Vertebrata - Definition, Classification, Characteristics, Features

Vertebrata division in the Animal Kingdom includes animals with a backbone or spinal column. Animals that belong in Vertebrata examples are such as mammals, birds, reptiles, amphibians, and fish. Vertebrata classification is based on various Vertebrata characteristics like body structure, mode of reproduction, and habitat, providing a detailed understanding of the diversity within this group.

In this article, we will cover the Vertebrata - classification, characteristics, examples, evolution, and more in detail.

Vertebrata Meaning

Vertebrates are animals that have a backbone or vertebrae. Vertebrata examples include reptiles, humans, birds, fish, mammals, and amphibians. Vertebrata are also known as craniata because they possess a skull made of cartilage or bone, which is a defining characteristic of this group.

The size of a living vertebrate animal ranges from the frog Paedophryne amanuensis [7.7 millimeters] to the blue whale [108 feet]. In the Animalia kingdom, the vertebrata subphylum includes the subphylum Deuterostomia and the phylum Chordata.

Vertebrata Examples

Vertebrata includes a wide range of animals, each with distinct characteristics:

• Mammals: Animals like humans, elephants, and whales that have fur or hair and produce milk to feed their young.
• Birds: Examples include eagles, sparrows, and penguins, characterized by feathers, beaks, and the ability to lay eggs.
• Reptiles: Such as snakes, lizards, and turtles, which have scaly skin and typically lay eggs on land.
• Amphibians: Frogs, salamanders, and newts, which usually live both in water and on land during different life stages.
• Fish: Including salmon, sharks, and goldfish which live in water, have gills for breathing and are often covered in scales.

Evolution of Vertebrata

The evolution of Vertebrata is given below:

• 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.

Also Read: What is an Endothermic Animal?

Vertebrata Characteristics

The major characteristics are:

• 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 similar, with a vertebral column, gastrointestinal tract, and spinal cord present in all vertebrates.
• The internal skeleton helps to distribute muscle attachment nodes.
• The presence of the central nervous system is an important trait in this group. The anterior nerve tube of the spinal cord expands into the brain.

Also Read: Facts About Skeletal System

Vertebrata Classification

The Vertebrata is classified into the following classes. Let's discuss in detail:

Class Reptilia 

Reptiles' bodies are covered in scutes or scales, and the epidermal scales is shed in some cases. There is no external pinna, and the auditory functions are performed by the tympanum. Crocodiles are an exception in class Reptilia as they have four-chambered hearts instead of characteristic three-chambered hearts.

Reptiles, unlike other vertebrates, are cold-blooded animals.

• 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.
• Some examples of animals belonging to Class Reptilia are Tortoise, turtles, crocodiles and snakes.

Class Mammalia 

• Warm-blooded: Mammals maintain a constant internal body temperature.
• Internal Fertilization: Reproduction typically involves internal fertilization and live birth. (Echidna is an egg-laying exception).
• Four-chambered Heart: Their hearts have four chambers for efficient blood circulation.
• Mammary Glands: They possess mammary glands for producing milk to nourish their young.
• Hair or Fur: Their bodies are covered in hair or fur for insulation and protection.
• Heterodont Teeth: They have different types of teeth specialized for various functions (incisors, canines, molars).
• Neocortex: Their brains have a well-developed neocortex associated with higher cognitive functions.
• Sweat Glands: They have sweat glands that help in temperature regulation.
• Oil Glands: Their skin also contains oil glands for lubrication and waterproofing.
• Diverse Habitats: Mammals occupy a wide range of habitats, from aquatic environments (whales, dolphins) to land (kangaroos) and even aerial environments (bats).

Also Read: Difference Between Cold-Blooded And Warm-Blooded Animals

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 helps 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 help 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 can fly and the Aves class includes all birds. 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.
• They exhibit courtship, parental care, nest construction, and territorial behaviour.
• 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 help 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 

The class Osteichthyes includes approximately 20,000 species of bony fish found in both saltwater and freshwater. It is the largest vertebrate class and the class of bony fish, with skeletons that have bones rather than cartilage like sharks.

