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Check Phylum Chordata Superclass Tetrapoda notes for NEET 2019 here! Phylum

Chordata is important sections in the Animal Kingdom unit which are mostly asked every

year in NEET, AIIMS, and JIPMER exams. Go through this article to know about Class

Amphibia, Reptilia, Aves, and Mammalia. Let's start with the introduction of Animal

Kingdom and its classification.

Animal Kingdom Superclass Tetrapoda

Introduction

The word “Tetrapoda” was derived from a Greek word which meant “four legs”. Some of

the major groups that fall under Tetrapoda include Amphibians, Reptiles (embraces birds

and dinosaurs also), and mammals. All terrestrial vertebrates, such as lions, hawks,

turtles, and frogs belong to class Tetrapods. Other than terrestrial animals, Tetrapods also

include those animals which have returned their life in water, such as sea snakes, whales,

sea turtles, dolphins, and sea lions. The group also includes extinct animals such as

mosasaurs.

The first vertebrates to truly walk on the land were the early tetrapods. Before the

existence of tetrapods, all vertebrates were confined to aquatic habitats. The conquest of

land by the tetrapods, began in the Paleozoic era which, was around 360 million years

ago. The closest living relatives of tetrapods are the lungfishes.

The key characteristic features of Tetrapods for their classification include the skull and

their four limbs (or if at all they lack four limbs, their ancestors had four limbs. For

example: snakes, caecilians, cetaceans, and so on). The skull is the collection of bones

that surrounds the brain, and it also includes the jaw. The arrangement and the structure

of bones in skull give the name to the major groups of amniote tetrapods. Approximately

30,000 species of tetrapods are reported till date.

Tetrapods may vary greatly in size. The largest living tetrapod reported is the blue whale.

It can grow its length up to 30 meters. Paedophyrine frog is the smallest reported tetrapod,

measuring up to a length of just 8 millimeters.

Habitat of Tetrapods:

Tetrapods inhabit a wide variety of terrestrial habitats which include grasslands,

scrublands, deserts, forests, polar regions, and mountains. While most of the tetrapods

are terrestrial, various groups have evolved to live in aquatic habitats. Tetrapods such as

seals, otters, sea snakes, whales, salamanders, and so on have evolved to depend on

aquatic habitats for some or all phases of their life cycle. Some tetrapods, such as flying

squirrels, bats, and birds have also adopted an aerial or arboreal lifestyle.

Key characteristic features of Tetrapods:

1. They have four limbs (or are descendants of ancestors having four limbs).

2. Their skeleton and muscles are adapted to enable proper support and movement

on land.

3. Cranial bones are adapted to allow their head to stay stable during movement.

4. They possess a layer of dead cells which reduce loss of water across their body

surface.

5. They possess well-developed muscular tongue.

6. They lack internal gills.

7. They possess olfactory organ, which enables them to detect pheromones and play

important role in smell and taste.

8. They possess harderian gland (lubricates eyes) and parathyroid gland (controls

blood calcium level).

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Characteristic features of the four classes of Tetrapoda

Amphibia Reptilia Aves Mammals

Habitat: Both

aquatic and

terrestrial

Habitat: Mostly

terrestrial

Habitat: Feathers

are present for

flying

Habitat: Mostly

terrestrial, although

some can fly and

some are aquatic

Limbs: Two pairs Limbs: If present,

two pairs

Limbs: Modified

forelimbs as wings Limbs: Two pairs

Skin: Moist without

scales

Skin: Dry, cornified

skin with scale

Skin: Dry without

glands Skin: Hairy skin

Respiration:

Through lungs,

gills, or skin

Respiration:

Through lungs

Respiration:

Through lungs

Respiration:

Through lungs

Heart: Three

chambered and cold

blooded

Heart: Three

chambered with

exception of four

chambered

crocodile

Heart: Four

chambered and

warm blooded

Heart: Four

chambered

Oviparous Oviparous Oviparous Oviparous or

Viviparous

Example:

Salamander, Rana

(frog)

Example:

Chameleon,

Crocodile

Example: Ostrich,

Columba

Example: Dog, Blue

whale, Platypus

(Oviparous)

Class 1: Amphibia (General Characteristics, the difference between Frog, Toad,

ichthyophis, Salamander, Seymouria)

General Characteristics

Amphibians do not have a constant body temperature. They take on the temperature of

their surrounding environment. Hence, they are termed as cold-blooded animals. They

possess moist skin that lacks scales, which allows absorption of oxygen and water and at

the same time makes them vulnerable to loss of bodily fluids.

Approximately 6,200 species of living amphibians have been identified till date.

Amphibians are classified into three orders; Frogs and toads, newts and salamanders, and

caecilians. Frogs and toads are adapted for jumping, newts and salamanders can either

walk or swim, and caecilians only live in water or soil. They are the only amphibians with

no legs.

