Question

Scientists studied the evolution of ancient organisms known as trilobites. An image of a trilobite is shown, and some of its body structures are labeled.

rings, eye, tail, head,

Scientists collected fossils of one species of trilobite that were determined to have lived during a 2-million-year span. The scientists observed that, over time, the number of rings in the trilobites’ tails changed. The graph shows the results of this investigation.

Time ( millions of years), x, average number of rings on tail, y, w, x, y, z,

Which labeled section of the graph represents a time when the environment where trilobites lived was changing rapidly?
A
Section W
B
Section X
C
Section Y
D
Section Z

Answer 1

B Section X

Section X shows the steepest change in the average number of tail rings over a short time. Rapid changes in a trait like this imply strong selective pressure from a quickly changing environment.