Mammalia: General Characters and Classification
GENERAL CHARACTERS:
1. Mammals are warm blooded animals.
2. The skin is more or less covered with hairs (except Cetacea).
3. Sudoriporous (sweat) glands and sebaceous (oil) glands are present in the skin.
4. Mammary glands in females, whose function is that of nourishing the young, are also present.
5. External ears (pinnae) are present.
6. Teeth are heterodont (differentiation into incisors, canines and molars), thecodont (embedded in the alveolar pockets of jaw) and (only two sets of teeth, a milk set replaced by permanent set).
7. Skull with two occipital condyles which are formed entirely by the exoccipitals.
8. Skull is without prefrontals, postfrontals, quadrato-jugal, supraorbitals and basipterygoids.
9. The lower jaw is composed of a single bone, on each side, the dentary which articulates with squamosal of its side. pieces,
10. Vertebrae are gastrocentrous composed of three the centrum, and two epiphyses.
11. With few exceptions mammals possess seven cervical vertebrae.
12. The ribs articulate with the vertebrae by two heads, capitulum and tuberculum. 13. The digits in the fore and hind limbs are never more than five, but often reduced.
14. Limbs are either plantigrade or digitigrade or unguligrade.
15. Presence of a muscular diaphragm between thoracic and abdominal cavities.
16. Heart is four chambered with only a left aortic arch.
17. R. B. C. are non-nucleated.
18. Brain with four optic lobes.
19. The kidney is metanephros.
20. Penis is always present.
21. Viviporous. The young, except in monotremes, in the uterus for some time and born alive.
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CLASSIFICATION:
The classification of Mammalia has been adopted from Storer and Usinger (1957).
Subclass I-PROTOTHERIA
1. No external pinna on the ear.
2. Teeth are present only in young adults with horny beak.
3. A cloaca is present into which ureters and urinogenital sinus open.
4. Mammary glands without nipples.
5. The pectoral girdle possesses large coracoid bones and interclavicle.
6. The pelvic girdle possesses epipubic bones extending from the pelvis.
7. Vertebrae without epiphyses.
8. The ribs have only a single head, the tuberculum being absent.
9. The cervical ribs are present.
10. In the skull, tympanic bulla and lacrimals are absent; "jugal is reduced or absent.
11. There is no corpus callosum in the brain. 12. The cochlea is a simple process of the sacculus and coiled.
13. Testes are abdominal.
14. Females are oviparous.
15. Found in Australia, Tasmania and New Guinea.
Order 1. Monotremata
The general characters are same as that of prototheria.
Examples: Echidna, Ornithorhynchus.
Subclass II-THERIA
1. Includes marsupial and placental mammals.
2. Ear usually with external pinna.
3. Teeth are usually present both in young and adults.
5. Mammary glands with nipples.
6. Testes usually in the scrotal sac.
7. Vasa deferentia and bladder opening through a common urethra in penis,
8. Ureters open into the base of bladder.
9. Oviducts open into a vagina.
10. Females are viviparous.
Infraclass I-METATHERIA
1. Marsupium or brood pouch is present in the females.
2. Mammary glands are sebaceous and bearing nipples.
3. Epipubic (marsupial) bones are usually present and attached with the pubis.
4. Separate coracoid and interclavicle are absent.
5. Ribs bear two heads, tuberculum and capitulum.
6. Vertebrae with epiphyses.
7. Corpus callosum is feebly developed or absent.
8. Vagina and uterus are double (didelphic condition).
9. Viviparous.
10. Placenta is usually absent.
Order 1. Marsupialia
The general characters are same as that of Metatheria. Examples: Didelphis (Opossum), Dasyurus (Tiger cat), Caenolestes, Notoryctes (Marsupial mole), Parameles (Bandicoot), Macropus (Kangaroo).
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Infraclass II - EUTHERIA
1. Marsupium (marsupial pouch) is entirely absent.
2. Mammary glands are well developed with nipples.
3. Epipubic bones are absent.
4. Ribs bear two heads, tuberculum and capitulum.
5. Cloaca is absent.
6. Corpus callosum is absent.
7. Urinogenital organs open independently of the rectum.
8. Testes are usually contained in scrotal sacs.
9. Vagina is single.
10. Viviparous.
11. The young always nourished for a considerable time in the uterus by means of allantoic placenta and born in a relatively advanced state.
