Class Mammalia

Mammalia is a class of the Kingdom Animalia. The organisms belonging to the class Mammalia are called mammals. The mammals have unique characteristics, such as mammary glands for milk, warm-blooded, and different types of teeth. The body parts of all mammals are similar, including the limbs, digestive systems, lungs for breathing, circulatory systems with a heart, kidney excretions, and taste organs. About 6000 different species of mammals can be found in deserts, seas, polar regions, rivers, and rainforests.

Types of Class Mammals

Class Mammalia represents the most evolved group of vertebrates, exhibiting high intelligence, complex behaviour, and advanced physiological systems. Their adaptability and diversity make them an essential part of the natural ecosystem.

Mammals are broadly classified into three categories:

• Marsupials: Most of the marsupials have pouches, and they give birth to poorly developed young ones. Kangaroo is an example.
• Egg-laying Monotremes: They lay eggs with soft shells. Platypus is an egg-laying monotreme.
• Placentals: Humans and whales are examples of Placental Mammals. They give birth to well-developed young ones.

Characteristics of Class Mammals

The distinguishable characteristics make mammals different from other animals. The characteristics of mammals are as follows:

• Presence of mammary glands that produce milk for the offspring.
• Warm-blooded.
• Most mammals have red blood cells without a nucleus (except for camels and llamas).
• Breathe through lungs.
• Muscular diaphragms.
• It has a circulatory system with a four-chambered heart.
• The renal portal and sinus venous systems are absent.
• Diphyodont (two sets of teeth).
• Different types of teeth: heterodont and thecodont.
• Skin is covered in hair.
• Presence of sweat and oil glands on the skin.
• Presence of external ears (pinna).
• Dicondylic Skull.

Subclasses of Mammals

The Mammalia is the largest class in the Animalia Kingdom. There are several types of mammals, such as small, large, and marine mammals etc.

Based on reproduction, mammals are grouped into two subclasses:

1. Prototheria

The most primitive type of mammal is Prototheria, also known as Monotremata. These are restricted to Australia and nearby places such as Tasmania and New Guinea. Prototheria are unique due to their egg-laying nature. Monotremata is an order under subclass Protheria that consists of six species.

Example: Ornithorhynchus (Duck-Billed Platypus) and Tachyglossus (Echidna)

2. Theria

It includes animals that give birth to their children. Two infraclasses of this subclass are Metatheria and Eutheria:

Metatheria

Animals belonging to Metatheria are called marsupium marsupials or pouched mammals. The female animals belonging to this infraclass have pouches. The offspring of these mammals are immature and live in their mother's pouch until adulthood. The infraclass Metathesis is divided into 7 orders as follows:

• Notoryctemorphia
• Diprotodontia
• Microbiotheria
• Dasyuromorphia
• Paucituberculata
• Peramelemorphia
• Didelphimorphia

Metatheria has more than 250 species found in Australia, Papua New Guinea, and some parts of the United States. E.g.: Kangaroos, koalas, etc

Eutheria

Mammals that give birth to the child directly belong to the infraclass Eutheria. An embryo formed inside the mother's stomach develops into an offspring. These offspring get their nutrition inside the mother's womb through the placenta. This infraclass is divided into 19 orders.

The following table lists the orders of Eutheria:

Features of Class Mammalia

1. Limbs

• Two pairs of legs with as few as five toes.
• Have nails, claws, or hooves.
• These limbs are used for different types of activities such as running, swimming, jumping, climbing, etc.

2. Digestive System

• Slightly smaller mouths.
• Have lips with little movement.
• Presence of heterodont teeth.
• Presence of a true salivary gland in the mouth.

3. Respiratory System

• Elastic and spongy lungs.
• The respiratory system is made up of rib muscles and the diaphragm.

4. Circulatory System

• Closed circulatory system.
• Oxygenated blood is sent from the heart to different parts of the body.
• Presence of hepatic portal.
• Absence of renal portal.
• Red blood cells are concave, circular, and non-nucleated in most mammalian species.

5. Excretory System

• Presence of a pair of bean-shaped, metanephric kidneys.
• Ureotelic animals (excrete urea).

6. Sense Organs

• The olfactory sacs open into the pharynx through the internal nasal passages.
• Presence of movable lids in the eyes.
• Presence of three bony ear ossicles (malleus, incus, and stapes) in the middle ear.
• Presence of an organ of Corti in the internal ear.

Examples of Class Mammalia

A group of vertebrate animals are known as mammals. A few examples are:

• Cats
• Dogs
• Apes
• Whales
• Dolphins
• Monkeys

Some Interesting Facts About Class Mammals

• The goat has the highest body temperature having mammals.
• Embryos of mammals have the "Atlantis" that helps in respiration.
• Echidnas and Duckbilled Platypus are egg-laying mammals.
• Hemichordates excrete through the glomerulus.
• The Orangutans are the smallest apes that look like humans.
• A bat is a flying mammal.

Related Articles:

• Kingdom Protista
• Kingdom Fungi
• Kingdom Plantae
• The Living World – Introduction, Classification, Characteristics, FAQs
• Difference Between Phylum and Class