A new perspective on the origin of Neotropical mangroves

Mangroves are forested ecosystems that dominate tropical and subtropical coasts all over the world. Currently, these ecosystems are thought to have originated in the Cretaceous, on the coasts of the former Tethys Sea, and evolved into divergent Paleotropical and Neotropical mangrove communities after the closure of this pantropical sea. However, a fresh reconsideration of the available fossil pollen evidence from the Neotropical region suggests a different evolutionary framework.

According to the new conception, which will be published soon in the journal Earth-Science Reviews, the emergence of mangrove communities in the Caribbean region, the cradle of Neotropical mangroves, occurred in the Eocene and constituted an evolutionary novelty with no Cretaceous precursors. Actually, no reliable evidence has been found for the occurrence of Caribbean mangrove communities before the Eocene, when Neotropical mangroves originated de novo disconnected from the Paleotropical realm.

Distribution of mangroves (in red) around the world. The Caribbean region is highlighted by a green box. Image source

The keystone development for the origin of Neotropical mangroves was the evolutionary appearance of mangrove-forming trees, without which mangrove ecosystems cannot exist at all. In the Caribbean region, the first mangrove-forming tree was the Eocene ancestor of the present tea mangrove (Pelliciera rhizophorae), which is now restricted to a small region of Central America but was widespread across the Neotropics during the Eocene. Tea-mangrove trees acted as “condensation nuclei” for the organization and development of these novel ecosystems by recruiting species pre-adapted to tidal conditions, which led to the formation of the typical composition and structure of mangrove communities.

Tea mangroves (Pelliciera rhizophorae) from Costa Rica, Central America. Image source

This novel and challenging evolutionary scenario would lead to the reconsideration of current theories about the origin and evolution of mangroves on a global scale, as most of them are based on the still undemonstrated existence of hypothetical Cretaceous precursors.

Reference

Rull, V. 2022. The Caribbean mangroves: an Eocene innovation with no Cretaceous precursors. Earth-Sience Reviews, doi 10.1016/j.earscirev.2022.104070.

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