Why are whales not grouped in fishes?

Explanation

### Step-by-Step Solution:

1. **Classification of Whales**: Whales are classified under the class Mammalia, which includes all mammals. This classification is based on specific characteristics that whales possess.

2. **Warm-Blooded vs. Cold-Blooded**: Whales are warm-blooded animals, meaning they can regulate their body temperature regardless of the surrounding environment. In contrast, fishes are cold-blooded and do not have this ability.

3. **Heart Structure**: Whales have a four-chambered heart, which is a characteristic of mammals. Fishes, on the other hand, typically have a two-chambered heart.

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