Two characters shared by crocodiles and birds are
4-chambered heart and external fertilization
Homeothermy and 4 - chambered heart
Amniotic locomotion and megalecithal eggs
Bipedal locomotion and megalecithal eggs

Options

A. 4-chambered heart and external fertilisation
B. Homeothermy and 4 - chambered heart
C. Amniotic locomotion and megalecithal eggs
D. Bipedal locomtion and megalecithal eggs

Answer

To determine the two characters shared by crocodiles and birds, let's analyze the options provided step by step.

### Step 1: Understand the Characteristics of Crocodiles and Birds
- **Crocodiles** belong to the class Reptilia, while **birds** belong to the class Aves.
- Despite being from different classes, they share some evolutionary traits.

### Step 2: Evaluate Each Option
1. **4-chambered heart and external fertilization**:
- Both crocodiles and birds have a **4-chambered heart** (2 atria and 2 ventricles).
- However, **external fertilization** is not a characteristic of birds; they undergo internal fertilization. This option is incorrect.

2. **Homeothermy and 4-chambered heart**:
- Birds are **homeothermic** (warm-blooded), while crocodiles are **poikilothermic** (cold-blooded). Therefore, this option is incorrect.

3. **Amniotic locomotion and megalecithal eggs**:
- Both crocodiles and birds exhibit **amniotic locomotion**, which refers to movement within the egg due to the presence of an amniotic cavity.
- They also lay **megalecithal eggs**, which are eggs with a large amount of yolk. This option is correct.

4. **Bipedal locomotion and megalecithal eggs**:
- While birds are bipedal, crocodiles do not exhibit true bipedal locomotion. This option is incorrect.

### Conclusion
After evaluating all the options, the correct answer is:
**Amniotic locomotion and megalecithal eggs**.