The first mammals arose

Options

A. After the extinction of dinosaurs
B. Before the origin of dinosaurs
C. Along with the dinosaurs
D. From the dinosaurs

Explanation

### Step-by-Step Solution:

1. **Understanding the Timeline of Mammals**:
- The first mammals appeared approximately 210 million years ago. This places their origin in the Mesozoic Era, specifically in the Triassic period.

2. **Identifying the First Mammals**:
- The earliest known mammals were small, shrew-like creatures known as Morganucodon. They are considered to be among the first true mammals.

3. **Characteristics of Early Mammals**:
- Morganucodons had several mammalian characteristics, including:
- Hair covering their bodies.
- Mammary glands for nursing their young.
- A relatively small brain size compared to modern mammals.

4. **Evolutionary Context**:
- The emergence of mammals occurred alongside the dinosaurs, but they did not evolve from them. Instead, both groups share a common ancestor that existed before the rise of dinosaurs.

5. **Conclusion**:
- The first mammals arose during the Triassic period, around 210 million years ago, and coexisted with dinosaurs, but they evolved separately from them.