Pelycosaurs and Therapsids were

Options

A. Sauropsids
B. Synapsids
C. Sphenopsids
D. Dinosaurs

Answer

**Step-by-Step Solution:**

1. **Identify the Groups**: The question asks about Pelycosaurs and Therapsids. We need to categorize these two groups correctly.

2. **Define Pelycosaurs and Therapsids**:
- Pelycosaurs are an early group of synapsids that lived during the late Carboniferous to the early Permian periods. They are characterized by their large dorsal sails and are often considered the ancestors of mammals.
- Therapsids evolved from Pelycosaurs and are often referred to as "mammal-like reptiles." They lived during the late Permian to the Triassic periods and are significant in the evolution of mammals.

3. **Determine Their Classification**: Both Pelycosaurs and Therapsids belong to the group known as synapsids. This classification is important because it distinguishes them from other groups such as sauropsids (which include reptiles and birds).

4. **Characteristics of Synapsids**:
- Synapsids are characterized by having a single temporal fenestra (an opening in the skull behind the eyes), which is a key feature that differentiates them from diapsids (like reptiles).
- They have evolved traits that are unique to mammals, such as a more advanced skeletal structure and adaptations for regulating body temperature.

5. **Conclusion**: Therefore, Pelycosaurs and Therapsids are classified as synapsids, which are the ancestors of modern mammals.

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