Class: Mammalia | Additional Study Material for NEET PDF Download

Introduction

• Animals belonging to class Mammalia are referred to as mammals. Mammals are one of the most evolved species in the animal kingdom categorized under vertebrata.Class: Mammalia
• 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.

Characteristics of Class Mammalia

– Evolved in Triassic period of Mesozoic era.

– Coenozoic era is golden era of mammals.

– Study of mammals is known as Mammology.

– The members of this class are cosmopolitan, Homeiothermal, Endothermic.

– Skin of mammals is thick, waterproof, glandular

–   Epidermal hairs are present. These act as thermo resistant layer and helps in maintaining internal body temperature. In aquatic mammals, hairs are lost and homeothermic condition is maintained by layer of sub-cantaneous fat.

–   Mainly two types of glands are found in skin - sweat and sebaceous glands.

–   Sweat glands release sweat and help in regulating body temperature. It is excretory in nature also.

–   Sebaceous glands release only secretion and keep the skin and hairs water-proof.

– Body is divided into head, neck, trunk and tail.

– A horizontal, diaphragm is present in the body cavity of all the members of this class without any exception.

This diaphragm is present in between thorax and abdomen.

Diaphragm helps in respiration, defaecation, micturition and parturition.

– So many types of glands are present in the skin as sweat glands, oil glands or sebaceous glands and mammary glands.

– Mammary glands are modified sweat glands found in females for baby feeding and on the basis of this, the class mammalia was so named.

– Other skin derivatives such as nails, claws or hoof or horns are found, which provide protection.

– Two pairs of limbs are present in trunk. Limbs are pentadactyle which help in swimming, walking running etc. Hind limbs are absent in Cetacea and Sirenia.

– Alimentary canal is complete, Anus and urinogenital apertures are separate. Cloaca is absent except in subclass - Prototheria.

– Teeth are Thecodont, Heterodont, diphyodont.

– Jaw suspension is Craniostylic type

– Lower jaw is made up of dentary bone.

– Paired pulmonary resp. by paired lungs enclosed in pleural cavity.

– Larynx or sound organ is found in the trachea for the production of sound.

– Heart four-chambered. Double circulatory system is present. No sinus venosus. Only left aortic/systemic.

– RBCs small, circular and enucleated. Family Camilidae-Lama and Camel which has nucleated RBCs.

– Endoskeleton is bony, skull is dicondylic.

– Vertebrae are acoelous or amphiplatyan type i.e. centrum is flat at both the sides. Epiphysis is present on either side of centrum & long bones.

– Neck is having 7 cervical vertebrae : (Bradypus/Sloth has 9 or 10 cervical vertebrae and Sea - cow/Mantees has 6 cervical vertebrae.)

– Ribs are bifid.

– Paired Metanephric kidneys localed in abdominal cavity.

– These animals are ureotelic.

– Brain is comparatively large and highly developed.

– Cerebrum and Cerebellum are very complex in structure and highly developed.

– Corpus - callosum. (Absent in Monotermes & Marsupial) connects both the cerebral hemispheres of brain

– 4 Solid optic lobes collectively known as corpora quadrigemina are present.  

– 12 - pairs of cranial nerves.

– External ear is present in the form of ear pinna and auditory meatus (canal)

– Malleus, Incus and stapes are the three ear ossicles in middle ear.

– Cochlea of internal ear is spirally coiled. 3 pairs of semi circular canals are present.  

– Unisexual animals. Testes of males are situated (outside the body) in the scrotal sacs. A distinct penis is present in males for copulation.

– Ovaries are found in females

– Fertilization is internal and it takes place in fallopian tubes.

– Development internal occurs in uterus. Extraembryonic membranes amnion, chorion, allantois and yolk sac are found in embryos (Amniota).

– Eggs are alecithal or microlecithal & homolecithel except eggs of prototherians megalecithal.

– Placenta is present, so these animals are also called placental animals. Placenta helps in the nutrition, respiration and excretion of embryo

– Mostly mammals are viviparous. Some mammals are oviparous [Prototherians], some mammals are ovoviviparous [Metatherians]

– Parental care is well marked in mammals.

Classification of Mammals

Living mammals are classified into three sub classes:

1. Prototheria

2. Metatheria

3. Eutheria

(a) Subclass: Prototheria

– Primitive egg-laying mammals are included.

– Eggs are large, yolky and shelled. (Megalecithal)

– Mammary glands are without nipples.

– Gynaecomastism is found in these animals i.e. male and female both feed their child. Mammary glands are functional in males and females both.

– Cloaca is present.

– Testes are abdominal

– Pinnae are absent and cochlea is less coiled.

– Corpus - callosum is absent in brain.

– A toothless horny beak is found in adult animals, but teeth are present in child hood.

– These are partially homeothermic animals.

– Members of this subclass are found in Australia, New Guinea and Tasmania.

Only one order is included in this subclass.

Order - Monotremata

Connective links between reptiles and mammals.

e.g.

–    Ornithorhynchus or Duck-billed platypus - poison glands are found in male platypus.

–    Tachyglossus or Echidna or spiny anteater.

(b) Sub-Class: Metatheria or Marsupials

–    An abdominal pouch called marsupium is found in these animals, in which immature young ones are developed till maturity.

–    Mammary glands are present and nipples are also found on these mammary glands, these are situated in marsupium.

–    Two vagina, two clitoris and two uteri are present in a female animal and bifid penis present in male.

–    Yolk sac, placenta are found.

–    Cochlea is more coiled in internal ear.

–    Teeth are present in adult animals, which are monophyodont and heterodont type.

–    Corpus callosum is also absent.

