Bats and whales are considered mammals because they share several key characteristics with other mammals. These characteristics include:
1. Mammary Glands: All mammals, including bats and whales, have mammary glands that produce milk to nourish their young.
2. Hair/Fur: Most mammals, including bats and whales, have hair or fur on their bodies that provides insulation and protection.
3. Warm-Blooded: Mammals are warm-blooded, meaning they can regulate their body temperature internally, which allows them to live in a wide range of environments.
4. Three Middle Ear Bones: Mammals have three middle ear bones, which help to transmit sound waves from the outer ear to the inner ear. This allows for a more efficient hearing mechanism.
5. Live Birth: Most mammals give birth to live young, rather than laying eggs.
Bats and whales are also unique in their adaptations to their specific environments. Bats are the only mammals capable of sustained flight, which has allowed them to occupy a unique ecological niche. They have wings formed from modified arms and elongated fingers that are covered with skin, forming a lightweight and flexible membrane that enables them to fly.
Whales, on the other hand, are adapted to life in the water. They have streamlined bodies, a layer of blubber for insulation, and powerful tail fins for propulsion. Their limbs have been modified into flippers, and their nostrils have moved to the top of their head to form a blowhole, which allows them to breathe while swimming.
In conclusion, bats and whales are considered mammals because they share key characteristics with other mammals, such as mammary glands, hair/fur, warm-bloodedness, three middle ear bones, and live birth. They are also adapted to their unique environments in ways that make them highly specialized and successful in their ecological niches.