The Caribbean mangroves: An Eocene innovation with no Cretaceous precursors

The mangrove communities of the Caribbean region are considered descendants of former pantropical Late Cretaceous mangroves that underwent regional differentiation after the tectonic closure of the Tethys Sea. The southern Caribbean area has been considered the cradle of Neotropical mangroves. These inferences were based mainly on qualitative evidence, such as the presence/absence of fossils showing botanical affinities with present-day mangrove taxa. However, as demonstrated in Quaternary paleoecology, the most suitable approach for reconstructing past plant communities is the assemblage approach, which is based on quantitative palynology. Therefore, the problem of the origin of Caribbean mangroves, as ecological communities, is addressed here by reviewing in detail the Late Cretaceous to Eocene quantitative palynological studies available for the region to properly reconstruct past mangrove assemblages. No evidence has been found for the occurrence of mangrove ecosystems during the Late Cretaceous and the Paleocene, only records of the fossil representatives of some individual taxa (Nypa, Acrostichum), which are not mangrove-forming elements and, hence, are not reliable indicators of mangrove communities. The first robust evidence of true mangrove communities was found in the Middle Eocene (Lutetian). These mangrove communities were dominated by the fossil representative of Pelliciera, a mangrove-forming tree with a Neotropical distribution by that time. Back-mangrove communities were dominated by the palm Nypa (which was pantropical by that time but is now restricted to the Indo-Malayan region), the fern Acrostichum and palms, notably Mauritia, along a sea-land saline to freshwater community gradient. Pelliciera originated in the southern Caribbean during the Early Eocene and became dominant in the Middle Eocene, when it dispersed across the Caribbean area, probably favored by the migration of the Caribbean plate. Therefore, the first Caribbean mangroves were ecological and evolutionary innovations that emerged de novo during the Eocene, rather than a consequence of the regional evolutionary differentiation from hypothetical Late Cretaceous Tethyan mangroves, whose existence is not supported by quantitative palynological records. It is proposed to develop this type of study for other tropical/subtropical mangrove communities, for a sounder view of mangrove origin and evolution, at a global scale.