Only one order is included in this sub-class

Order - Marsupialia 

Animals are ovoviviparous

–    Macropus - Kangaroo - Found in Australia only. Saltatorial locomotion (Tail to use as body balance)

–    Didelphys - Opossum - Found in North America. Shortest gastation period (12-13 days).

–    Dasyurus - Tiger cat.

(c) Sub-Class: Eutheria

– These are true mammals that give birth to a mature child. A true placenta is found, which is Allanto-chorionic type.

– Cochlea is highly coiled.

– Nipples are well developed in mammary glands.

– Uterus and vagina are single i.e. only one uterus and only one vagina are present in a female. Penis simple.

– Corpus callosum is found in brain.

– Completely endothermic animals.

Sub-class Eutheria is divided into 16 orders :-  

1. Order : Insectivora

Erinaceous  -    Jhau - Chuha/Hedge Hog

Talpa  -     Mole

2. Order : Dermoptera

Galeopithecus - Flying lemur

3. Order : Chiroptera

True Flying mammals.

Patagium present.

Ecolocation is found.

Pteropus - Flying fox, It is a fruit eater animal.

Vespertilo - Insectivorous bat, it is also called filter mice.

Desmodus - Vampire bat, it is a sanguivorous  animal

4. Order : Rodentia

These are small, terrestrial, herbivore or omnivore animals.

• Largest order

• Diastema present.

Funambulus      -    Squirrel

Rattus rattus      -    Rat

Hystrix               -     Porcupine = Sehi = Body hair are modified into quills.

Cavia                 -     Guinea Pig

Dipodomys        -   Kangaroo rat - Desert rat (Never during water)          

Beavers             -      Aquatic Rodents

5. Order : Edentata (Ant - eaters)

Insectivorous.

Bony plates or Horny Scales present.

Myrmecophaga   -        Giant ant eater.

Dasypus or Armadillo   -   It shows polyembryony. 

Bradypus    -   Slowest animal

6. Order : Pholidota

Manis/Pangolin - Scaly ant eater

7. Order : Lagomorpha

Diastema present.

Oryctolagus   - Rabbit

Lepus  - Hare

Ochotona - Pika (Tail less)

8. Order Carnivora

Canines well developed

carnassnsials  present

digitigrade.

Canis familiaris     -      Domestic dog.

Felis domesticus   -      Domestic cat.

Panthera leo persica               -      Lion - Lions in India are found only in Gir forests of Kathiawar of Gujrat state.

Panthera pardus  -      Tendua - Panther.

Panthera tigris       -      Tiger - It is the National animal of India.

Acinonyx                -      Cheetah - It is the extinct animal of India.

Vulpes   -      Fox.

Phoca  -     Seal

Ursus   -     Bear

Canis lupus  -   Wolf

9. Order : Cetacea

– Balaenoptera musculus - Blue whale - Found in Antarctic ocean. A Horny sheet called Baleen Plate
(for filtration) is found in upper jaw instead of teeth. Milk is squirited to baby by the muscle contraction of mother. Retea mirabilis is found in thoracic region which helps in respiration in under water.

Phocaena porpoise  -   Small whale

Physeter   -  Sperm whale - From its intestine Ambergris is secreted which is used in making perfumes.

Platanista gangetica   -    Dolphin - It is found in Ganga river.

Delphinus    -    Common Dolphin

10. Order : Sirenia

– Herbivorous aquatic animals

– Hind limbs absent.

– Pinnae absent.

– A transverse fin on tail.

– Big tusk in male.

Trichechus  -        Manatee

Halicore      -        Dugong

– Tubular mouth, Tounge Slender & Protrusible.

11. Order : Tubulidentata

Orycteropus - Aardvark - It is found in Africa

12. Order : Proboscidia

Largest, heaviest

Upper incisors – Tusk

Lophodont

– Molar teeth are lophodont type.

Abdominal testes.

Elephas        -               Indian elephant    

Loxodonta   -              African elephant, it is largest living land animal.

13. Order : Artiodactyla

– Stomach is four chambered, (ruminant stomach) it helps these animals in rumination (Cud-chewing). All animals are Ruminant except pig and Hippopotamus (Nonruminant). Eventoed ungulate animals.

Bos indicus         -  Cow

Bubalus bubalus -  Buffalo

Camelus              -  Camel [RBC nucleated]

Sus               -  Pig

Capra          -  Goat

Ovis            -  Sheep

Bos mutus -  Yak

Cervus         -  Dear

Camelo paradelis             -  Giraffe

Moschus moschiferus      -  Musk dear (Smallest RBC)

14. Order : Perissodactyla

Odd.toed unguligrade

Equus caballus   -  Horse

Equus asinus      -  Donkey

Equus hemionus -  Indian Donkey

Equus zebra -  Zebra

Rhinoceros unicornis      -     Rhino - Single horn Genda. It is found in Kaziranga National Park Jorhat, Assam Rhino posses keratin hornoversnout.

15. Order : Primata

– Most developed mammals. Plantigrade, large and highly convoluted cerebral hemispheres. It includes most intelligence animals e.g. man, monkeys, lemur, apes, gibbons, gorilla chimpanzee.

(a)  Prosimians

–    Nycticebus      -    Lemur

–    Loris               -     Loris (tail less)

–    Tarsius            -     Tarsier

(b)  Simians

–    Hylobates  -   Gibbon - smallest ape. (found in India)

Only ape found in India-Hoolock gibber

16. Order: Hyracoidea

Hyraxes, also known as dassies or conies, are jack-rabbit sized animals with short tails and peculiar, 3-toed hind feet with almost hoof-like nails on two of the toes (the inner toe has a claw). They have specialized muscles in the soles of the feet that help them to work almost like a suction cup.