Mammalia Diversity in Living Organisms
All the animals relating to class Mammalia are termed as mammals. In the animal kingdom, one of the most developed species are mammals that are categorized under Vertebrata. Around 6,000 species of living mammals are present on the planet. They are well adapted to their surroundings such as from deserts, oceans, and polar regions to rivers and rainforests, etc because of their distribution all over the world They are depicted by the presence of mammary glands which helps them to feed their offsprings.
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Main Characteristics of Mammals
Below is the list of characteristics of class Mammalia:
Sweat glands and oil glands are found on the skin.
Presence of mammary glands, which aid in the production of milk to feed their young.
All these animals are warm-blooded.
Their hearts are divided into four chambers.
The tooth comes twice in these animals (Diphyodont).
No nucleus is found in its red blood cells (except in camels and llama).
The skin of mammals has hair.
External ear (pinna) is present in mammals.
They are of different types - heterodont and thecodont.
The skull's form is dicondylic.
A four-chambered heart is found in mammals. Both the renal portal and sinus venous systems are absent.
They possess muscular diaphragms.
They respire through lungs.
Classification of Mammals
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The largest class in the animal kingdom is Mammalia. Several types of mammals are there which can be differentiated up into smaller mammals, larger mammals, and marine mammals, etc. On the basis of their reproduction, they are classified into 2 subclasses.
Prototheria
Theria
Subclass Prototheria
Prototherians are considered as the most primitive mammals and they are only restricted to Australia and its adjacent islands such as Tasmania and New Guinea. Prototheria is also named as Monotremes. This subclass includes egg-laying mammals. Prototheria includes one order that comprises 6 species.
Order: Monotremata
Example: Duck Billed platypus (Ornithorhyncus), Echidna (Tachyglossus).
Subclass Theria
The members of this subclass give birth to young ones. It is divided into 2 infraclasses -
Metatheria
Eutheria
1. Infraclass Metatheria
The females of this infraclass possess a marsupium or brood pouch and are thus known as marsupials or pouched mammals. Immature young are born to the mammals in this infraclass and remain in their mother's pouch until they reach adulthood. There are approximately more than 250 species in this infraclass and they are inhabited throughout Australia, Papua New Guinea and some parts of America.
For example, kangaroos, koalas and possums.
Metatheria Sub-class is Divided into 7 Orders Including 250 Species.
2. Infraclass Eutheria
Mammals that give birth to well developed young ones or the child directly belong to this infraclass. An embryo is formed by the young ones in their mother's stomach where they grow for a particular period of time. They derive nutrition for their growth and development from the placenta of the mother. This infraclass comprises 19 orders.
The orders of this infraclass are listed below-
Characteristics of Mammals
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Appendages:
2 pairs of pentadactyl limbs are present. In this, each foot has either 5 or fewer toes given with horny nails, claws or hooves.
They are adapted variously for running, jumping, swimming, climbing, etc.
Digestive System:
Relatively smallmouth with movable lips.
True salivary glands present in the buccal cavity.
Different types of teeth are attained by them (Heterodont).
Respiratory System:
They breathe only through the lungs which are elastic and spongy.
In breathing, both the rib muscles and diaphragm play a vital role for the purpose of respiration.
Circulatory System
The circulatory system of mammals is closed.
The heart pumps oxygenated blood which is transported to the several parts of the body.
The hepatic portal system is present while the renal portal system is not.
In most mammalian species, RBCs are concave, circular, and non-nucleated.
Excretory System:
A pair of bean-shaped kidneys are found which are metanephric.
They are ureotelic animals (excrete urea).
Sense Organ:
With the help of internal nasal passages, the olfactory sacs open far back into the pharynx.
Movable lids are present in their eyes.
An organ of Corti is present in the internal ear and 3 bony ear ossicles (malleus, incus, and stapes) are present in the middle ear.
Fun Facts of Mammalia
In a mammal, the highest body temperature is of a goat (Average 39°Celsius).
Echidna and Duck-billed Platypus are the egg-laying mammals.
Atlantis of mammalian embryos help in the purpose of respiration.
Excretion in hemichordates takes place by the glomerulus.
The smallest man like Ape is an Orangutan.
FAQs on Mammalia
1. What are the defining characteristics of the Class Mammalia?
The Class Mammalia is defined by several key characteristics that distinguish its members from other animals. The most notable features include:
- The presence of mammary glands in females, which produce milk to nourish their young.
