DISCUSSION

Nearly all the identified plant taxa in the Red Hot flora represent groups with predominant or exclusive distribution in tropical to subtropical biomes (e.g., Gentry 1993; Heywood 1993), indicating warm temperatures at this time in the Gulf Coast. A majority of identifiable taxa also have close relatives from well constrained early Eocene localities in the western USA, showing that these groups were widespread in North America shortly after (and possibly during) the PETM. Lygodium kaulfussi appears just above and possibly within the PETM in Wyoming (Wing 1998; Wing et al. 2005); the modern genus is known for its diverse reproductive strategies, including selfing, that appear to expedite long-distance dispersal and colonization (Lott et al. 2003). Lauraceae are known continuously from the late Paleocene and early Eocene of Wyoming (Wing 1998; Wilf 2000). Myrtaceous fruits (Paleomyrtinaea Pigg et al. 1993) are known from the late Paleocene of North Dakota and southern Wyoming and from the Eocene of British Columbia (Crane et al. 1990; Pigg et al. 1993; Wilf 2000); myrtaceous leaves (Syzygioides americana [Lesquereux] Manchester et al. 1998) appear in the Wyoming fossil record about 2 m.y. after the PETM (Manchester et al. 1998; Wing 1998; Wilf 2000) and extend to the middle Eocene Green River floras (MacGinitie 1969; Manchester et al. 1998). Legumes, not similar to those at the Red Hot leaf flora, are found in the early Eocene of Wyoming including the PETM (Wing 1998; Wilf 2000; Wing et al. 2005). In the Bighorn Basin, Platycarya pollen occurs in the lowermost Eocene, and its foliage occurs about 2 m.y. later (Wing 1984, 1998; Wilf 2000). The Platycarya specimen from the Red Hot leaf flora (Figure 5) is the first macrofossil of the genus from eastern North America. Rhus is well represented in late early Eocene floras of the western USA (e.g., Wing 1998; Wolfe and Wehr 1987; Wilf 2000), and the genus is probably present in Wyoming during the PETM (Wing and Lovelock 2007). To our knowledge, those here presented are the first reliable fossil leaves of Ochnaceae, a diverse pantropical group concentrated in today's Neotropics with a possible fruit record from the late Paleocene of North Dakota (Pigg and DeVore 2005).