I have a request for a fossil but don't know how to get them, I'm on level 43 and as yet have nothing..

Okay so for this quest you’ll need the ‘mysterious letter’ item, and then you’ll need to merge them until level 3 for a map to an island, if i’m not mistaken. From there you can get the fossils. Mysterious Letters can be obtained via the shell bucket, but only rarely.

After you getting the island, island will give you a one part of the mysterious fossil. Then you have to complete 10 orders. After completing 10 orders, you will receive another part of a fossil. Then you will see there is an order of both two parts, when you complete the order you will get the mysterious fossil(full) as a reward.