Which of these is the correct evolutionary line of mammals ?

Options

A. Sauropsids `rarr` Synapsids `rarr` Therapsids `rarr` Mammals
B. Sauropsids `rarr` Suropsids `rarr` Therapsids `rarr` Mammals
C. Sauropsids `rarr` Therapsids `rarr` Mammals
D. Suropsids `rarr` Therapsids `rarr` Mammals

Answer

To determine the correct evolutionary line of mammals, we need to understand the classification and evolution of these organisms. Here’s a step-by-step breakdown of the evolutionary lineage leading to mammals:

### Step 1: Identify the Origin
- The evolutionary line of mammals begins with **Tetrapods**, which are four-limbed vertebrates. This group is the ancestor of all terrestrial vertebrates.

**Hint:** Remember that all mammals are descendants of tetrapods, which indicates the transition from water to land.

### Step 2: Evolution of Amniotes
- From tetrapods, we move to **Amniotes**, which are characterized by having an amniotic egg. This group includes reptiles, birds, and mammals.

**Hint:** Amniotes are crucial for the evolution of mammals as they allowed for reproduction on land without the need for water.

### Step 3: Distinction Between Major Groups
- Within amniotes, we have two major groups: **Sauropsids** (which include reptiles and birds) and **Synapsids** (which include mammals and their ancestors).

**Hint:** Focus on the distinction between synapsids and sauropsids, as this is key to understanding mammalian evolution.

### Step 4: Evolution of Synapsids
- The synapsids further evolved into **Therapsids**, which are often referred to as "mammal-like reptiles." They exhibit characteristics that are more advanced than typical reptiles.

**Hint:** Remember that therapsids are a transitional group that shows the evolution towards mammals.

### Step 5: Cynodonts and Early Mammals
- Within therapsids, the **Cynodonts** emerged, which are considered the direct ancestors of modern mammals. They had several mammalian traits.

**Hint:** Cynodonts are crucial as they bridge the gap between reptiles and true mammals.

### Step 6: Emergence of True Mammals
- Finally, we arrive at **Mammals**, which evolved from cynodonts and possess characteristics such as fur and mammary glands.

**Hint:** The defining features of mammals are important to distinguish them from their ancestors.

### Conclusion
Putting this all together, the correct evolutionary line of mammals is:
1. Tetrapod
2. Amniote
3. Synapsid
4. Therapsid
5. Cynodont
6. Mammal

### Final Answer
The correct evolutionary line of mammals is **Sauropsid → Therapsid → Cynodont → Mammal**.