Step-by-step explanation:
Palaeontologists study the fossil and once they found that the fossil of an organism in layer 2 and 3. The fossil present in layer 3 is very similar to the fossil present in layer 2.
From this, it could be concluded that the layer 3 possible might be evolved from the fossil present in layer 2. The fossil of layer 3 might be a close relative of the extinct fossil of layer 2 as they could have shared a common ancestor.
Many possibilities could be explained but these two are more valid.