bony and cartilaginous fish as well as remains of snakes, birds, lizards, and crocodilians (Case 1986, 1994a, 1994b; Holman et al. 1991; Ingram 1991; Holman and Case 1992; Beard and Dawson 2001), and the Bashi Formation contains mammals, bivalves, gastropods, and trace fossils (Beard and Tabrum 1991; Ingram 1991).

Call et al. (1993) described a macrofloral assemblage from the Bashi Formation at the Red Hot Truck Stop locality with degraded wood, fern rhizomes (also found in the uppermost Tuscahoma), and angiosperm fruits permineralized in pyrite. These authors interpreted the fruits of Wetherellia (an extinct genus of unknown affinity) as water-dispersed from mangrove or other warm coastal habitats. Harrington (2003a; see also Harrington and Kemp 2001; Harrington 2001, 2003b; Harrington and Jaramillo 2007; Harrington et al. 2004) found 113 palynomorphs from the Tuscahoma and Bashi formations at the Red Hot Truck Stop locality, some representing characteristically thermophilic families such as Annonaceae, Arecaceae, Burseraceae, Fabaceae, and Sapindaceae. Ingram (1991) first noted the presence of compression/impression fossil leaves in the lower Bashi Formation, which are described here for the first time from a new collection. Although the here-designated Red Hot leaf flora is generally not well-preserved, it holds importance as the only Gulf Coast macroflora to date that can be placed confidently in the very early Eocene, less than ~1.6 m.y. after, or possibly within, the Paleocene-Eocene Thermal Maximum (PETM), as discussed below.

The onset of the PETM at 55.8 Ma coincides with the Paleocene-Eocene boundary and the base of the Wasatchian North American land-mammal age (Gradstein et al., 2004). The PETM and the broader late Paleocene-early Eocene time interval are well-known for both rapid and long-term warming events that affected organisms in marine and terrestrial environments (e.g., Gingerich 1989, 2006; Kennett and Stott 1991; Koch et al. 1992; Wing 1998; Wilf 2000; Zachos et al. 2001; Gibbs et al. 2006). However, previous studies have not yielded much stratigraphically controlled information about early Eocene vegetation in subtropical latitudes. The early Eocene age of the Red Hot leaf flora allows comparisons to the more heavily studied, coeval Western Interior floras. Most of the well-dated early and middle Eocene floras from North America were collected at middle to high latitudes in the Rocky Mountain region and the Pacific Northwest (e.g., Wing 1987; Wolfe and Wehr 1987; Manchester 1994; Wolfe et al. 1998). The highest temporal resolution for early Eocene floras comes from the densely sampled Bighorn and greater Green River basins of northwestern and southwestern Wyoming, respectively (Wing 1998; Wilf 2000; Wing et al. 2000, 2005; Wing and Harrington 2001). The Bighorn Basin holds the only well-constrained PETM macrofloras (Wing et al. 2005; Wing and Lovelock 2007).

In this paper, we describe 18 leaf morphotypes and two dispersed cuticle morphotypes from the Red Hot leaf flora, provide identifications when possible, and make comparisons to floras of equivalent age from the better understood Rocky Mountain region.