First mammal occurred in which eral period?

Options

A. Permian-Palaeozoic
B. Triassic-Mesozoic
C. Tertiary-Coenozoic
D. None of these

Explanation

**Step-by-Step Solution:**

1. **Understanding the Question:** The question asks about the first occurrence of mammals and the specific geological period in which this event took place.

2. **Identifying the Relevant Eras and Periods:**
- The geological time scale is divided into eras and periods. The two main eras relevant to this question are the Paleozoic Era and the Mesozoic Era.
- The Paleozoic Era includes the Permian period, while the Mesozoic Era includes the Triassic, Jurassic, and Cretaceous periods.

3. **Examining the Permian Period:**
- The Permian period is the last period of the Paleozoic Era, which existed approximately 28.6 crore years ago.
- During this period, mammal-like reptiles emerged, but these were not true mammals.

4. **Transition to the Mesozoic Era:**
- Following the Paleozoic Era, the Mesozoic Era began, which is known as the "Age of Reptiles."
- The Mesozoic Era includes the Triassic period, which is significant for the emergence of true mammals.

5. **Identifying the Triassic Period:**
- The Triassic period is the first period of the Mesozoic Era, existing around 24.8 crore years ago.
- During this period, the first true mammals appeared, known as prototherian mammals, which were oviparous (egg-laying).

6. **Conclusion:**
- Based on the information, the first mammals occurred during the Triassic period of the Mesozoic Era.

**Final Answer:** The first mammals occurred in the Triassic period of the Mesozoic Era.

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