The diagram below represents a series of rock layers found at a particular location. Each different type of shape shown in the layers represents a fossil of a different species.

Suppose each symbol is related to a particular species in the following ways:
A red triangle represents a species of marine crustacean.
A green circle represents a species of jawless fish.
A yellow square represents a species of tree moss.
A purple star represents a species of forest-dwelling insect.
The change shown in the diagram at the end of the Devonian geologic period could best be explained by
A.
the melting of a glacier and development of freshwater lakes and rivers.
B.
the arrival of a new predator in the ecosystem.
C.
the environment changing from ocean to dry land.
D.
the environment changing from a cold climate to a warm climate.