Groups of vertebrates

Vertebrates are animals that have a backbone or spinal column, which provides structural support and protects the spinal cord. There are five major groups, or classes, of vertebrates:

  • Fish: Fish are aquatic animals that have gills for breathing and scales to protect their skin. They are the most diverse group of vertebrates, with over 33,000 known species.
  • Amphibians: Amphibians are cold-blooded animals that can live on land and in water. They typically have moist skin and lay their eggs in water. Examples include frogs, toads, and salamanders.
  • Reptiles: Reptiles are cold-blooded animals that are covered in scales or plates. Their eggs are laid on ground, and they require air to breathe. Examples include snakes, lizards, turtles, and crocodiles.
  • Birds: Birds are warm-blooded animals that have feathers and lay eggs. They have lightweight, but strong skeletons that allow them to fly. Examples include eagles, penguins, and hummingbirds.
  • Mammals: Mammals are hairy or furry mammals that give birth and produce milk for their offspring. They have a diaphragm to help them breathe and give birth to healthy offspring. Humans, canines, felines, and cetaceans are just a few examples.

5 Groups of vertebrates

Vertebrates vs Invertebrates

The presence or lack of a backbone is the primary defining characteristic between the vertebrate and invertebrate animal kingdoms.

Animals with a backbone or spinal column are called vertebrates, as I mentioned before in this blog. This includes fish, amphibians, reptiles, birds, and mammals. Vertebrates tend to be larger and more complex than invertebrates, with well-developed nervous systems and more advanced sensory organs.

Invertebrates, on the other hand, are animals that do not have a backbone. This includes a wide variety of animals, such as insects, spiders, snails, clams, and jellyfish. Invertebrates make up the vast majority of animal species on Earth, and they are found in almost every environment, from deep sea trenches to desert sand dunes. Invertebrates are often much smaller and less complex than vertebrates, but they can still have sophisticated sensory organs and complex behaviors.

Fish (Pisces)

Fish are aquatic vertebrates that are cold-blooded and have gills for breathing. They are found in a variety of aquatic environments, from freshwater to saltwater, and from shallow streams to the depths of the ocean.

Fish are characterized by their streamlined bodies, fins, scales, and swim bladder, which helps them control their buoyancy. Examples of fish include salmon, trout, sharks, and tuna.

Characteristics of Fish

Fish are aquatic vertebrates that have several characteristics that set them apart from other animals. Some of these characteristics include:

  • Scales: Most fish have scales that protect their skin and reduce drag as they swim through water.
  • Fins: Fish have fins that help them maneuver in water, such as the dorsal fin on their back and the pectoral fins on their sides.
  • Gills: Fish breathe through gills, which extract oxygen from water as it flows over them.
  • Swim bladder: Many fish have a swim bladder, which helps them control their buoyancy in water.
  • Cold-blooded: Fish are cold-blooded, which means their body temperature is regulated by the temperature of their environment.

Fish Respiration

Fish breathe through gills, which are specialized structures that extract oxygen from water as it flows over them. Water enters the fish’s mouth and passes over the gills, where oxygen is extracted and carbon dioxide is expelled. Some fish, such as lungfish and some catfish, can also breathe air in addition to using their gills.


Fish Classification

Fish are classified into two main groups, Chondrichthyes and Osteichthyes. Chondrichthyes includes sharks, rays, and chimaeras, while Osteichthyes includes bony fish, such as salmon, tuna, and trout.

Class Chondrichthyes Characteristics

Chondrichthyes are cartilaginous fish, meaning their skeletons are made of cartilage rather than bone.

Scales: Chondrichthyes have scales that are modified teeth, called dermal denticles.

Skeleton: As mentioned, their skeleton is made of cartilage instead of bone.

Teeth: Chondrichthyes have multiple rows of sharp teeth that are continuously replaced throughout their lifetime.

Examples of Chondrichthyes

Examples of Chondrichthyes include sharks, rays, and chimaeras.

Class Osteichthyes Characteristics

Osteichthyes are bony fish, meaning their skeletons are made of bone.

Scales: Osteichthyes have scales that are made of bone or enamel.

Skeleton: As mentioned, their skeleton is made of bone.

Swim bladder: Most Osteichthyes have a swim bladder, which helps them control their buoyancy in water.

Examples of Osteichthyes

Examples of Osteichthyes include salmon, trout, tuna, and many other types of bony fish.

