Vertebrates are a category of animals that share one important trait – they have a backbone. There are seven different groups, or classes, of vertebrates on Earth. These include amphibians, birds, mammals, reptiles, and three kinds of fish. In this post, we’ll explore these groups and find out what makes each one unique.
Before we dive in: If you’re an educator planning to teach vertebrates, great learning resources are key to deepening understanding! I think you and your students will love my 5 units on vertebrate classes, which you can also find within my complete Vertebrates Bundle (plus you’ll support my blog with your purchase! ❤️)
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Fish
Fish are a large and diverse group of vertebrates. Technically, they’re actually three groups of vertebrates. The three main types of fish are jawless fish, cartilaginous fish, and bony fish. Many animals that we might not always think of as fish belong to these groups. For example, sharks, skates, and rays are all types of cartilaginous fish. The bony fish group includes fish that follow the classic body plan, like salmon, tuna, and sturgeons. But this group also includes some unique fish whose bodies look quite different from their relatives – like eels and seahorses.
Fish live almost everywhere there is water—from icy mountain streams to warm coral reefs and from shallow wetlands to the deepest parts of the ocean. They range in size from tiny guppies to giant sharks and manta rays. Some fish, like tuna, are streamlined for fast swimming across the open ocean. Others, like pufferfish or seahorses, have unusual body shapes and
move slowly among reefs and seaweed.
Their diets and lifestyles vary, too. Some fish, like sharks and tuna, are predators that hunt other animals. Others filter feed tiny plankton from the water or graze on aquatic plants and coral. Some fish, like salmon, migrate long distances between freshwater and the ocean, while others spend their entire lives in one small pond. Regardless of size, shape, or habitat, fish
show an incredible range of adaptations that allow them to survive in aquatic habitats all around the globe!
Fish Traits
- Spine
- Typically cold-blooded (some exceptions)
- Gills
- Fins
- Lateral line (sensory organ)
- Found in water
Examples of Fish
- Trout
- Tuna
- Seahorse
- Eel
- Coelacanth
- Shark
- Stingray
- Lamprey
Amphibians
Amphibians come in many shapes and sizes—from long-tailed salamanders to tailless frogs and even legless caecilians! Some are huge, like giant salamanders that grow to nearly six feet (two meters) long, while others are so tiny they could sit on your pinky finger. Amphibians also display striking colors, like the brightly patterned fire salamander or the brilliantly hued—but toxic—poison dart frog.
Amphibians all share a few key traits. One of their most distinctive features is their moist, scale-free skin. To stay hydrated, amphibians usually live in damp environments or near water. Their skin contains special mucus glands to keep it moist. It’s also permeable, allowing water and gases to pass through. This means amphibians can absorb water and even breathe through their skin! However, most species also have lungs or gills for breathing.
Another trait of amphibians is metamorphosis—a dramatic transformation during their life cycle. For example, a tadpole with gills and a tail changes into an adult frog with lungs and legs. Finally, adult amphibians are carnivores, feeding on insects and other small animals.
Amphibian Traits
- Spine
- Cold-blooded
- Moist skin with no scales
- Skin surface breathing (may also have lungs and/or gills)
- 0-4 legs
- Carnivorous predators as adults
- Metamorphosis (in many species)
Examples of Amphibians
- Frog
- Toad
- Salamander
- Caecilian
Reptiles
While reptiles and amphibians may look similar, they each represent a distinct vertebrate group. Reptiles can’t breathe through their skin like amphibians. Instead, reptiles always breathe through 1 or 2 lungs, and their skin is dry and scaly. Reptiles also never go through metamorphosis the way many amphibians do.
Reptiles are not the easiest group to define. There is a lot of diversity within this group. From legless snakes to shelled turtles and armored crocodiles, the reptile group has some incredible creatures. Unlike other classes of
vertebrates, scientists now know that the group we call reptiles is not an isolated evolutionary lineage. This means that despite their many similarities, some members of the reptile group are not quite as closely related as people once thought they were. Additionally, we now know that birds descended from a reptile ancestor – so in a way, birds and reptiles are relatives!
Turtles, tortoises, crocodilians, lizards, snakes, and tuataras are all types of reptiles. They live in freshwater, oceans, and on land. They come in all sizes: from the tiny Brookesia nana chameleon at less than an inch (~2 cm) in length, to giants like Komodo dragons and crocodiles.
The saltwater crocodile is the largest reptile on earth today, measuring over 20 feet (6 meters) long! In the past, even larger reptiles roamed the Earth (dinosaurs) but today they are extinct. All in all, there are over 10,000 amazing species of reptiles alive on Earth today.
Reptile Traits
- Spine
- Cold-blooded
- Scales or scutes
- 0-4 legs
- Breathe air with 1 or 2 lungs
Examples of Reptiles
- Lizard
- Snake
- Turtle
- Crocodile
- Alligator
- Tuatara
Birds
Birds are a group of egg-laying, warm-blooded vertebrates with feathers, wings, and beaks. If you traced that family tree back far enough, you’d discover that birds evolved from theropod dinosaurs. Because of this shared ancestry, a sparrow is actually more closely related to a dinosaur than to a mammal, amphibian, or any other living vertebrate class. Scientists use these evolutionary relationships to decide which animals belong in the bird group.
Birds live on every continent, including Antarctica, and can be found in nearly every habitat—from forests and deserts to wetlands and open oceans. There are over 10,000 species of birds, and they range in size from tiny hummingbirds to towering ostriches. Birds also show remarkable diversity in behavior. Some migrate thousands of miles each year, while others stay in the same place their entire lives. Their colors, calls, and nesting styles vary just as much as their sizes and shapes.
Bird Traits
- Spine
- Warm-blooded
- Breathe air with lungs
- Lay eggs
- Feathers
- Scutes on legs
- Beak
- Wings (many fly, but not all)
Examples of Birds
- Turkey
- Sparrow
- Ostrich
- Penguin
- Woodpecker
- Goose
- Heron
- Owl
Mammals
Like birds, mammals are warm-blooded vertebrates. Mammals are unique because they have hair/fur and nurse their babies with milk. There are over 5,000 different species of mammals alive today. They live in freshwater, oceans, on land, and even take to the skies! They come in all sizes, from tiny creatures like the bumblebee bat to giants like whales. The blue whale is not only the largest mammal, but also the largest animal on earth!
Mammal Traits
- Spine
- Warm-blooded
- Breathe air with lungs
- Fur, hair, or whiskers (on all or part of the body, for at least part of its life)
- Produce milk (in females)
- Single lower jawbone
- 3 tiny earbones
Examples of Mammals
- Mouse
- Deer
- Tiger
- Whale
- Otter
- Bat
- Armadillo
- Kangaroo
- Human
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