There are 20 Fossils spread out around the island.
Newton's Lab1) Next to the blue electric gate.
Carnivore Cove2) Behind the Recycle Machines
3) Under the waterfall (you can walk on the water here)
Between Carnivore Cove and Lava Falls
4) In midair after destroying the amber, use T-Rex to collect it
Lava Falls5) On top of a rock formation over the lava, clean the area to gain access.
Frosty Fields6) Behind Coin Deposit Machine
7) Climb up the rock formation in the water next to #6
Ice Age Pass8) Inside tree tunnel after clearing the area
Venus's Lair9) Behind Venus Debt Trap
Redwood Coast10) Midair next to Tax Machine, quickly summon T-Rex with
and then
to reach.
11) Under tax bridge
Bird Bay12) In the corner next to the water
13) On the rock platform directly above Bird Bay, accessible after unlocking Pteranodon
Out At Sea14) On top of tall rock platform directly opposite Bird Bay
15) Fly through the caves to the right of #14
16) On three small platforms directly opposite the tax bridge
Amber Cliffs17) In cave opening above Amber Cliffs, visible as you fly in for the first time.
18) Directly below #17 on the coast
19) Behind the giant tree with the trapped key
Exit Island20) Just past the gold gate to the left