Class Aves – Birds
Birds are among the most interesting and the majority of a widely known group of animals.
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- Birds share with mammals the highest development in the animal kingdom.
- It is believed that both birds and mammals have evolved from reptiles along different lines.
- The earliest known bird fossil is that of archaeopteryx, two species of which have been found in rocks of the Jurassic period of Earth’s history.
- The fossil reveals that archaeopteryx was about the size of a crow with a skull similar to that of present-day birds.
- It had bony teeth in the jaw socket, unlike modern birds which do not have teeth.
- Jaws extended into a beak and there was a long tail. Each wing had 3 claws. Except plumes, these birds showed similarity to the dinosaurs (huge reptiles of the past).
- Many fossils of birds from later periods of earth’s history have likewise been discovered that had teeth.
- The above evidence suggests that birds evolved from reptilian forefathers.
- The archaeopteryx and others had characteristics of both reptiles and birds and for that reason form a connecting link between the two unique groups.
Classification of Birds
The class Aves is divided into 2 categories:
Archaeornithes
This class of birds is extinct. They had a toothed beak with a long lizard-like tail.
Example: Archaeopteryx
Neornithes
These consist of extant in addition to extinct birds. They have no teeth and a short tail.
Example: Penguin, Grey Heron, Kingfisher, Duck, and so on.
General Characteristics of Aves
- Birds are warm-blooded, bipedal, feather clawed vertebrates.
- Birds body is divisible into head, neck, Trunk, and Tail.
- In Birds Forelimbs are modified into wings. Forelimb bears 3 claws less digit’s wings bear plumes. They are useful for flying.
- In Birds Skull is monocondylic.
- Modern birds have no teeth. Since birds do not have teeth, they have actually developed a thick muscular structure (Gizzard) in the stomach which is utilized for crushing food.
- In Birds bones are spongy and pneumatic. They are light in weight and strong. They are use full for flying.
- In Birds Posterior caudal vertebrae has a united arm a pygostyle. It acts as a rudder. During the flying, it helps to change the direction of motion.
- The sternum is broad. It shows a keel. This keel works for the attachment of muscles.
- The clavicle and inter clavicle join to form V-shaped furcula. This will keep the wings away.
- Birds Eyes are well developed. They have monocular vision. In the eye comb plate or pecten is present. It protects the retina from sunlight. It also increases the vision.
- Birds brain is well developed. Cerebral hemispheres and cerebellum are present,12 pairs of cranial nerves exist.
- Sexes are different – Sexual dimorphism is clearly displayed.
The circulatory system has a 4-chambered heart and there is only the right aorta that curves to the right side and then bends backward.
- The lungs have extensions known as air-sacs which extend into the bones also.
- The organ of voice is called syrinx, it is situated at the lower end of the trachea near the origin of the two bronchi.
- Some birds have secondarily lost the power of flight and are called running birds e.g., Ostrich, Kiwi, and so on.
Adaptations of Birds
- Streamline Body:
It is designed to offer minimum resistance to the wind.
- Plumes:
They provide the passage for air and reduce friction to the minimum. They likewise prevent loss of heat and help to preserve a consistent temperature.
- Endoskeleton:
The majority of bones are pneumatic and filled with air instead of bone marrow. It makes the body light. Most of the bones are strongly merged together, which assist in flight.
- Warm-Bloodedness (Endothermy):
Birds are warm-blooded animals that are required for flight.
- Absence of Urinary Bladder:
Other than Rhea, the urinary bladder is absent in birds. Excreta are passed out at once. This assists in minimizing the weight of the body.
- Single Ovary:
The presence of a single functional ovary on the left side in the female bird also results in a decrease in weight which is so vital for flight.
MCQs on Class Aves
- What class do birds belong to?
- A. Mammals
- B. Reptiles
- C. Aves
- D. Amphibians
Answer: C
- Which period in Earth’s history is associated with the earliest known bird fossil, Archaeopteryx?
- A. Cretaceous
- B. Jurassic
- C. Triassic
- D. Devonian
Answer: B
- What feature did Archaeopteryx share with modern-day birds?