- A body covering of hair or fur at some stage of their life.
- Being warm-blooded (endothermic), meaning they can regulate their own body temperature.
- A four-chambered heart that ensures the complete separation of oxygenated and deoxygenated blood.
- A muscular diaphragm that aids in efficient respiration.
- The presence of three middle ear bones: the malleus, incus, and stapes.
2. How is the Class Mammalia broadly classified based on reproductive methods?
The Class Mammalia is primarily divided into two main subclasses based on their method of reproduction:
- Subclass Prototheria (Monotremes): These are primitive, egg-laying mammals. The young hatch from eggs and are then nourished by their mother's milk. Examples include the Duck-billed Platypus and Echidna.
- Subclass Theria: These are viviparous mammals that give birth to live young. This subclass is further divided into two infraclasses:
- Metatheria (Marsupials): They give birth to underdeveloped young that complete their development in a maternal pouch called the marsupium. Examples include kangaroos, koalas, and opossums.
- Eutheria (Placentals): They give birth to well-developed young. The embryo develops inside the mother's uterus, receiving nourishment through a complex organ called the placenta. This is the largest group, including humans, dogs, whales, and bats.
3. What are some major orders of placental mammals (Eutheria) with examples?
Eutheria, or placental mammals, is an incredibly diverse group with many orders. Some of the most well-known orders include:
- Primates: Characterised by a large, well-developed brain and grasping hands. Examples include monkeys, apes, and humans.
- Carnivora: Predators that typically have sharp teeth and claws. Examples include lions, tigers, dogs, and bears.
- Cetacea: Marine mammals adapted for aquatic life. Examples include whales, dolphins, and porpoises.
- Rodentia: The largest order, characterised by continuously growing incisor teeth for gnawing. Examples include rats, squirrels, and beavers.
- Artiodactyla: Hoofed mammals with an even number of toes. Examples include deer, giraffes, sheep, and cattle.
4. Why are egg-laying animals like the Platypus classified as mammals?
This is a common point of confusion. Although the Duck-billed Platypus and Echidna lay eggs, which is a characteristic often associated with reptiles and birds, they are classified as mammals because they possess the two most fundamental mammalian traits. Firstly, they have hair covering their bodies. Secondly, and most importantly, the females have mammary glands that secrete milk to feed their young after they hatch. These defining features place them firmly within the Class Mammalia, despite their unique reproductive strategy.
5. What is the evolutionary significance of having a four-chambered heart and being warm-blooded?
The development of a four-chambered heart was a major evolutionary advantage for mammals. It allows for the complete separation of oxygen-rich and oxygen-poor blood. This creates a highly efficient double-circulation system that delivers more oxygen to the tissues. This high efficiency is crucial for supporting a high metabolic rate, which is required to be warm-blooded (endothermic). Being warm-blooded allows mammals to maintain a constant internal body temperature, enabling them to remain active in a wide range of climates and at different times of day or night, unlike cold-blooded animals whose activity is often dependent on external temperatures.
6. How have mammals adapted to live in such diverse habitats as oceans and deserts?
Mammals have successfully colonised nearly every habitat on Earth through remarkable adaptations. For example:
- Aquatic Mammals (e.g., Whales): They have developed streamlined bodies to reduce drag, flippers for propulsion, and a thick layer of fat called blubber for insulation in cold water.
- Desert Mammals (e.g., Camels): They are adapted to conserve water with features like the ability to tolerate large fluctuations in body temperature and produce concentrated urine.
- Polar Mammals (e.g., Polar Bears): They survive extreme cold with thick fur, a layer of insulating fat, and large paws to walk on snow.
- Flying Mammals (e.g., Bats): They are the only mammals capable of true flight, with forelimbs modified into wings.
7. Is Mammalia a Class or a Family in the taxonomic hierarchy?
In biological classification, Mammalia is a Class. The taxonomic hierarchy follows a specific order of ranks to classify organisms, from broad to specific. For example, the classification for humans is:
- Kingdom: Animalia
- Phylum: Chordata
- Class: Mammalia
- Order: Primates
- Family: Hominidae
- Genus: Homo
- Species: sapiens
A family, like Hominidae, is a much more specific grouping within an order. Therefore, Mammalia is a major class that contains many different orders and families.
