7 Types of Animals That Make Our Planet Cool to Live On

Mammals are warm-blooded animals that typically have hair or fur and feed their young with milk. Humans, dogs, and horses all belong to this group. Most mammals have four legs and give birth to live young, though there are exceptions like the egg-laying platypus.

Birds are defined by feathers, beaks, and the ability to lay eggs. Many can fly, but not all; ostriches and penguins are flightless. Birds and crocodilians (such as crocodiles and alligators) share a common ancestor, making them evolutionary cousins. Birds inhabit nearly every land environment on Earth.

Reptiles are cold-blooded animals with scaly skin. This group includes turtles, snakes, lizards, and crocodiles. Most lay eggs and are well-adapted to land habitats — though some, like sea turtles, spend much of their life in water.

Frogs, salamanders, and newts are amphibians. They begin life in water with gills and transform into air-breathing adults. Amphibians are sensitive to environmental changes, making them important indicators of ecosystem health.

Fish were the first vertebrates on Earth. Most live in water their whole lives, breathing through gills. Fish come in three basic types: jawless, cartilaginous (like sharks), and bony fish (like trout). All these animals play key roles in aquatic food webs.

Invertebrates are animals without backbones and make up the majority of animal species. They include:

Technically a subgroup of invertebrates, arthropods deserve their own spotlight. This includes insects, crustaceans, and arachnids like spiders. They’re the most diverse group in the animal kingdom, occupying nearly every habitat.

We created this article in conjunction with AI technology, then made sure it was fact-checked and edited by a HowStuffWorks editor.