A geologist observes abundant fossils of a distinctive trilobite species in a shale, but this trilobite disappears as she walks through the shale. In younger rocks, just above the horizon where the fossil disappears another species of trilobite becomes the prominent fossil in similar shales. Which conclusion is most logical for this observation?
A) A hurricane or other catastrophe killed all of the early species so the other species could move in.
B) The second, trilobite group in the upper section went extinct where the change in fossils is seen.
C) The first trilobite species went extinct and its ecological niche was occupied by another species, which may have evolved from the first.
D) The organisms whose remains form the first fossil moved from the area for unknown reasons.

Question

Quizplus · Accepted Answer

The disappearance of the first trilobite species and its replacement by a different one in a similar environment suggests that the ecological niche of the first species was taken over by a different species, which may have evolved from the first one. This is a common occurrence in the fossil record due to factors such as competition for resources, environmental changes, and evolution. There is no evidence of a catastrophe, extinction of the second trilobite group, or migration of the first species, so options A, B, and D can be ruled out.

A Geologist Observes Abundant Fossils of a Distinctive Trilobite Species