Class Aves and Mammalia

• Class Aves

  Class of vertebrates that comprises the birds' species
• Class Mammalia

  Class of vertebrates that comprises the mammals
• Class Aves is one of the most evolved species in the animal kingdom categorized under vertebrata
• Classes of vertebrates

  • Class Aves
  • Class Mammalia
• Class Aves

  • Aves is a class of vertebrates that comprises the birds' species
  • Birds are bipedal, feathered, and endothermic egg-laying animals
  • Birds are found worldwide, their sizes ranges from 5 cm to 2.75 meter
  • There are about 10,000 living modern bird species in the world that occupy nearly all habitats on Earth
• Classification of Class Aves

  • NEORNITHES - extant as well as birds with no teeth and a short tail (e.g. Penguin, Kingfisher, Duck)
  • ARCHAEORNITHES - extinct and a toothed beak with a long lizard like tail (e.g. Archaeopteryx)
• 21 Characteristic Features of Class Aves

  • The body of the bird is spindle-shaped, and it is covered with different types of unique structures, feathers for the most part
  • Forelimbs are modified as wings for flight, and the posterior hind limbs are adapted for walking, perching, wading, or swimming
  • The birds' bones are fully ossified and pneumatic or hollow inside, which lower the overall weight of the body
  • Uropygial or oil gland is present in the tail region
  • The mouth is wide, and jaws are covered by horny sheaths that form strong beaks
  • The alimentary canal leads to the cloaca. Alimentary canal often contains additional chambers like crop and gizzard
  • Some bird species, such as pigeon, keep stone in the gizzard to effectively crush grains and seeds
  • Birds are adapted to various modes of feeding due to the modified structures of beak: fruit-scooping, seed-crushing, fishtearing, wood-chiseling, nectar-sipping, grain-pickling, etc.
  • The head is small and round with a relatively long, flexible, and movable neck
  • They have no urinary bladder
  • They have a four-chambered heart with two ventricles and two atria
  • They have small, elastic type lung, which is affixed in the dorsal wall of the thorax and give rise to some air-sacs to increase its efficiency
  • The kidney is the excretory organ, which is metanephric, urine is semi-solid
  • They have relatively large-sized eyes which powerful with a specialized structure known as pectin
  • All the birds are oviparous and exhibit sexual dimorphism
  • The matured female lay eggs with a large amount of yolk
  • Only legs are covered with scales, usually with four toes on each foot
  • Teeth are not present in the mouth. In this case, food is swallowed unmasticated
  • The skin is thin, loose, and dry with flight muscle in the thorax; the sweat gland is absent
  • The respiratory system can perform double respiration. In this case, air sacs are connected to the lungs, which ensure supplement respiration
  • Birds perform internal fertilization
• Flight Adaptations in Class Aves

  • Feather - They provide the passage for air and reduce friction to minimum. They also prevent loss of heat and help to maintain a constant temperature
  • Beak - Besides procurement of food, the beak is also used for nest-building
  • Wings - Fore-limbs are modified into wings, which help during flight
  • Body - Its spindle-shaped body is designed to offer minimum resistance to the wind
  • Hind Limbs (Legs) - They are well suited for perching
  • Endoskeleton - Most of bones are pneumatic and filled with air instead of bone marrow. It makes the body light. Most of bones are firmly fused together, which help in flight
  • Flight Muscles - The flight muscles on the breast are greatly developed which help in flight
  • Neck and Head - Mobile neck and head are very useful for feeding, nest building, offence and defense
  • Air Sacs - These are attached to lungs which serve as reservoirs of air. They may also aid as cooling devices in regulation of the temperature of the body
  • Warm-Bloodedness - Birds are warm-blooded animals which is necessary for flight
  • Circulatory System - A large oxygen supply is required for rapid metabolism and warm-bloodedness. It is done by an efficient circulatory system
  • Absence of Urinary Bladder - Except Rhea, urinary bladder is absent in birds. Excreta are passed out at once. This helps in reducing the weight of the body
  • Brain and Eyes - Brain and eyes are well developed. Equilibrium is maintained by well developed cerebellum of the brain
  • Single Ovary - Presence of a single functional ovary on the left side in the female bird also leads to reduction of weight which is so essential for flight
• Class Mammalia


  • Animals belonging to class Mammalia are referred to as mammals
  • They exhibit advanced characteristics which set them apart from all other animals
  • They are characterized by the presence of mammary glands through which they feed their younger ones
  • They are distributed worldwide and have adapted well to their surroundings – from oceans, deserts and polar regions to rainforests and rivers etc.
• Classification of Mammals


  • Eutheria - Mammals under this subclass give birth to young ones. The young ones are developed inside the mother and derive nutrition through the placenta from the mother. This subclass consists of 19 orders including Proboscidea (Elephants), Rodentia (Rats), Artiodactyla (Cows)
  • Metatheria - Mammals belonging to this sub-class give birth to immature young ones, hence they stay in their mother's pouch until they mature. This subclass consists of 7 orders including Notoryctemorphia (Marsupial modes), Diprotodontia (Kangaroo), Microbiotheria (Colocolo), Didelphimorphia (New world opossum), Dasyuromorphia (Dasyurids), Peramelemorphia (Bandicoots), Paucituberculata (South American rat opossum)
  • Prototheria - Also known as Monotremes, the sub-class Prototheria consists of egg-laying mammals. Monotremata is the only order in Prototheria, which includes the duck-billed platypus and four species of echidna (also known as spiny anteaters)
• General Classification of Mammals

  • Animals (e.g. Lion, Tiger, Dog)
  • Marsupials (e.g. Kangaroo, Koala, Womba)
  • Primates (e.g. Chimpanzee, Gorilla, Monkey)
  • Rodents (e.g. Squirrel, Mouse, Porcupine)
  • Cetaceans (e.g. Dolphins, Whales)
  • Other Mammals (e.g. Seal, Walrus, Sea-lion)
• In part because of their high metabolic rates, mammals often play an ecological role that is disproportionately large compared to their numerical abundance
• Many mammals maybe keystone predators in their communities or play important roles in seed dispersal or pollination
• Despite their low species diversity, compared to other animal groups, mammals have a substantial impact on global biodiversity
• Ecosystem Impact of Mammals

  • Seed dispersal
  • Pollination
  • Creates habitat
  • Biodegradation
  • Soil aeration
  • Keystone species