Difference between Frogs, Toads, Ichthyophis, Salamander, Seymouria

Frogs and toads lack tail in their adulthood, which is a distinguishing feature from other

amphibians. Frogs and toads also have longer back legs (modified for jumping) as

compared to other amphibians. Although they are closely related, they differ in various

ways. Frogs spend more time in water while toads spend more time on land. Frogs have

moister, smoother skin than toads and longer hind legs. On the other hand, salamanders

and newts possess tails even in adulthood. They possess long body with shorter legs with

same length adapted for swimming and walking. They possess an unusual characteristic

of regenerating legs after having been lost to predators. Caecilians are closely related to

salamanders. They possess a long, worm-like body with no legs. They evolved from a

tetrapod ancestor, but during the course of evolution they lost their legs. Ichthyophis is

a genus of caecilians. Seymouria is an extinct genus of terrestrial tetrapod found as fossils

in Permian rocks.

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Class 2: Reptilia (General characteristics, Difference between Tortoise, chelone,

chameleon, Hemidactlylus, Hydrophis, Phrynosoma)

General Characteristics

All reptiles are vertebrates (have a backbone) and most of the reptiles lay hard shelled

eggs, while a few give birth to young ones. Reptiles are also cold blooded and they possess

scutes or scales. They are mostly terrestrial and inhabit the warmer region of the world.

They respire through lungs.

Difference between Tortoise, chelone, chameleon, Hemidactlylus, Hydrophis,

Phrynosoma

Tortoise is half terrestrial inhabiting mainly in fresh water and is larger in size. Chelone,

also known as turtles, are aquatic inhabiting mainly in marine and are comparatively

smaller in size. Tortoise does not have paddles and their head show many movements

while turtles have paddles and their head cannot move. Hemidactylus is found in all the

tropical regions of the world. It is a genus of the gecko family. Approximately 90 species

of Hemidactylus has been described. Hydrophis is also known as sea snake. Their tail is

compressed laterally and is adapted to swim in water. It is deadly poisonous.

Phrynosoma are also known as “Horned lizards”. Phrynosoma means toad-bodied and

are characterized by rounded, flattened body with blunt snout. Chameleons are

distinguished by their highly modified, extrudable tongues, and horns on their bows. 203

species of Chameleons are identified till date. They have independently mobile eyes with

stereoscopic vision.

Class 3: Aves (General Characteristics), kiwi, Hummingbird, Short note on birds

are glorified reptiles.

General Characteristics

Aves possess a spindle shaped body having four divisions: head, neck, trunk, and tail.

Their forelimbs are modified to fly. They have an epidermal covering of feathers and leg

scales and possess either beak or bill. They have a well-developed nervous system and a

four-chambered heart. They are warm blooded and sexes are separated.

Kiwi is the only bird that has nostrils at the tip of their beaks. While other birds hunt their

prey by hearing or by sight, Kiwis use their beaky nostrils to sniff food at night. Although

it has wings, it cannot fly. Humming birds are the smallest birds known, belonging to

family Trochilidae. They have the ability to fly.

Birds are often given the title as “Glorified reptiles”. They are given the title as they are

structurally similar to reptiles, although they have features that are adapted to flying, an

advanced feature. Characteristic features of birds are their beaks and feathers. Feathers

have the function of flight, regulation of body temperature, and attraction of their mates.

Class 4: Mammalia (General characteristics), Differences between Prototheria,

Metatheria and Eutheria

General Characteristics

Mammalia are warm blooded, hairy animals that possess mammary glands. They give

birth to young ones and nourish them with milk. Approximately 4,000 species of mammals

have been identified till date. Their skin possesses both sebaceous (oil) glands and

sudoriferous (sweat) glands. Teeth are heterodont (different types) and are developed

twice in their life-time (milk and permanent). All mammals, except a few, possess seven

neck (cervical) vertebrae. They respire through lungs.

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Differences between Prototheria, Metatheria, and Eutheria

Prototheria Metatheria Eutheria

They are also called ‘Egg

laying mammals’.

They are also called as

‘Pouched mammals or

marsupials’.

They are also called as

‘Placental mammals’.

They possess ear without

pinna.

They possess ear with

pinna.

They possess ear with

pinna.

They are oviparous. They are viviparous. They are viviparous.

They lack placenta. They possess small

placenta.

They possess very large

placenta.

Ornithorhynchus, Macropus, Pteropus, and Balaenoptera.

Ornithorhynchus are also called as duck-billed platypus. They inhabit in both aquatic

and terrestrial habitat. They are endothermic and their physical feature shows bilateral

symmetry. They are oviparous and produce young ones in more than one group

(Iteroparous).

Macropus is a marsupial genus belonging to family Macropodidae. They inhabit terrestrial

habitat. They are endothermic and their physical feature shows bilateral symmetry. They

are viviparous and undergo seasonal breeding.

Pteropus is a genus of bats. They are among one of the largest bats in the world. They

are arboreal. They are endothermic and their physical feature shows bilateral symmetry.

They are viviparous and produce young ones in more than one group (Iteroparous).

Balaenoptera is a genus of Balaenopteridae. It consists of eight extant species. It is also

commonly known as blue whales. They inhabit in aquatic environment. They are

endothermic and their physical feature shows bilateral symmetry. They are viviparous and

produce young ones in more than one group (Iteroparous).

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