• Two main types:
  • Ray-finned fish (Actinopterygii): This group comprises the vast majority of bony fish species. Their fins are supported by thin, bony rays. (Examples: goldfish, salmon, tuna)
  • Lobe-finned fish (Sarcopterygii): This group is less diverse but has historical significance. Their fins are fleshy lobes with internal bones, thought to be a precursor to limbs in amphibians. (Examples: lungfish, coelacanth)
• Gills with bony covers: Bony fish have gills for respiration, protected by bony covers called opercula.
• Swim bladders: Many bony fish possess a swim bladder, a gas-filled internal sac that helps them control buoyancy and stay at a desired depth.
• External fertilization: Reproduction typically involves external fertilization, where eggs are released in water and fertilized by sperm.

Class Agnatha  

The characteristics of class Agatha are:

• Jawless Vertebrates: Agnatha is the only living group of vertebrates without jaws.
• Circular Mouth: They possess a circular mouth for feeding and attachment.
• Feeding Strategies: While some species are parasitic feeders on fish, others are scavengers.
• Examples: Hagfish and lampreys are the two main Agnatha groups.
• Lamprey Lifecycle: Lampreys hatch in freshwater, spend most of their lives there (though some migrate to sea), and return to freshwater for reproduction.
• Sucker-like Mouth: Lampreys have a specialized mouth for attaching to prey, lacking true jaws.

Class Chondrichthyes 

The characteristics of class Chondrichthyes are:

• 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 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 of Vertebrata

The features of Vertebrata are:

• Endoskeleton: Vertebrates have a well-developed internal skeleton for support and structure. This can be cartilaginous or bony.
• Skull: The skull protects the brain.
• Vertebral Column: The backbone, made of vertebrae, contains the spinal cord and provides flexibility.

External Features of Vertebrata

• The vertebrate's specialization for capturing large prey is evident in both the structure of the mouth and the relatively simpler 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 there which involves 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 of Vertebrata

• The endoskeleton protects the brain and spinal cord and primarily helps 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 Organs of Vertebrata

The Vertebrata have a highly developed nervous system and sense organs.

Nervous System of Vertebrata:

• Dorsal Tubular Structure: The central nervous system (CNS) is located on the dorsal side of the body and has a hollow tube-like structure. This distinguishes vertebrates from hemichordates.
• Epidermal Origin: The CNS originates from the ectoderm, the outer embryonic germ layer.
• Spinal Cord: The CNS runs along the back and is protected by the vertebral column. It transmits signals between the brain and the rest of the body.

Sense Organs of Vertebrata

• Paired Sensory Organs: Vertebrates have paired sensory organs for smell (nasal), sight (optic), and balance/hearing (otic). These organs are located on the head, contributing to a well-developed head region.
• Chemical Reception: The nasal organs detect chemicals in the environment, similar to taste buds.
• Complex Eyes: Eyes are the most complex sensory organs, formed from an outgrowth of the brain and a lens derived from the skin. They allow for vision and have varying focusing abilities across different vertebrate groups.
• Inner Ear Development: The inner ear (otic vesicle) originates from a simple sac and becomes more complex with nerve connections. It plays a role in balance and hearing.
• Lateral Line System: This unique system of canals and organs detects water movement and pressure changes, especially important for aquatic vertebrates. It can also be found on the head and body

Conclusion - Vertebrata

Vertebrates, or animals with a backbone, include a diverse range of species. Some Vertebrata examples include mammals, birds, reptiles, amphibians, and fish. These animals are characterized by their well-developed nervous systems, endoskeletons, and complex organ systems. The evolutionary journey of vertebrates has led to significant adaptations that allow them to thrive in various environments. Understanding vertebrates offers insight into the complexity and diversity of life on Earth, highlighting the importance of preserving these remarkable creatures and their habitats.