Class Mammalia

Mammals (class mammalia) are one of the most evolved species in the animal kingdom categorized under vertebrata. 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 land, oceans, deserts and polar regions to rain-forests and rivers etc.

Characteristics of Mammals (class mammalia)

Following are a list of distinct characteristics of mammals that separates them from other classes:

  1. Mammals are warm-blooded animals who give birth to their younger ones.
  2. They are the most dominant form of animals found in almost all types of habitats.
  3. They have mammary glands that help them produce milk to feed their younger ones
  4. Presence of region of the brain known as Neocortex (largest part of the cerebral cortex).
  5. Their skin possesses oil glands (sebaceous glands) and sweat glands (sudoriferous glands).
  6. The fur of hair throughout the body which helps animals adapt to their environment.
  7. They are heterodont. i.e. possess different types of teeth.
  8. Mammals also possess cervical vertebrae.
  9. The skull is having two occipital condyl in mammals.
  10. The trunk is divided into thorax and abdomen.
  11. The mammals respire through lungs.
  12. Good sense of hearing as mammals are aided with 3 middle ear bones
  13. Mammals have a four-chambered heart. The sinus venous and renal sinus portal system is absent.
  14. Presence of single-boned lower jaws.
  15. The brain is well developed divided into cerebrum, cerebellum and medulla.
  16. They possess 12 pairs of cranial nerves.
  17. Exhibit one of the most advanced forms of Diaphragms.
  18. The mammals can lay eggs also. They are known as viviparous.

Classification in Mammals

Mammals are classified into three subclass based on their reproduction method as follows:

  1. Eutheria (Monotremes)
  2. Metatheria (Marsupials)
  3. Prototheria (Placentals)

Sub-class Prototheria

Prototheria consists of egg laying animals and are also known as Monotremes.

This subclass consists of six species all in one order.

Example – Duck-Billed Platypus and Echidna or Spiny ant-eater.

Features of subclass Prototheria:

  1. External pinnae are absent.
  2. In the young stage, teeth are present, and horny plaques form in adults.
  3. Mammary glands are present and teats are absent.
  4. Body is covered by hairs.
  5. Corpus callosumis absent in brain.
  6. Cochlea is simple and is not coiled.
  7. In the males the testis is abdominal hence scrotal sacs are absent. Seminal vesicles and prostrate are absent.
  8. Ureters open into the cloaca.
  9. Females are egg laying. Hence prototheriansare called egg laying Mammals.
  10. They are called unfinished mammals as they possess several reptilian characters.
  11. They are also considered to be living fossils.

Sub-class Metatheria

Mammals that belong to this subclass also give birth to their young ones but the young ones are born immature. So they migrate into their mother pouch and stay their till they are mature. These are also known as Marsupials.

Metatheria subclass contains seven orders with 250 species.

Example – Marsupials, kangaroo, Opossum, etc.

Features of Subclass Metatheria:

  1. They first evolved in South America some 100 million years ago when Australia, South America and Antarctica were joined together. Gradually, these three continents separated and the marsupials got isolated. They freely evolved in isolation.
  2. The term marsupium means a pouch. Marsupium is present in females.
  3. Marsupial bone is present.
  4. Mammary glands are developed.
  5. Corpus callosum is poorly developed.
  6. Vagina and uterus and the penis are double.
  7. Placenta is absent. Viviparous.
  8. Marsupials give birth to a relatively undeveloped young, which often resides in the pouch with the mother for a certain time after birth. This also implies that they have a relatively short gestation.
  9. Marsupials have different ecological niches, ranging from moles to insects eaters to plant eaters.
  10. Most Marsupials are nocturnal and they have a good sense of smell and hearing.
  11. With the exception of tree kangaroos, all members of the kangaroo family rely on long, powerful hind legs and feet for hopping and leaping, their predominant forms of locomotion.
  12. Marsupials having long tails, thickened at the base, serve for balancing. This feature is most evident in large kangaroos, which use their tail as their third leg when stationary.

