Studies in Neotropical Paleobotany. VI. The Lower Miocene Communities of Panama-the Cucaracha Formation

Abstract

The Cucaracha microfossil flora is the third in a series of four lower Miocene assemblages studied from southern Central America (Uscari.sbd.Costa Rica; Culebra, Cucaracha, La Boca.sbd.Panama). Nineteen palynomorphs have been identified (Selaginella, monolete fern spores types 1-3, Cyathea, Ceratopteris, Pteris, cf. Antrophyum, trilete fern spores types 1-2, Crysophila and Manicaria-type palm pollen, Ilex, Compositae, Alchornia, Alfaroa/Engelhgardia, Curida, Eugenia/Myrcia, and Rhizophora). The paleocommunities include a fern marsh, with associated palms, fringed seaward by mangroves, and bordered on the surrounding uplands by versions of the tropical wet, tropical moist, and premontane forests. Evidence for higher-altitude vegetation and communities of drier to arid aspect (open forests, savannahs) continues to be meager for Tertiary floras in the region. Affinities of the flora are distinctly Central and North American, consistent with other paleontological and biogeographic data, as well as paleophysiographic reconstructions for southern Central America. Paleoclimatic conditions were similar to those presently prevailing in coastal, lowland, and mid-altitude (1,200-1,500 m) habitats. Frequent and extensive volcanic activity documented for the region likely disrupted the vegetation, resulting in a shifting mosaic of short-term, more open communities. This may account for a paleobotanical record reflecting primarily dense forests on the slopes, while the few fossil mammalian faunas contain remains of browsers and grazers, suggesting more open forests and savannahs.