In their analysis, the researchers wanted to figure out how these red mangroves were able to flourish in the freshwater along the San Pedro River in the Mexican state of Tabasco. Red mangroves, or Rhizophora mangle, usually only grow in saltwater along tropical coastlines; this forest was too far from the coast for these trees to have access to saltwater.
Using genetic, geologic, and vegetation data along with models of historic sea levels, the scientists determined that the forest actually began growing in the region some 125,000 years ago, when the oceans extended significantly farther inland. This period, known as the Penultimate Interglacial Period, was a short warm period in between eras of glaciation. Although the waters receded as the world changed, the mangrove forest, incredibly, remained.
