Digging into a section of preserved sediments on Swan's Bay Island in Panama's Bocas del Toro region, Smithsonian Tropical Research Institute Paleoecologist Aaron O'Dea searches for 2 million-year-old fossils of cupuladriid bryozoans, tiny filter-feeding marine animals. Using these fossils, O'Dea and other Smithsonian scientists are piecing together the ancient geological and biological history of the Isthmus of Panama. (Photo by Marcos Guerra)