The hero first meets him disguised as a Fossil Center employee, in Greenhorn Plains, guarding what will later become a Pay-To-Dig site. He tells the hero that there are many rare fossils up ahead, and insists on taking your Dino Medals, saying that "Battles might damage the fossils." After the hero talks to Rosie, they realize that the area is void of fossils, containing only useless black rocks. The two go back to the fence and find the hero's Dino Medals on the ground. Rosie says that the thief must have simply tossed them aside because the hero is a rookie, and his Vivosaurs are low-level. She says that she had 10 Dino Medals, and they are now all gone (something that should be impossible as Fighters can only carry five Dino Medals at any given time).
Rosie and the hero go to the police station and tell Captain Bullwort about the thief. Rosie suggests that they go to the Fossil Stadium, and she sees a Fighter using her Vivosaurs (how she knows they're hers is unknown. All Vivosaurs of one species look exactly the same in Fossil Fighters). The hero battles P.B. Jay, who is using Rosie's weakest Vivosaurs. After the battle, Rosie confronts him, and he tells her he bought them from Medal-Dealer Joe, and that he would never have bought them if he knew they were stolen.
Rosie and the hero go to the Fossil Guild and talk to the Info Clerk. He tells them that Joe is back in Greenhorn Plains. The two return to Greenhorn Plains, where they find and confront Joe. Rosie asks the hero to battle him because he has her strongest Vivosaurs. However, even those are not very powerful, and the battle is usually easily won. The police arrive and arrest Joe, returning the Dino Medals he stole back to Rosie.
Joe can be found in the Park Area once the storyline is completed, and he says he has gone legit. He sells Dark Fossil Rocks containing Tryma fossils for 9,800 G a piece. This is the only way to get Tryma.