Studies in Neotropical Paleobotany. IV. The Eocene Communities of Panama

Abstract

The middle(?) to upper Eocene Gatuncillo Formation outcrops near Alcalde Diaz, Panama. From layers of lignite in the formation an assemblage of fossil pollen and spores was recovered, including Selaginella, Ceratopteris, Pteris, monolete fern spores (Types 1-5), trilete fern spores (Types 1-5), cf. Tillandsia, Palmae (Types 1-5), cf. Campnosperma, Ilex, cf. Araliaceae, cf. Paragonia/Arrabidaea, cf. Protium, cf. Tetragastris, Combretum/Terminalia, Casearia, Lisianthius, cf. Tontalea, Alfaroa/Engelhardia (rare), Crudia, Malpighiaceae, cf. Ficus, Eugenia/Myrcia, Coccoloba, Rhizophora, Faramea and other Rubiaceae, Cardiospermum, Serjania, Paullinia, cf. Chrysophyllum, Pelliceria, and Mortoniodendron. Moist lowland communities, as presently occur between the Atlantic side of Gatun Lake and Pina, are well represented, whereas vegetation of higher altitudes and drier habitats is poorly represented or absent. A reconstruction of paleoenvironments, based on varied lines of biological and geological evidence, includes a series of volcanic islands of moderate to low relief, bordered seaward by shallow limestone-depositing coralline communities, and fringed by mangrove swamps of Rhizophora and especially Pelliceria. Inland communities included tropical moist, tropical wet, and premontane wet forests growing under the general tropical conditions of high rainfall (ca. 2,500 mm) and high uniform temperatures. The lowland insular environment may not record subtle climatic changes more evident in paleocommunities derived from continental areas of greater topographic relief and may reflect paleoenvironmental conditions in the immediate vicinity of the Gatuncillo depositional basin. An assessment of regional paleoclimates and paleophysiography must await discovery of other fossil floras, because the Gatuncillo assemblage is the only one of Eocene age known for northern Latin America.