Question

Which fossil group is commonly used as an index fossil of the Mesozoic era?

• A. Trilobites
• B. Brachiopods
• C. Ammonites
• D. Graptolites

Hint:

{Trilobites = Paleozoic}, {Ammonites = Mesozoic}. Remembering era–fossil pairs helps in quick elimination.

Answer 1

The Correct Option is C

Step 1: Understanding index fossils.
Index fossils are fossils of organisms that lived for a relatively short geological time span but were widely distributed geographically. Such fossils are extremely useful for correlating and dating rock layers.
Step 2: Fossil groups and geological eras.
Different fossil groups are characteristic of specific geological eras. Trilobites are typical of the Paleozoic era, while Graptolites are mainly associated with the Ordovician and Silurian periods.
Step 3: Identifying the Mesozoic index fossil.
Ammonites evolved rapidly, were abundant, and had a wide geographic distribution during the Mesozoic era. Their rapid evolutionary changes make them excellent index fossils for this era.
Step 4: Conclusion.
Since ammonites are widely used to identify and correlate Mesozoic rock sequences, the correct answer is (C) Ammonites.