Question: A geologist found fossils of horse bones in different rock layers of a canyon. The fossils in the lower levels show shorter bones than those in the upper-level fossils. Which conclusion is based on the geologist's observations?
Choices:
Horse's reproduce using two parents.
Horse's became larger over time.
Smaller Horse's went extinct, and then larger Horse's formed.
Smaller Horse's are better suited to the environment than larger Horse's.
Answer: B