LEAVES FROM THE SEA: A FLORA FROM THE PLIOCENE BOWDEN FORMATION OF JAMAICA

The 3.5 million-year-old Bowden shell bed of the Bowden Formation in southeast Jamaica is one of the richest fossil sites in the Antilles, yielding a highly diverse Pliocene fauna. More than 850 taxa are known from the mixed terrestrial and marine molluscan assemblage, but only two species of ‘plants’, both marine calcareous algae, have been described to date. In previous descriptions of the section, plant fragments have been mentioned, but specimens have not been illustrated or described. Here, we report the first fossil leaf flora from the Bowden Formation, and from Jamaica more generally.

Over 300 leaves were collected from fine-grained 'marlstones' between the shelly and cobble-rich conglomerates layers from the Bowden Formation type section. Leaves were found both isolated and within concentrated leaf layers. Almost all of the leaves, with the exception of those from the leaf layers, were non flat-lying, non- parallel bedded; instead, the leaves were found in random orientations, sometimes with evidence of folding, reflecting a tumultuous burial. The leaves are often preserved as iron-stained impressions; a few have thicker iron coatings and retain some evidence of external morphology, such as stomata and epidermal cell shape, visible under the scanning electron microscope. No internal anatomy or organic cuticle was found in any of the fossils collected.

Leaves were identified to morphotype based on a combination of leaf shape, venation, and the presence of unique characters such as a drip tip; a total of 20 morphotypes were assigned. The leaves are often fragmentary and higher order venation is rarely preserved, making taxonomic identification difficult. However, some leaves are whole and/or retain a large suite of characters. Preliminary investigations have identified common elements of tropical vegetation, including representatives of Fagacaeae, Lauraceae, and red mangrove, Rhizopora mangle. The assemblage is allochthonous and represents a mixed regional assemblage of both coastal and more inland taxa.