In the left part of the diagram, we can see a representation of the fossils found in each layer of rock.
On the right side, there is a representation of how much the fossils have changed over time, with two periods of stasis with a rapid change in the middle.
We can see that the mollusks maintained their shape during a prolonged period, as seen in 4 of the rock layers, and then in the newer two layers, they show a very different shape.
The rapid change in the shape of the mollusks could be due to a sudden environmental change that led to the original shape having a lower fitness, and favored the new shape.