- A. Teeth
- B. Fur
- C. Scales
- D. Claws
Answer: A
- Which category of birds had a toothed beak and a long lizard-like tail?
- A. Neornithes
- B. Flying birds
- C. Archaeornithes
- D. Raptors
Answer: C
- What is the classification of birds with no teeth and a short tail, such as Penguin and Duck?
- A. Archaeopteryx
- B. Neornithes
- C. Raptors
- D. Flying birds
Answer: B
- What are the general characteristics of Aves?
- A. Cold-blooded, bipedal, featherless vertebrates
- B. Warm-blooded, quadrupedal, feathered vertebrates
- C. Warm-blooded, bipedal, feathered vertebrates
- D. Cold-blooded, quadrupedal, feathered vertebrates
Answer: C
- What is the modified form of forelimbs in birds?
- A. Claws
- B. Wings
- C. Fins
- D. Paws
Answer: B
- What is the purpose of the gizzard in birds?
- A. Sight
- B. Hearing
- C. Smelling
- D. Crushing food
Answer: D
- What structure in birds acts as a rudder during flight?
- A. Beak
- B. Pygostyle
- C. Furcula
- D. Keel
Answer: B
- What is the organ of voice in birds called?
- A. Larynx
- B. Syrinx
- C. Trachea
- D. Bronchi
Answer: B
- What is the role of the pecten in birds’ eyes?
- A. Enhances smell
- B. Protects the retina from sunlight
- C. Improves hearing
- D. Provides taste
Answer: B
- How many pairs of cranial nerves exist in the well-developed brain of birds?
- A. 6
- B. 8
- C. 10
- D. 12
Answer: D
- What is the circulatory system of birds characterized by?
- A. 2-chambered heart
- B. 3-chambered heart
- C. 4-chambered heart
- D. 5-chambered heart
Answer: C
- What extensions do the lungs of birds have?
- A. Alveoli
- B. Bronchi
- C. Air-sacs
- D. Capillaries
Answer: C
- Which class of birds is characterized by running birds that have lost the power of flight?
- A. Archaeopteryx
- B. Neornithes
- C. Raptors
- D. Flightless birds
Answer: D
- What adaptation in birds provides minimum resistance to the wind?
- A. Heavy bones
- B. Streamlined body
- C. Absence of feathers
- D. Long tail
Answer: B
- What purpose do plumes serve in birds?
- A. Increase friction
- B. Prevent loss of heat
- C. Reduce air resistance
- D. Enhance visibility
Answer: C
- Why are most bones in birds pneumatic and filled with air?
- A. For buoyancy
- B. For camouflage
- C. For protection
- D. For flight efficiency
Answer: D
- What is the term for warm-bloodedness in birds?
- A. Ectothermy
- B. Endothermy
- C. Thermoregulation
- D. Homeothermy
Answer: B
- What is absent in birds except for Rhea, aiding in minimizing body weight?
- A. Wings
- B. Beak
- C. Urinary bladder
- D. Feathers
Answer: C
- What contributes to the decrease in weight in female birds, crucial for flight?
- A. Single functional ovary
- B. Strong bones
- C. Large wings
- D. Thick plumage
Answer: A
- What class of birds has an extinct category called Archaeornithes?
- A. Neornithes
- B. Raptors
- C. Archaeopteryx
- D. Both A and C
Answer: D
- What is the modified form of the sternum in birds, aiding in muscle attachment for flight?
- A. Keel
- B. Ridge
- C. Crest
- D. Spur
Answer: A
- Which part of the bird’s body acts as a V-shaped structure keeping the wings away?
- A. Beak
- B. Pygostyle
- C. Furcula
- D. Tail
Answer: C
- What is the purpose of the syrinx in birds?
- A. Respiration
- B. Digestion
- C. Reproduction
- D. Vocalization
Answer: D
FAQs – Class Aves – Birds
- Q: What is the significance of the Archaeopteryx fossil in the study of birds?
- A: The Archaeopteryx fossil is crucial as it represents an early bird species, providing a connecting link between reptiles and modern birds.
