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Vertebrata – Definition, Classification, Characteristics, Features

Last Updated : 17 Aug, 2022
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Diversity in living organisms can be found all over the world. The earth’s warm and humid regions are highly diverse and are known as the region of mega biodiversity. More than half of the world’s biodiversity is concentrated in 12 countries. One of them is India. Our planet is endowed with a plethora of living organisms that differ in size, shape, habitat, nutrition, reproduction, and many other ways. These animals of Kingdom Animale are classified into different orders and classes based on their physical characteristics and habitat. Animals that live in various environments, such as water, land, deserts, forests, grasslands, ice land and water, and ice to deserts, forests, and grasslands. All of these organisms are made up of what are known as cells.


  • More than 500 million years ago, the earliest vertebrates resembled hagfish.
  • Other classes of fish evolved traits such as a complete vertebral column, jaws, and a bony endoskeleton as they evolved.
  • Amphibians were the first tetrapod vertebrates to live on land, as well as the first vertebrates to evolve.
  • The first amniotic vertebrates were reptiles.
  • Endothermy, or the ability to regulate body temperature from the inside, evolved in mammals and birds, both of which descended from reptile-like ancestors.


Vertebrates are species that have a backbone or vertebrae. Reptiles, humans, birds, fish, mammals, and amphibians are examples of vertebrate animals. Craniata is another name for these. Vertebrates are animal species that belong to the Subphylum Vertebrata, which means chordates with a backbone. Animalia is the vertebrate kingdom, which includes the subphylum Deuterostomia and the phylum Chordata. Olfactories is its clade, or monophyletic group, with Agnatha and Gnathostomata as infraphylums.

Osseo Batch is a synonym or alternative name for vertebrates. The size of a living vertebrate animal ranges from the frog Paedophryne amanuensis [7.7 millimeters or 0.30 inch] to the blue whale [up to 30 meters or 108 feet]. Among the vertebrates are:

  • Fish with no jaws (Lampreys and Hagfish)
  • Jawed vertebrates [cartilaginous fish such as ratfish and shark; bony vertebrates such as ray fins and lobe fins (tetrapods and lungfish)].

These species are called vertebrates because they have vertebrae or backbones. Here are some examples of vertebrates:

Amphibians and birds (Aves) (Amphibia) Mammals (Reptilia) Reptiles (Reptilia) Fishes (Osteichthyes) (Mammalia).

Characteristics of Vertebrates 

  • Jaws can be found in some vertebrates. Jawless species are classified as vertebrates.
  • The notochord eventually becomes a vertebral column, with the vertebrae on the dorsal side.
  • The anatomy of vertebrates is strikingly similar, with a vertebral column, gastrointestinal tract, and spinal cord all present.
  • The internal skeleton helps to distribute muscle attachment nodes.
  • The presence of the central nervous system is an important indicator. The anterior nerve tube of the spinal cord expands into the brain.

Classification of vertebrates 

Class Reptilia 

Reptiles’ bodies are covered by scutes or scales, and the epidermal scales can be shed in some cases. There is no external pinna, and the auditory functions are performed by the tympanum. Crocodiles have four-chambered hearts, while reptiles have three-chambered hearts. Reptiles, unlike other vertebrates, have cold-blooded animals. Tortoise, turtle, crocodile, snake, and other examples. 

  • These are terrestrial animals that creep and burrow and have scales on their bodies. The skull has a single condyle.
  • They are cold-blooded animals found in most of the world’s warmer regions.
  • The body is divided into four sections: the head, neck, trunk, and tail. Their skin is rough and dry, with no glands.
  • Few of these shed their skin scales as skin cast. Respiration is accomplished through the use of the lungs.

Class Mammalia 

Mammary glands are present to feed the young. Mammals have functional limbs as well as an external pinna. Fertilization is usually internal in these vertebrates. Mammals have four chambers in their hearts and warm blood. They usually give birth to their offspring, but there are some exceptions, such as Echidna, which reproduce by laying eggs. The habitats of these vertebrates vary. Kangaroo, dolphin, whale, and platypus are some examples.

  • Mammals are warm-blooded creatures that give birth to their young.
  • They are the most common type of animal found in almost all habitats.
  • They have mammary glands, which aid in the production of milk to feed their young. Cervical vertebrae are also found in mammals.
  • The presence of the Neocortex brain region. They are heterodont, which means they have different types of teeth. The skull has two condyles.
  • Their skin contains oil glands (sebaceous glands) as well as sweat glands (sudoriferous glands).
  • The fur of hair covers the body and aids animals in adapting to their surroundings.

