Of the more than 1 million species of animals on Earth, only about 5,500 are mammals. That means the rest are not mammals! Some of the most common animals that are not mammals include birds, reptiles, amphibians, fish, and insects. Each of these groups contains a vast array of different species, from the tiny hummingbird to the enormous saltwater crocodile.
Mammals are a class of vertebrate animals characterized by having hair on their skin and mammary glands for feeding their young. They also have a four-chambered heart and breathe air using lungs. In contrast, birds are warm-blooded vertebrates that have feathers instead of hair. Reptiles are cold-blooded vertebrates that have dry, scaly skin covered in overlapping plates. Amphibians are cold-blooded vertebrates that live part of their life in water and part on land. Fish are cold-blooded vertebrates that live in water and breathe using gills. Insects are invertebrate animals with six legs, three body sections, and two pairs of wings (in most cases).
So, there you have it! A quick overview of some of the main animal groups that are not mammals. Of course, this is just a small sampling of all the incredible diversity found among non-mammalian animals – there’s so much more out there to explore!