Check Phylum Chordata Superclass Tetrapoda notes for NEET 2020 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 surround the brain, and it also includes the jaw. The arrangement and the structure of bones in the 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. The 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:
- They have four limbs (or are descendants of ancestors having four limbs).
- Their skeleton and muscles are adapted to enable proper support and movement on land.
- Cranial bones are adapted to allow their head to stay stable during movement.
- They possess a layer of dead cells which reduce the loss of water across their body surface.
- They possess well-developed muscular tongue.
- They lack internal gills.
- They possess an olfactory organ, which enables them to detect pheromones and play an important role in smell and taste.
- They possess harderian gland (lubricates eyes) and parathyroid gland (controls blood calcium level).
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 the 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 a long body with shorter legs with the 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.
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 the lungs.
Difference between Tortoise, Chelone, chameleon, Hemidactlylus, Hydrophis, Phrynosoma
Tortoise is half terrestrial inhabiting mainly in freshwater 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 the sea snake. Their tail is compressed laterally and is adapted to swim in water. It is deadly poisonous. Phrynosoma is also known as “Horned lizards”. Phrynosoma means toad-bodied and is characterized by a rounded, flattened body with a 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. Hummingbirds 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 lifetime (milk and permanent). All mammals, except a few, possess seven necks (cervical) vertebrae. They respire through the lungs.
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 is 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 an 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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