Over the past 15 years, Tony has been exploring the Isthmus. He has traveled on horseback up mountain slopes, in dugout canoes on muddy rivers, and on foot in the jungle. In his travels, Tony has made maps and drawn pictures - or “sections” - of hundreds of the Isthmus's rock layers. The sections show layers with fossils. The fossils include shark teeth, fish bones, shells, corals, and tiny plants and animals. The kind of fossils Tony finds are like the materials that settle to the ocean floor today.