A Note on Paleobotany of Mangroves

Abstract

There is little published research on the paleobotany of mangroves. According to Rollet (1981), from 1600-1975 the number of papers on the topic was 126, which was 2% of the 5,653 papers on mangrove research published in that period. Research on mangrove paleobotany since 1976 has also been minimal. We collected and reviewed papers on the paleobotany of mangroves, visited museums to obtain information on fossils, mainly pollen, and analyzed the collected data. The results are described below.

The first mangroves appeared during the Upper Cretaceous era, 100-65 million years ago (mya). The evolution of mangroves is thought to have been strongly related to sea-level change (transgression-regression cycles) in geological times. Some woody angiosperms growing in freshwater swamp forests succeeded at growing in tidal areas and acquired salinity tolerance when the vast extent of those areas underwent marine transgression. That event happened not only once but likely several times after the Upper Cretaceous, and each time the biodiversity of mangroves became richer. The origin of present mangroves can be divided into two groups, the Old and New (Worlds, and we predicted that the two mangrove groups could also be found in the period of the Upper Cretaceous. There were several questions we could not resolve, for example, how the expansion of their distribution proceeded. Mangrove propagules are spread by sea currents and they expand their habitats. The world’s seas were connected during the time from the Upper Cretaceous, when the first mangroves appeared, to the Miocene, when the Tethys Sea closed. Nevertheless, we assume that for over 80 million years, the Old and New Worlds did not mix. Genetic research on the migration and evolution of mangroves will be essential for complementing fossil studies.