Introduction. Barro Colorado Island (BCI) is the most intensively studied tropical forest in the world. Despite the wide understanding of its plant composition and ecological dynamics, its past diversity is still unknown. Recently, numerous silicified wood samples were found in the island.
Objective. This study aims to characterize this newly found fossil megaflora using taphonomic, taxonomic, biogeographic, and paleoecologic approaches.
Methods. One hundred and twenty-one silicified wood samples were mapped and collected in BCI. Radiometric dating analyses were performed to determine the age of the fossiliferous locality. Thin sections of the fossil material with good preservation were prepared for identification purposes and ecosystem reconstructions.
Results. Dating analyses indicate that fossils were deposited during the early Miocene, around 20 to 23 million years ago. During a time in which Central Panama did not have a continuous land connection with South America, was a newly emerged land and was undergoing an intense volcanic activity. Geological analyses suggest that the fossils were deposited under a volcanic lahar flow, but only minor transportation occurred. Anatomical analyses of the prepared samples show that around 80% of the samples belong to the same morphotype, including multiple large trees. This morphotype has anatomical traits that are shared with the Southeast Asian mangrove genus: Sonneratia (Lythraceae). Today, this genus is between 10 to 30 m tall, however, tree height estimations of the fossil woods suggest that this morphotype could have reached up to 39 m of height.
Conclusions. Diversity and spatial comparisons of the fossil forest of BCI indicate a stark contrast with the modern flora and allow us to hypothesize that during the early Miocene BCI had a coastal ecosystem with no modern analogs. Currently 191 samples from another locality from the Barro Colorado Nature Monument are being analyzed and will widen our understanding of the ecological and evolutionary history of this emblematic flora.