General characters and classification up to Orders
1. These animals are warm blooded, hairy and have mammary or milk producing glands,
(mammary glands). They are the only animals which nourish their young ones with milk.
There are about 4,000 species of mammals found in the world.
2. They are homoiothermous (warm blooded).
3. Oil glands (sebaceous glands) and sweat glands (sudoriferous glands) are present in the
skin.
4. Teeth are of different types (heterodont) and are embedded in the sockets of jaws (the
codont). These are developed twice during the life-time of the animal (diphyodont), milk
and permanent teeth.
5. Except a few, mammals possess seven cervical (neck) vertebrae.
6. The skull is dicondylic i.e., with two occipital condyles.
7. Respiration is by lungs.
8. They possess a muscular diaphragm dividing trunk into thorax and abdomen.
9. The coelom is divided into four cavities; a pericardial cavity lodging the heart, two
pleural cavities each containing the lung and an adominal cavity having the rest of
viscera.
10. The heart is four chambered. Sinus venosus is absent. The red blood corpuscles are
without nucleus. Renal portal system is absent.
11. The brain has large cerebrum and cerebellum. Optic lobes are divided into four lobes
called corpora quadrigemina. Corpus callosum connects the two cerebral hemispheres
internally.
12. 12 pairs of cranial nerves are present.
13. Each ear consists of three parts: external, middle and internal. Pinna is a part of external
ear. Middle ear has 3 bony ear ossicles (malleus— hammer shaped, incus-anvil shaped
and stapes-stirrup shaped). Internal ear has organ of Corti, the actual hearing organ.
14. Except egg laying mammals they are viviparous. There are present four embryonic
membranes: chorion, amnion, allantois and yolk sac. Except egg laying mammals a well
developed placenta is present.
15. Mammals occur in all sorts of habitats. They are dominant animals and are capable to
learn because of their better developed brain.
Examples:
Oviparous – Omithorhynchus (Duck Billed Platypus), Tachyglossus = Echidna (Spiny Anteater).
Viviparous — Macropus (Kangaroo), Pteropus (Large bat), Camelus (Camel), Macaca
(Monkey), Rattus (Rat), Canis (Dog), Elephas (Elephant), Felis (Cat) Delphinus (Common
dolphin), Equus (Horse), Balaenoptera (Blue whale), Panthera tigns (Tiger), Panthera leo (Lion).
Class Mammalia divided in to two Subclasses :-
1. PROTOTHERIA
2. THERIA
1. Sub Class: Prototheria
Prototherians are considered to be the most primitive mammals which are only restricted in
Australia and its neighbouring islands (Tasmania New Guinea). Besides egg-laying habit, they
have several reptilian characters including a cloaca. They lay eggs containing ample amount of
yolk. Subclass prototheria includes one order Monotremata e.g., Omithorhynchus, Tachyglossus-
(Echidna).
Ornithorhynchus (Platypus) Tachyglossus (Echidna)
2. SUBCLASS THERIA
Viviparous mammals. They produce young ones. Subclass theria is divided into two
infraclasses; Metatheria and Eutheria.
It is further subdivided in to 2 infraclasses:-
I. METATHERIA
II. EUTHERIA
I. Infra Class: Metatheria (Pouched mammals):
ORDER MARSUPIALIA :
Born in very immature state and complete their development attached to teats in the
marsupium.
3 premolars and 4 molars in each jaw on either side.
Macropus (kangaroo) Phascolarctos (koala)
II. INFRACLASS EUTHERIA (Placental mammals)
i). ORDER INSECTIVORA
Small mammals with long pointed snout.
Feet plantigrade (walking on the sole of the feet) with claws.
Molars with pointed peg (a short pin typically tapered at one end)like cusps (pointed end
where two curves meet).
Placenta discoidal (resembling a disc).
Nocturnal and terrestrial.
ii) ORDER CHIROPTERA (Flying mammals)
Forelimbs are modified into wings called patagium(membrane or fold of skin between
fore and hind limbs of a bat or gliding mammal).
Teeth small, sharp, peg like.
Sternum provided with keel.
Eyes are small with weak vision.
Ear have large pinnae.
nocturnal
Myotis (brown bat) Pteropus (fruit bat)
iii) ORDER DERMOPTERA
Four equal sized limbs.
Tail included in a furry skin fold, the patagium (The thin membrane that extends between
the limbs and body of a bat or of gliding mammals).
Incisor teeth 2\3.
Nocturnal
Cynocephalus
iv) ORDER PHOLIDOTA
Body covered with large overlapping horny scales.