- Q: How did the early birds, like Archaeopteryx, differ from modern birds?
- A: Unlike modern birds, early birds such as Archaeopteryx had bony teeth in the jaw socket and a long lizard-like tail.
- Q: What categories are birds classified into in the class Aves?
- A: Birds in the class Aves are classified into two categories: Archaeornithes (extinct) and Neornithes (extant and extinct).
- Q: Can you provide examples of birds belonging to the Archaeornithes category?
- A: Archaeopteryx is an example of a bird belonging to the Archaeornithes category.
- Q: What are some general characteristics of birds in the class Aves?
- A: Birds in the class Aves are warm-blooded, bipedal, and have feathered claws. Their bodies are divisible into head, neck, trunk, and tail.
- Q: How have the forelimbs of birds been modified for flight?
- A: The forelimbs of birds have been modified into wings, each bearing three claws. The wings also have feathers that are useful for flying.
- Q: Why do modern birds lack teeth?
- A: Modern birds lack teeth, and instead, they have a thick muscular structure (gizzard) in the stomach for crushing and processing food.
- Q: What is the significance of the pneumatic and spongy bones in birds?
- A: Pneumatic and spongy bones in birds are lightweight and strong, contributing to their ability to fly.
- Q: What purpose does the pygostyle serve in the posterior caudal vertebrae of birds?
- A: The pygostyle acts as a rudder during flight, helping to change the direction of motion.
- Q: How is the vision of birds adapted to their environment?
- A: Birds have well-developed eyes with monocular vision. The comb plate or pecten protects the retina from sunlight and enhances vision.
- Q: What is the structure responsible for the voice in birds, and where is it located?
- A: The organ of voice in birds is called syrinx, situated at the lower end of the trachea near the origin of the two bronchi.
- Q: Do all birds have the power of flight, or are there exceptions?
- A: Some birds, like the Ostrich and Kiwi, have secondarily lost the power of flight and are referred to as running birds.
- Q: What adaptations do birds have for flight?
- A: Birds have a streamlined body for minimal wind resistance, plumes for air passage and temperature regulation, and pneumatic endoskeleton for lightweight.
- Q: Why is warm-bloodedness (endothermy) essential for birds?
- A: Warm-bloodedness is crucial for flight as it helps maintain a constant body temperature, which is necessary for metabolic activities during flight.
- Q: What is unique about the circulatory system of birds?
- A: Birds have a 4-chambered heart with only the right aorta curving to the right side and then bending backward.
- Q: Why is the urinary bladder absent in most birds?
- A: The urinary bladder is absent in most birds, except for Rhea, to reduce body weight by passing out excreta promptly.
- Q: How does the presence of a single ovary contribute to flight in female birds?
- A: The presence of a single functional ovary on the left side in female birds reduces weight, which is vital for flight.
Summary
The Class Aves tutorial provides a comprehensive exploration of birds, highlighting their evolutionary history, classification, general characteristics, and unique adaptations. Birds, considered one of the most fascinating groups of animals, share a common ancestry with mammals, both evolving from reptiles along distinct lines. The tutorial introduces the earliest bird fossil, archaeopteryx, serving as a crucial link between reptiles and modern birds.
The classification of birds into Archaeornithes (extinct) and Neornithes (extant and extinct) is detailed, featuring examples such as Archaeopteryx, Penguins, Grey Heron, and more. The general characteristics of birds, including warm-bloodedness, bipedalism, and feathered claws, are explored. The tutorial delves into the modifications of forelimbs into wings, the absence of teeth in modern birds, and the unique skeletal features contributing to flight.
The circulatory system, respiratory adaptations, and the presence of a syrinx for vocalization are outlined. Notably, the tutorial addresses adaptations essential for flight, such as the streamlined body, plumes for air passage, and a pneumatic endoskeleton. The importance of warm-bloodedness for flight, the absence of a urinary bladder (except in Rhea), and the presence of a single ovary in female birds are discussed as key aspects of bird biology.
In summary, the tutorial provides a comprehensive understanding of the avian world, offering insights into their evolution, classification, and remarkable adaptations that enable their diverse lifestyles.