The fossil record shows that some animals, such as the horseshoe crab, have existed unchanged for millions of years. Other organ
isms, such as pigs, have undergone a well-documented sequences of changes. Which type of organism would be most useful as an index fossil? Explain your answer.
An index fossil is an animal or plant that is preserved in rock record of the earth and has a characteristic of a certain period of geologic time or environment. A useful index fossil must be abundant, easily recognizable, and have a geographic distribution.
<em><u>Pigs would be a useful index fossil because the well-documented changes that occurred in the fossil record would help geologists determine the ages of rocks much more than the unchanging horseshoe crabs.</u></em>