No teeth
Tongue long and protrusible.
Manis (scaly ant eater)
v) ORDER EDENTATA
Teeth absent or reduced to molars, without enamel.
Toes with large, strong, curved claws.
Some times they are armoured.
Myrmecophaga (giant anteater) Dasypus (armadillo)
vi) ORDER TUBULIDENTATA
Tongue tough, slender, protrusible.
No incisors or canines.
Each jaw with 4-5 teeth, lacking enamel and perforated by numerous fine tubules of pulp.
Skin thick covered with hairs.
Placenta zonary
Orycteropus (cape anteater)
vii) ORDER PRIMATES
Primitive mammals except for the development of brain.
Flat nails on fingers and toes.
First digit usually opposable, an adaptation for grasping.
Eyes typically large and turned forward.
Mostly arboreal
Lemur Tarsius Chimpanzee
viii) ORDER RODENTIA
Largest order including usually small gnawing (chew on, or erode with the teeth)
mammals.
Each jaw with one pair of long, rootless, chisel(long blade having sharp edge used to chip
or cut solid material) like incisors.
No canines
Digits provided with claws.
Space between molars and canine called diastema.
Rattus Cavia (guinea pig) Hystrix (porcupine)
(rat)
ix) ORDER LOGOMORPHA
With a second pair of small upper incisors behind first pair of large chisel (a tool with a
cutting edge on one end) like incisors.
No canines
Ochotona (pika) Oryctolagus (rabbit)
Lepus (hare)
x) ORDER CETACEA
Large, marine, fish like mammals, well adapted for aquatic life.
Hairs on skin are reduced to a few bristles on muzzle (forward projecting part of the head
of certain animals; includes the jaws and nose).
Pectoral limbs modified in to broad paddle like flippers.
No claws, no hind limbs, no external ears.
Skull bones are spongy and contain oil.
Balaenoptera (blue whale) Delphinus (dolphin)
xi) ORDER SIRENIA
Large, clumsy(bulky, awkward in movement), herbivorous, aquatic mammals with
paddle like fore limbs, no hind limbs.
No external ears
Muzzle(projecting part of face including nose and mouth) blunt
Stomach complex having several chambers.
Inhabit estuaries and coastal sea.
Trichechus (manatee) Dugong
xii) ORDER CARNIVORA
Small to large predatory flash eating mammals.
Claws well developed
Incisors small, canines large, fang like and molars of cutting type.
Temporal fossa (a shallow depression) are open behind.
Tympanic bulla (A vesicle, or other thin-walled cavity) are large and rounded.
Odobenus (walrus) Panthera tigris (tiger)
xiii) ORDER HYRACOIDEA
Small, guinea pig like mammals, distantly related to elephants.
Snout, ears and legs short.
4 toes on front foot, 3 on hind foot, each with a flattened hoof like nail.
Incisors 1\2, no canines.
Cheek teeth lophodont (Having molar teeth that have ridged grinding surfaces).
Hyrax (conies)
xiv) ORDER PROBOSCIDEA
Largest living land animals having large heads, massive ears, thick hairless skin, bulky
straight legs and 3-5 toes with small, nail like hoofs.
Conspicuous feature is the nose and upper lip modified as an elongated flexible
proboscis or trunk.
2 upper incisors elongated as ivory tusks.
Cheek teeth lophodont.
Elephus (elephant)
xv) ORDER PERISSODACTYLA
The odd toed hoofed mammals or ungulates have an odd number of toes (1-3).
Functional axis of foot passes through the middle or third digit.
Incisors present in both jaws.
Stomach simple
Tapirus (tapir) Equus zebra Rhinoceros
ORDER ARTIODACTYLA
The even toed hoofed mammals having an even no. of toes (2-4).
Axis of support passes between third and fourth toes.
All chew their cud (that portion of food which is brought up into the mouth by
ruminating animals from their first stomach, to be chewed a second time) except
pigs and peccaries (skunk pig).
Incisors and canines in upper jaw usually lacking.
Stomach 4 chambered.
Many with antlers and horns.
Hippopotamus Ovis (sheep)
Footnote: The study material was taken from literature is freely available on internet. The purpose of this study
material is solely for teaching.
All the copy rights are with the concerned web sites, authors, Wikipedia , Prof. Usmani and I don’t have any claim
on language or content of this article. The information provided in this article is correct to the best of my
knowledge, but I apologize for any factual mistake, if occurred and I welcome the corrections/suggestions from
everyone.
Thank- Dr. Yasir Akhtar Khan