Chondrichthyes vs Osteichthyes

One key difference between Chondrichthyes and Osteichthyes is their skeletal composition. Chondrichthyes have a cartilaginous skeleton, while Osteichthyes have a bony skeleton. Additionally, Chondrichthyes have multiple rows of sharp teeth that are continuously replaced throughout their lifetime, while Osteichthyes generally have a single set of teeth that are not replaced. Finally, Chondrichthyes tend to have a more streamlined body shape and are better suited for fast swimming, while Osteichthyes have a more diverse range of body shapes and tend to occupy a wider variety of aquatic environments.

Table comparing Chondrichthyes (cartilaginous fishes) and Osteichthyes (bony fishes)


Amphibians are cold-blooded vertebrates that have smooth, moist skin and undergo a metamorphosis from water-breathing larvae to air-breathing adults. They are found in both aquatic and terrestrial habitats and typically lay their eggs in water. Amphibians are characterized by their ability to breathe through their skin, their webbed feet, and their dual life stages. Examples of amphibians include frogs, toads, salamanders, and newts.


Amphibians are a diverse group of cold-blooded animals that spend part of their lives in water and part on land. They are known for their unique ability to breathe through their skin, which is why they are often referred to as the “canaries of the ecosystem” because they are extremely sensitive to changes in their environment.

Amphibians examples

Frogs, toads, salamanders, newts, and caecilians are all examples of amphibians. These animals come in a variety of sizes, colors, and shapes. Some are small enough to fit on the tip of your finger, while others can grow up to several feet long.

Characteristics of amphibians

One of the most distinctive characteristics of amphibians is their skin, which is thin, smooth, and moist. This allows them to absorb oxygen and moisture through their skin, making them well-suited to life in both aquatic and terrestrial environments. Amphibians also have a three-chambered heart, which is less efficient than the four-chambered heart of mammals and birds, but allows them to adapt to their environment by changing the way they breathe and circulate blood.

Are Turtles amphibians?

They are not actually members of this group. Turtles are reptiles, which are a separate group of cold-blooded animals that are characterized by their scaly skin and the ability to lay eggs on land. Unlike amphibians, turtles have lungs for breathing, and their eggs have hard shells to protect them from drying out on land.

Amphibians vs reptiles

When comparing amphibians to reptiles, there are a few key differences to note. Amphibians typically have smooth, moist skin, while reptiles have dry, scaly skin. Amphibians also have a three-chambered heart, while reptiles have a four-chambered heart. Additionally, amphibians go through metamorphosis during their development, while reptiles do not.

Differences between Amphibians and Reptiles

How do amphibians breathe?

So how do amphibians breathe? As mentioned earlier, they can absorb oxygen and moisture through their skin, which is why they need to keep their skin moist. They also have lungs, which they use primarily when on land or when they need to breathe air more efficiently. Some amphibians also have gills, which they use when they are in the water. This unique combination of breathing methods makes amphibians highly adaptable to their environment, and allows them to thrive in a wide range of habitats.


Reptiles are cold-blooded vertebrates that have dry, scaly skin and are adapted to living on land. They have lungs for breathing and lay their eggs on land. Reptiles are characterized by their ability to regulate their body temperature through behavior and their adaptations for life on land, such as their clawed feet and thick, scaly skin. Crocodiles, lizards, turtles, and snakes are all examples of reptiles.

Having scaly skin and the capacity to lay eggs on land identify reptiles as a distinct group of cold-blooded creatures. They are well-adapted to life in a variety of environments, from deserts to forests to oceans. Let’s explore some of the key characteristics of reptiles and the different types of reptiles that exist.

Characteristics of Reptiles

  • Scaly skin: Reptiles have dry, scaly skin that helps to protect them from moisture loss and predators.
  • Cold-blooded: Reptiles are ectothermic, which means they rely on external sources of heat to regulate their body temperature.
  • Lungs: Unlike amphibians, which can breathe through their skin, reptiles have lungs for breathing air.
  • Three-chambered heart: Most reptiles have a three-chambered heart, which is less efficient than the four-chambered heart of mammals and birds.
  • Eggs with soft or hard shells: Reptiles lay eggs on land, with some species having soft-shelled eggs and others having hard-shelled eggs.

Characteristics and examples of Reptiles

Types of Reptiles

  • Snakes: These legless reptiles are known for their elongated bodies and unique method of movement.
  • Lizards: Lizards have four legs and are found in a wide range of habitats, from deserts to rainforests.
  • Turtles and Tortoises: These reptiles are characterized by their hard, protective shells.
  • Crocodilians: This group includes crocodiles, alligators, and caimans, which are large, carnivorous reptiles found near water.
  • Tuataras: These are rare reptiles that are native to New Zealand and are considered living fossils, as they have remained relatively unchanged for millions of years.