Class Amphibia

This class contains 4000 different species of animals that spend their larval/juvenile stages in water and their adult lives on land. To mate and lay eggs, amphibians must return to the water. Most adults have moist skin, which aids in gas exchange in their small, inefficient lungs. This transitional group consists of frogs, toads, newts, salamanders, and mudpuppies. Amphibian characteristics not found in bony fish include:

  • Limbs with bone girdles that are designed for walking on land.
  • A tongue that can be used for both prey capture and sensory input.
  • A vocalization-adapted larynx.
  • Ears are designed to detect sound waves moving through the thin (in comparison to water) medium of air.
  • Eyelids that aid in keeping the eyes moist.

Class Aves (birds) 

The Aves are members of the animal kingdom’s phylum Chordata. It has approximately 9,000 species. Aves have the ability to fly. The Aves class includes all birds. They exhibit courtship, parental care, nest construction, and territorial behavior. Birds are dinosaurs from a biological standpoint (more aptly called avian dinosaurs). This group of organisms is distinguished by feathers, toothless beaks, and a rapid metabolic rate. Members of the Aves class also lay hard-shelled eggs. 

  • Birds are warm-blooded creatures. They have excellent vision. Their forelimbs have been transformed into wings. They don’t have any teeth.
  • They have well-developed flight muscles, which aid in flight. The lower and upper jaws have been modified to form a beak.
  • Their hind limbs have evolved to allow them to walk, hop, perch, grasp, wade, and swim. By allowing air to pass through, friction is reduced.
  • Their spindle-shaped body reduces wind resistance. The feathers prevent heat loss and reduce airflow. Their legs are covered in epidermal scales.
  • The endoskeleton is made up of bony structures with long hollow bones filled with air cavities. referred to as pneumatic bones. Except for the oil gland, there are no skin glands.

Class Osteichthyes 

It is the largest vertebrate class and the class of bony fish, with skeletons that have bones rather than cartilages like sharks. The class Osteichthyes includes approximately 20,000 species of bony fish found in both saltwater and freshwater. There are two types of fish in this class: lobe-finned (Sarcopterygii) and ray-finned (Sarcopterygii) (Actinopterygii). A bony skeleton is present in bony fish. The majority of species in this class have ray fins, which are supported by thin, bony rays. A few fishes have lobe-finned fins and are thought to be related to amphibians’ ancestors.

Class Agnatha  

These are primitive jawless fishes with circular mouths and small sharpened teeth for feeding and holding the type of fish. The vast majority of them are scavengers and parasites. The Cyclostomata are a degenerate and modified offshoot of the primitive vertebrate stalk. Because of their circular mouth, they are known as Cyclostomata. They feed on fish in their adult stage and are parasitic. They are morphologically similar to eels. They are the only living vertebrates without true jaws, hence the name Agnatha. Cyclostomata is found in hagfishes and lampreys. Lampreys hatch in freshwater and spend the majority of their lives there. Although some lampreys migrate to the sea, they must return to freshwater to reproduce. Lampreys have a sucker-like mouth with no jaw.

Class Chondrichthyes 

  • The cartilaginous skeleton, as the name implies, distinguishes this class. Members include sharks, rays, skates, and sawfish.
  • Some sharks, such as the massive Greenland shark, can live for hundreds of years. A specimen tagged in 2016 was discovered to be at least 273 years old.
  • These are true jawed vertebrates with breathing, excretory, and circulatory systems.
  • Poikilotherms are organisms that are unable to regulate their own body temperature. 
  • This category contains fish with scales all over their bodies. These vertebrates are oviparous, and they breathe only through their gills. Fish have two-chambered hearts and skeletons that are entirely made of cartilage.

General Features 

  • The skull is found in vertebrates. This safeguards the sensitive, well-developed brain.
  • Vertebra/backbone: The backbone is made up of a series of small bones called vertebrae. The spinal cord is housed in the vertebral column.
  • Endoskeleton: The endoskeleton of vertebrates is well developed. This is an internal skeleton that gives structure to the body of a vertebrate.
  • Vertebrates have two pairs of appendages, such as wings, fins, or limbs. These appendages are found in pairs on the body of vertebrates.
  • Bilateral Symmetry: These organisms are symmetrical on both sides. This means that vertebrates have mirror images of their right and left halves.

