Are saltmarshes younger than mangrove swamps?

Temperate saltmarshes and tropical mangrove swamps (mangals) are marine‐influenced, productive ecosystems that enhance nutrient transfers between land and sea and facilitate colonization of lineages between terrestrial and marine habitats. Mangals have existed since the late Cretaceous, but the time of origin of saltmarshes is less clear. On the basis of phylogenetic and fossil evidence for plants and molluscs specialized to these ecosystems, I propose that saltmarsh vegetation of angiosperms began during the latest Eocene to Early Oligocene (35–30 Ma), at least 34 m.y. after the origin of mangals. The plants that colonized saltmarshes then and later have mainly temperate origins, contrasting with the tropical‐forest origins of mangroves. Unlike the plants, the few saltmarsh‐specialized molluscs are derived from tropical lineages and reflect recent colonizations. The development of saltmarshes during the Neogene enhanced near shore productivity along temperate and Arctic coastlines.