Underground Reptiles

Underground reptiles refer to reptilian species that inhabit underground environments. These reptiles have evolved unique adaptations to survive in the subterranean environment, such as loss of eyesight or highly sensitive senses of smell and hearing. Some examples of underground reptiles include blind snakes, worm lizards, and burrowing turtles.

Are Snakes Vertebrates?

Yes, snakes are vertebrates. Vertebrates are animals that possess a backbone or spinal column, and snakes have a highly modified vertebral column that enables them to move in a serpentine motion. Snakes belong to the class Reptilia, which includes other animals such as turtles, crocodiles, and lizards.

Are Birds Reptiles?

Birds are not reptiles because they have several distinct characteristics that set them apart from reptiles. Although birds and reptiles share some features, such as laying eggs, and having scales, there are significant differences between the two groups.

  • Feathers: Birds have feathers, which are unique to birds and are not found in any other group of animals, including reptiles.
  • Wings: Birds have wings that are specially adapted for flight, whereas reptiles do not have wings or have modified limbs that allow for gliding or swimming.
  • Beaks: Birds have beaks or bills that are adapted for their specific diet, whereas reptiles have jaws with teeth.
  • Skeleton: The skeleton of birds is highly modified for flight and has several unique features, including fused bones and air sacs, that are not present in reptiles.
  • Warm-bloodedness: Although birds and reptiles are both vertebrates, birds are warm-blooded, which means they can regulate their body temperature internally. In contrast, reptiles are cold-blooded and rely on external sources of heat to regulate their body temperature.
  • Behavior: Birds exhibit complex social behaviors, including the formation of long-term pair bonds, caring for young, and vocal communication, whereas reptiles are generally solitary and do not exhibit these types of behaviors.

Are Turtles Reptiles?

Yes, turtles are reptiles. Turtles belong to the class Reptilia and share many of the same characteristics as other reptiles, such as having scales and laying eggs. Turtles also have a unique adaptation of a bony shell that protects their body and limbs, which is made up of modified ribs, vertebrae, and dermal bone.

Are Dinosaurs Reptiles?

Yes, dinosaurs were reptiles. Dinosaurs belong to the same class as modern-day reptiles, Reptilia, and share many of the same traits and characteristics. Dinosaurs were a highly diverse group of animals that lived during the Mesozoic Era, and they ranged in size from small, bird-like creatures to massive, long-necked sauropods. While dinosaurs are no longer present on Earth, their descendants can be seen in modern-day birds.

Birds (Aves)

Birds are warm-blooded vertebrates that have feathers, beaks, and wings. They are adapted to living in the air and have a lightweight skeletal system and powerful muscles that enable them to fly. Birds lay eggs, and some species are capable of complex social behaviors and communication. Birds are characterized by their adaptations for flight, their feathered bodies, and their high metabolic rate. Examples of birds include eagles, owls, parrots, and penguins.

Class Aves, also known as birds, are a diverse group of warm-blooded vertebrates that have a unique set of adaptations for aerial life. There are over 10,000 species of birds, and they can be found in almost every habitat on Earth. Here are some of the key characteristics and examples of birds:

Class Aves characteristics and examples

Feathers: One of the most defining characteristics of birds is their feathers, which provide insulation, help with flight, and are often used for display purposes.

Beaks: Birds have beaks instead of teeth, which vary in shape and size depending on the bird’s diet and lifestyle.

Lightweight skeleton: To make flight easier, birds have a lightweight skeleton that is strengthened by air sacs and fused bones.

Wings: Birds have wings that are modified forelimbs, allowing them to fly or glide through the air.

Advanced respiratory system: Birds have a highly efficient respiratory system that enables them to extract oxygen from the air and expel carbon dioxide quickly.

Endothermic metabolism: Birds are warm-blooded and have a high metabolism that helps them maintain a stable body temperature.

Aves characteristics and examples

Class Aves examples

Bald Eagle – a large bird of prey found in North America, known for its distinctive white head.

Penguin – a flightless bird that is adapted to life in the water, found in the Southern Hemisphere.

Hummingbird – a small bird known for its ability to hover in mid-air and drink nectar from flowers.

Ostrich – the largest living bird, native to Africa and capable of reaching speeds of up to 45 miles per hour.

Albatross – a large seabird that can fly for hours without flapping its wings, found in the Southern Ocean.

Bird’s adaptations for aerial life

Birds have evolved a wide range of adaptations that enable them to live and thrive in the air. These adaptations have been refined over millions of years of evolution and have led to the development of some of the most efficient and agile flying creatures on the planet. Here are some of the key adaptations that birds have developed for aerial life.


