Animals are the most advanced organisms on the planet. The first animals are thought to have evolved over 550 million years ago and they have since spread to all corners of the globe and diversified into millions of species.
Animals can be distinguished from other living things by the combination of three features: 1) they are unable to make their own food; 2) they have multiple cells; and each cell has a nucleus and other specialized structures called organelles. Scientifically put, animals are heterotrophic, multicellular organisms with eukaryotic cells.
Animal species are often split into vertebrates and invertebrates – two very broad categories of animals. Vertebrate species are animals that do have a backbone such as humans, birds, fish and reptiles and make up the majority of large land animals.
Invertebrate animals lack a backbone and often have a skeleton on the exterior of the body. The majority of animal species are classed as invertebrates and many you will be familiar with such as insects, jellyfish, worms and spiders.
Mammals are a group of warm-blooded vertebrates and include the largest and smartest animals on the planet. They are distinguished from other animals by having hair or fur and mammary glands for milk production.