Historical biogeography of Middle-East mangroves: paleobotanical evidence

Valentí Rull 

This paper reconstructs the origin, diversification, and decline of Middle East (ME) mangroves from the Late Cretaceous to the present using the MESMA database, a comprehensive compilation of fossil pollen and macrofossil records integrated with paleogeographic, tectonic, climatic and sea-level evidence. To date, global paleobiogeographical and evolutionary syntheses of mangroves have emphasized the role of the ME region as either a dispersal corridor or a biogeographical barrier, rather than as a research focus in its own right. The earliest reliable ME mangrove records correspond to Nypa from the Late Cretaceous, when the present-day Arabian Peninsula formed part of the Nubian Plate along the southern Tethyan margin. A potential Albian precursor suggests that the ME may have played a role in the early evolution of the Nypa lineage, which, if confirmed, would represent the earliest mangrove record worldwide. Mangrove diversification began in the Eocene with the arrival of Avicennia and Acrostichum, followed by Rhizophora in the Oligocene, leading to the highest diversity levels recorded in the region. This diversification is remarkable because it occurred during the Eocene/Oligocene transition, a phase associated with mangrove decline in most other parts of the world. A major biodiversity crisis took place during the Middle Miocene, when regional desertification associated with the Middle Miocene Climatic Transition, likely linked to the Arabia–Eurasia collision and the resulting closure of the Tethys Sea, caused the disappearance of most mangrove elements, leaving only Avicennia and Rhizophora as surviving mangrove-forming taxa. This event established the low-diversity pattern that characterizes present-day ME mangroves. Quaternary records are scarce, but Holocene sequences from southern Arabia document a pronounced reduction of Rhizophora between approximately 6.5 and 4.5 ka BP, coinciding with the termination of the Holocene Humid Period, after which the genus survived only in a few relict areas, whereas the more stress-tolerant Avicennia persisted and became dominant. In contrast to previous studies, this synthesis identifies the ME as a significant region for mangrove evolution per se, rather than merely in relation to other biogeographical regions. The study also highlights substantial gaps in the fossil record and several unresolved questions that provide promising avenues for future research.