Fossil

Fossils are naturally occurring objects. They appear in the background walls, and you can excavate them with tools crafted at Fossil Station, such as Basic Fossil Brush. If successful, you receive: 1) valuable loot, 2) the fossil itself (decorative object).

Fossils are very common on the first Garden planet.

Differences from vanilla

Fossils are a vanilla mechanic (see vanilla wiki for how they work in vanilla), but FU makes a number of changes:

you receive more loot if a fossil is successfully excavated.
successfully excavating a fossil always yields Research Data.
failing to excavate a fossil will yield some Bone.
there are more fossils, including 4 "large" fossils (for Large Fossil Display).
there are X-Large Fossil Display and Huge Fossil Display that can house even larger fossils (however, no such fossils are currently added by FU: Large Fossil Display is enough for everything). You can place a smaller fossil into these two displays.
there are two more brushes: Fossil Hammer (provides the excavation mini-game with imprecise but powerful instruments) and Microparticle Brush (even more precise than Master Fossil Brush, which was the best brush in vanilla).
Fossil Station is cheaper in FU (requires tier 1 Iron, in vanilla it was tier 2 Tungsten).

Troubleshooting

If brush doesn't start a mini-game, make sure that:

You are standing very close to the fossil,
You are not trying to excavate Bone (ore), which is sometimes mistaken for fossils. Actual fossils look like this: