Rivet Ravine Area
There are several sections to this area of the game, and you will find a ton of different fossils here that you will need to complete your collection. To get to this area, you will need to become a level 3 fighter. When you do, you will find both Emeralds as well as Diamonds that are wroth 1500g. These both can easily help to up your money in the game and give you the cash that you need. The stumps and extra fossils will only give you 80g here, but they can add up quickly if you have a lot of them.
The normal fossils that you'll find here out in the regular areas of the game include: Alectro the water fossil, Coatlus the air fossil, and Megalo the neutral fossil.
In the Pay-to-Dig area, you'll find Angato the water fossil, Dimorph the fire fossil, Paraloph the air fossil, and Pachrino and Acro the earth fossils.
When you get to the tunnels, you'll find Stygi the fire fossil, Coatlus and Elasmoth the air fossils, Megalo the neutral fossil, and Nasaur the water fossil.
In tunnel #5, you will find Ourano the earth fossil, and the U-raptor the fire fossil.
In Mole's secret tunnel, you'll have to unlock the complete story line of Rivet Ravine to get here. But, you'll find a ton of great fossils here: Chelon and Tricera the water fossils, Zino the fire fossil, Nodo and Megath the air fossils, and Brachio the neutral fossil.
In area 1 of Rivet Ravine, you'll find Siamo the fire fossil and Goyo, Metria, and Hypsi the air fossils.
To unlock area 2, you need to finish the story line, and you'll find these four fossils: Alio the water fossil, Lambeo the fire fossil, and then Cerato and Igua the air fossils.