Sub-class Eutheria

Mammals that give birth to their young ones directly belong to the subclass Eutheria. The young ones form as an embryo in the mother uterus and grow there for a certain period of time. These are also known as Placentals.

Placentals are the most evolved mammals. With over 5000 species, placentals are far the largest of the three mammal groups.

Placental babies spend a long time developing in their mother’s womb. While in the womb they are nourished by a spongy organ called the placenta. When born, they are usually fully formed.

Placentals are divided into about 19 different group called order.

Below are the 8 major orders:

Order Artiodactyla

  • These are even toed ungulates.
  • They have ungulates walk on their toes.
  • Most are specialized for cursorial locomotion with long hoofed legs, and have diversified as the perssodactyls have declined.
  • Number of teeth is variable but they have a diastema.
  • Males often sport antlers or horns.
  • Example – Deer, Sheep, Javelina, Antelope, Cows, Hippopotamuses, Camels, Giraffes.

Order Perissodactyla

  • These are odd toed ungulates.
  • Example – Horses, Rhinoceroses, Zebras.

Order Carnivora

  • Although not all current carnivora are carnivorous, the ancestors were meat eaters.
  • Recognizable carnassial apparatus for shearing meat and tendons (between the 4th upper premolar and 1st lower molar), keen senses, and large brain.
  • Teeth is in count of 3 upper and 3 lower incisors.
  • Carnassial theeths are slide past each other in a scissor-like fashion as the mouth is closed and adapted for shearing flesh.
  • Example – Dogs, Cats, Bears, Raccoons.

Order Insectivora

  • This order is third largest order of mammals and possibly the most primitive group (mesozoic mammals are rather shrew-like).
  • Example – Moles and Shrews.

Order Lagomorpha

  • This order resemble large rodonts with short tails.
  • Flaps of skin can close behind the insisors and close the nostrils.
  • Teeths with 2 upper incisors, one behind the other.
  • They have fenestrated skull.
  • Example – Rabbits.

Order Rodentia

  • They chisel with their teeth. Rodents have sharp front teeth that keep growing throughout life. These chisel-like teeth are used both to gnaw their food and to cut through obstacles.
  • These are the largest order of mammals (40% of mammal species).
  • Individual having upper and lower incisors that are rootless and grow throughout life for a gnawing life style.
  • Example – Squirrels, Chipmunks, Rats, Mice, Beavers, and Porcupines.

Order Chiroptera

  • This order contains all the species of bats. About 1000 species are their in order chiroptera.
  • These flying mammals help control insect populations. Most bats are small, but some fruit eating ones have a wingspan of over 1.5 m (5 ft).

Order Primates

  • Primates that includes us.
  • Primates include lemurs, monkeys, apes, humans. They have a mixed diet and most species live in trees.
  • Example – Humans, Gorillas, Orangutans, Chimpanzees, Baboons, Mandrilles, Lion Tamarin.

People also ask about Mammals

1. Why bat is a Mammal?

Answer Bat is not a egg laying animal. They give birth to new young one and having mammary glands which is key character of mammals.

2. Give the examples of subclass Prototheria.

Answer Almost all the species of subclass prototheria are extinct; only Duck-Billed Platypus and Echidna or Spiny Ant-eater are alive.

3. What are key characters of class mammalia?

Answer1. Presence of Mammary Glands.
2. Presence of Sweat Glands.
3. Presence of three ear bones.
4. Presence of 3 chambered heart.

4. Enlist the examples of Mersupials?

AnswerMarsupials includes pouch animals like Kangaroo, Opossum, Koala, Quokka, Wombats, Wallabies, Bandicoots etc.

References and Sources

Further Readings

  1. Chromosome
  2. Chromosomal Aberration
  3. Class Reptilia
  4. Mendelian Inheritance
  5. Phylum Chordata
  6. Types of Chromosomes