External Features

  • The vertebrate’s specialization for active capture of larger prey is evident in both the structure of the mouth and the relatively simple structure of the pharynx, with its strong gill development.
  • The evolution of the chordate notochord, dorsal nerve tube, and pharyngeal slits suggests improved swimming ability and, most likely, greater ability to capture prey.
  • Swimming adaptations are also numerous, involving variations in body form as well as medial and lateral fins.
  • Feeding specialization is seen again in the two basic groups of vertebrates, agnathans, and gnathostomes.

Internal Features

  • The skeletal system’s exoskeletal and endoskeletal divisions provide support and protection. When present, the exoskeleton is primarily protective but also serves as tooth support in the mouth region.
  • The endoskeleton protects the brain and spinal cord and primarily aids in trunk and tail locomotion. The endoskeleton begins as cartilage and can either remain that way or develop into bone.
  • The cartilaginous endoskeleton of a shark or chimaerid is typically calcified to make it stiffer and stronger.
  • Bone is distinct but highly variable; some types of bone contain cells, while others do not; bone can be laminar, spongy, or arranged in sheathing layers around blood channels.

Nervous system and sense organ 

  • The dorsal position, tubular structure, and epidermal origin of the central nervous system distinguish chordates from hemichordates, though some may see similarities.
  • The sensory structures of chordates are distinct, and they include paired nasal, optic, and otic organs (along with the strongly differentiated head).
  • The nasal vesicle is open to the environment in various ways, and its sensory cells, as chemical receptors, are similar to those found in the taste buds of the mouth.
  • The eye is the most complex organ of the head, and it is formed by a lateral out pocketing of the anterior end of the brain tube. Later on, it develops an epidermal lens.
  • The act of focusing the eye (accommodation) exhibits extensive adaptive variation among vertebrate groups.
  • The otic vesicle develops from a simple sac formed by ectodermal placode invagination. These developmental changes also include innervation changes.
  • Whereas the original structure was primarily an equilibrium adaptation, other functions such as movement awareness and the sensation of prey proximity developed.
  • The lateral-line system of canals and sensory organs is a distinctive feature of vertebrates. This system’s components can be found on both the head and the body.
  • This system is related to the ear and may have served a similar function in the past. In terrestrial vertebrate forms, this system is lost.

Frequently Asked Questions

Question 1: Explain about class Mammalia type of vertebrates. 


Mammals are warm-blooded and have a four-chambered heart. They give birth to their offspring directly, with the exception of the Echidna, which reproduces by laying eggs. These vertebrates have internal fertilization, and they have mammary glands to feed their young.

Question 2: Mention the classification of vertebrates based on anatomical and physiological characteristics. 


Vertebrates are divided into seven groups based on anatomical and physiological characteristics. These are their names:

  • Chondrichthyes class
  • Mammalia class
  • Aves Class
  • Reptilia class
  • Agnatha class 
  • Osteichthyes class
  • Amphibia class

Question 3: Explain some characteristics of amphibia? 


  • The kidneys are mesonephric in shape. 
  • They have ten cranial nerve pairs.
  • Water is where breeding takes place. Males do not have copulatory organs.
  • A metamorphosis is a form of indirect development.
  • The sexes are distinct, and fertilization is usually done externally. In salamanders, however, fertilization occurs internally
  • For example, frogs and salamanders.

Question 4: What types of vertebrates lay amniotic eggs?


Amniotic eggs are primarily produced by reptiles and birds. Mammals, which are specialized for internal development, also lay amniotic eggs. However, prehistoric mammals laid eggs, as do some modern mammals.

Question 5: How many different kinds of mammals are there? 


Mammalia is the animal kingdom’s largest class. Based on reproduction, they are classified into three subclasses::

  • Eutheria
  • Metatheria
  • Prototheria

Question 6: What is the classification of aves? 


The Aves class is divided into two groups:

  • Archaeornithes-This species of bird is extinct. They possessed a toothed beak and a long lizard-like tail. For instance, Archaeopteryx
  • Neornithes-These includes both living and extinct birds. They lack teeth and have a short tail. For example, a penguin, a grey heron, a kingfisher, a duck, and so on.

Question 7: When did vertebrates emerge? 


It is thought that the first vertebrates evolved 525 million years ago. Myllokunmingia is thought to be the first vertebrate. Other evidence, however, points to Pikaia gracilens as the first vertebrate and the ancestor of all modern vertebrates. 

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