INTRODUCTION

The lowland neotropical flora of La Selva Biological Station in Costa Rica (10°26'N, 84°00'W) is predominately that of an undisturbed tropical wet forest. The station also includes some secondary forest, along with areas of swamp, riparian, disturbed, and managed vegetation (McDade et al. 1994). Research at La Selva has included numerous studies of the extant flora (Hartshorn and Hammel 1994; Wilbur 1994), along with some paleoecological research focused on pollen and charcoal evidence of Late Quaternary vegetation and fire history (Horn and Sanford 1992; Kennedy and Horn 1997, 2008; Horn and Kennedy 2001; Titiz and Sanford 2007). The plant fossil record for this area is relatively scarce, and records from Quaternary deposits of Costa Rica overall are predominately from plant microfossils. A few plant macrofossils have been found in the Miocene (Uscari sequence; Berry 1921a) and Tertiary of Costa Rica (Puntarenas Province; Gómez 1971, 1972), but some determinations have been shown to be incorrect (Graham 1987b, 1988).

In this paper we present systematic descriptions of plant megafossils from a Pleistocene deposit along the banks of Río Puerto Viejo, on the northeastern edge of La Selva Biological Station in the canton of Sarapiquí, Heredia Province, Costa Rica. The plant fossil assemblage is based on leaves, cuticle, fruits, seeds, wood, pollen, and spores, and provides information on the composition of a lowland Atlantic flora during the Pleistocene of Costa Rica. Preliminary leaf identification, along with wood, pollen, and spore identifications were presented in Horn et al. (2003) but without systematic descriptions.