As the Pteranodon Family continues their journey underground, Don accidentally breaks Buddy's trilobite fossil (the oldest fossil in his collection!) When the search for another trilobite fossil turns up empty, their new friend Natasha Necrolestes takes them to Fossil Alley, where the kids learn that the older the fossil, the deeper underground it is. Story B Educational Objectives: You don't usually find fossils from different time periods mixed together in the Earth. The Law of Superposition means that when we see a stack of rock layers, the deeper you go into the Earth, the older the rocks and fossils you find.