Scientists estimate that there may be between 3 and 30 million species of animals on our planet. The exact number of species on Earth remains unknown, and new species are discovered all the time. If you're just starting to learn about animals and wildlife, it would be an overwhelming task to try and memorize species, one by one. Instead, an understanding of the main groups of animals provides a good foundation for further learning.
In this article, we'll take a look at six groups of animals, their characteristics and the types of organisms that belong to each group. Once you can place animals in one of these groups, you'll be on your way to understanding the basics of animal classification. The six basic groups of animals we'll focus on include:
- Amphibians
- Birds
- Fishes
- Invertebrates
- Mammals
- Reptiles
Amphibians
Amphibians include fascinating creatures such as salamanders, newts, caecilians, frogs, and toads. These animals' ancestors were the first to venture out from the water and adapt to life on land. Amphibian larvea are often aquatic and go through a complex metamorphosis process as they grow to adulthood. They have moist skin and do not have scales, feathers or hair. Find out more: Amphibians
Birds
Birds, animals best known for their ability to fly, are unmatched in their command of the skies. Birds are unique creatures having wings, feathers, hollow bones, and other adaptations for an arial lifestyle. Flight consumes a great deal of energy and consequently these warm-blooded animals have high metabolic rates. Many of their bones are fused for strength and stability. Birds are vertebrates, which means that they are among those animals that posess a backbone. They range in size from the minute Cuban bee hummingbird to the grand ostrich. Find out more: Birds
Fishes
Fish are vertebrates (they posess a backbone) that live and breath in water. Most fishes breath through specialized organs called gills and most have scales and fins. There are two major groups of fishes, bony fishes and cartilaginous fishes. Find out more: Fishes
Invertebrates
Invertebrates are an extraordinarily diverse group of animals. Invertebrates do not have a backbone, nor a bony skeleton. This large group of animals includes sponges, cnidarians, flatworms, roundworms, segmented worms, mollusks, echinoderms, and arthropods. Insects, a group of arthropods, are the most diverse group of organisms on the planet, with 900,000 species identified and an estimated 29 million more still to be identified. Find out more: Invertebrates
Mammals
This group of animals, to which humans belong, is the most familiar to us. Mammals are characterized by mammary glands, hair, a diaphram, a four-chambered heart, and a large cereberal cortex. 70 million years ago when reptile diversity declined, mammals took over habitats once unavailable to them. Find out more: Mammals
Reptiles
Reptiles are cold-blooded vertebrates that evolved from amphibians about 340 million years ago. There are two characteristics that distinguished early reptiles from amphibians and enabled them to colonize terrestrial habitats more extensively than their ancestors, scales and the ability to lay hard-shelled amniotic eggs. Scales protect reptiles from abrasion and loss of body moisture. Hard-shelled eggs provide a protective environment in which the embryo can develop. Find out more: Reptiles