The most obvious adaptation that birds have for aerial life is their wings. Birds’ wings are specially designed for flight, with lightweight, hollow bones that provide strength without adding extra weight. The feathers that cover the wings and body are also adapted for flight, providing lift and helping to control the bird’s speed and direction.


In addition to their role in flight, feathers also provide insulation and waterproofing for birds. Feathers are lightweight and strong, allowing birds to fly with minimal energy expenditure. They are also arranged in a way that allows for maximum efficiency in flight.

Aerodynamic body shape

Birds’ bodies are streamlined and aerodynamic, which reduces drag and helps them fly more efficiently. Their bodies are also lightweight, which reduces the amount of energy required for flight.

Muscular system

The muscles of a bird’s chest are particularly well-developed, providing the power required for flapping its wings. Birds have a unique respiratory system that allows them to take in oxygen more efficiently than other animals, which helps to power their muscles during flight.

Strong bones

Birds have a unique bone structure that provides strength and support for their wings while still being lightweight. Their bones are hollow and filled with air sacs, which reduces weight without compromising strength.


Mammals are warm-blooded vertebrates that have fur or hair, mammary glands, and specialized teeth. They are found in a wide range of habitats, from deserts to forests, and from the depths of the ocean to the tops of mountains. Mammals give birth to live young and nurse them with milk. They are characterized by their adaptations for life on land, such as their limbs and specialized teeth, and their ability to regulate their body temperature. Examples of mammals include humans, cats, dogs, whales, and elephants.

What are mammals?

List of Mammals

Mammals are a diverse group of animals that are found in almost every corner of the world. They are warm-blooded, have hair or fur, and produce milk to feed their young.

Here are some examples of different types of mammals:

  • Primates (e.g., humans, apes, monkeys)
  • Carnivores (e.g., lions, tigers, bears, wolves)
  • Herbivores (e.g., cows, horses, deer, elephants)
  • Rodents (e.g., mice, rats, squirrels)
  • Marsupials (e.g., kangaroos, opossums)
  • Bats
  • Whales and dolphins
  • Seals and sea lions
  • Giraffes
  • Anteaters

Characteristics of Mammals

  • Hair or fur: All mammals have hair or fur, which helps to keep them warm and protect their skin.
  • Mammary glands: Female mammals produce milk to feed their young, which is produced by specialized glands called mammary glands.
  • Warm-blooded: Mammals are warm-blooded, which means that they can regulate their body temperature internally.
  • Three middle ear bones: Mammals have three middle ear bones (the malleus, incus, and stapes), which allow them to hear a wide range of sounds.
  • Diaphragm: Most mammals have a diaphragm, which is a muscle that separates the chest and abdominal cavities and helps with breathing.
  • Teeth: Mammals have different types of teeth (incisors, canines, premolars, and molars) that are adapted for different diets.

Characteristics and examples of Mammals

Do Mammals Lay Eggs?

There are a few notable exceptions to the rule that most mammals give birth to newborns. The monotremes (e.g., platypus, echidnas) are a group of mammals that lay eggs instead of giving birth to live young. They are found in Australia and New Guinea and are considered to be some of the most primitive mammals. Other than monotremes, all other mammals give birth to live young.

Sea Mammals

Sea mammals are a group of mammals that have adapted to life in the water. They include a variety of animals, such as whales, dolphins, seals, sea lions, and manatees. Some characteristics that are common to sea mammals include a streamlined body shape, the ability to hold their breath for long periods of time, and a layer of blubber that helps to keep them warm in cold water.

Whales and dolphins are known for their intelligence and social behavior, while seals and sea lions are known for their agility on land and in the water. Manatees are gentle herbivores that live in shallow waters and are threatened by habitat loss and boat strikes.

Venomous Mammals

Venomous mammals are rare, but they do exist. Venom is a toxin that is produced by certain animals and is used for defense, hunting, or competition. Some examples of venomous mammals include:

  • Platypus: The male platypus has spurs on its hind legs that can deliver a venomous sting. The venom is not lethal to humans, but it can cause pain, swelling, and other symptoms.
  • Solenodon: The solenodon is a nocturnal mammal that is found in the Caribbean. It has venomous saliva that it uses to subdue its prey, which includes insects, small reptiles, and rodents.
  • Slow Loris: The slow loris is a small primate that is found in Southeast Asia. It has a gland in its elbow that produces a venomous secretion, which it can deliver to predators or prey through its teeth.
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Anuradhika Lakmali

Anuradhika Lakmali is a co-founder of Science A Plus learning network. She is working as a government teacher and has interest in chemistry, biology, phisics and self development.