Which one of the following is not a living fossil?

Options

A. Peripatus
B. King crab
C. Arcaheopteryx
D. Sphenodon

Answer

To determine which of the following options is not a living fossil, we need to analyze each option based on the definition of a living fossil. A living fossil is a living organism that has remained relatively unchanged over millions of years and has survived through various environmental conditions.

### Step-by-Step Solution:

1. **Understand the Definition of Living Fossils**:
- Living fossils are organisms that have existed for millions of years and have not undergone significant evolutionary changes. They are still alive today.

2. **Analyze Each Option**:
- **Option A: Peripatus**:
- Peripatus is considered a living fossil. It is a worm-like organism that has characteristics of both arthropods and annelids. It has been around for approximately 570 million years and has not changed significantly over time.

- **Option B: King Crab**:
- King crab is also a living fossil. It belongs to the phylum Arthropoda and has existed for about 400 million years. It has retained its form and characteristics over this extensive period.

- **Option C: Archaeopteryx**:
- Archaeopteryx is not a living fossil. It is an extinct species that served as a transitional form between birds and reptiles. Since it is no longer alive, it does not fit the definition of a living fossil.

- **Option D: Sphenodon**:
- Sphenodon, also known as tuatara, is a living fossil. It is a reptile native to New Zealand and has existed for around 200 million years, showing little evolutionary change.

3. **Conclusion**:
- Based on the analysis, the organism that is not a living fossil is **Archaeopteryx** (Option C).

### Final Answer:
**Option C: Archaeopteryx is not a living fossil.**