Order 1. Insectivora
1. Small and furry animals.
2. Snout usually long tapering.
3. Feet usually five toed with claws, inner toe not opposable.
4. Teeth sharp and pointed. Dental formula: i3/3, c 1/1, p 4/4, m 3/3.
5. Placenta discoidal,
6. Nocturnal and terrestrial.
Examples: Erinaceus, Paraechinus (Hedgehog), Scopanne, Talpa (Mole), Sorez, Echinosorez (Shrews).
Order 2. Department
1. Commonly known as "flying lemurs".
2. Membranes stretched between fore- and hind limbs and also between the head and the fore limb and between the tail and hind limbs.
3. Incisor teeth 2/3. 4. Nocturnal in habit.
Example: Galeopithecus.
Order 3. Chiroptera
1. Commonly known as "true flying lemurs".
2. Fore limbs are modified for flight.
3. Second and fifth digits greatly elongated, supporting the wing or flight membrane.
4. Hind limbs are weak and have clawed digits. Claws sharp and curved.
5. Eyes are small and vision weak.
6. Ears have large pinnae.
7. Teeth are sharp. Dental formula: 2/3, e 1/1, p 3/3, 3/3.
8. Sternum has a keel.
9. Mostly nocturnal in habit.
Suborder I-Megachiroptera
1. Large fruit eating bats and also known as flying foxes.
2. Snout is elongated and without nose leaf. 3. The thumb and second digits are clawed.
4. Tail is absent.
5. Dental formula: 2/2, c 1/1, p 3/3, m 2/3.
6. They live in flocks and sleep during the day on the branches of the tree, hanging head downward with wings folded.
7. Food mainly comprises fruits, eg., figs and guava.
Examples: Pteropus, Xanthorpyia, Cynopterus.
Suborder II-Microchiroptera
1. Small insectivorous bats.
2. Snout short usually with nose leaf.
3. Only thumb is clawed.
4. Tail, if present, is attached with the wing.
5. Molars with cusped crowns with transverse grooves.
6. Nocturnal and usually gregarious in habit.
7. During the day, they hang by hind claws on the branches of trees or crevices of rocks, in caves or buildings keeping the head downwards.
Examples: Magaderma, Rhinolophus, Desmodus, Eptesicus (Brown bat).
Order 4. Primates
1. Completely hairy and generally arboreal mammals.
2. Hands and feet are more or less prehensile.
3. Five digits on each hand and foot provided with flat nails instead of claw.
4. Thumb and great toe are shorter and opposable to the other digits.
5. Mode of walking is plantigrade.
6. Orbits are directed forwards and surrounded by bony ring.
7. Clavicles are always present.
8. The femur has no third trochanter.
9. Testes are enclosed in the scrotum and the penis is pendent.
10. Two pectoral mammae with teats are usually present.
11. Cerebrum is usually large and well convoluted.
12. Placenta discoidal or metadiscoidal and haemochorial.
Suborder I-Lemuroidea
1. Exclusively arboreal and nocturnal,
2. Head with a sharp muzzle.
3. The long tail is never prehensile.
4. Fore limbs are shorter than hind limbs.
5. The second toe or finger with claw but the rest of the fingers have flat nails.
6. Orbit is net surrounded by bone behind but opens into the temporal fossa.
7. Pectoral mammae are present.
Examples: Lemur, Indris, Chirogale, Chiromys (Aye aye), Loris
Suborder II Tarsioidea
1. Eyes extraordinarily developed.
2. Ears are large.
3. The limbs are extremely long, the hind limbs longer than the fore limbs.
4. The digits have adhesive pads and flat nails except the second and third toes which have claws.
5. The tail is longer than the body with a tuft at the tip.
6. Nocturnal, arboreal and insectivorous.
Example: Torsius spectrum.
Suborder III-Anthropoidea
1. Teats are always restricted to the thoracic region.
2. The orbit is completely closed behind from the lateral fossa.
3. Teeth are 32 to 36.
4. Hands and feet are prehensile except in man.
5. Fingers and toes have flat nails except in few forms.
6. The cerebral hemispheres are more highly developed and covering the cerebellum.
7. Terrestrial or arboreal and diurnal.
Examples: Monkeys, Apes, Man.
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Order 5. Edentata
1. Teeth present or absent, if present, incisors and canines are always absent.
2. Feet have well developed claws.
3. The testes are abdominal.
4. The clavicle is always present.
5. Coracoid fused with acromian.
6. Ischium unites with sacrum.
7. Lumbar vertebrae have extra articulating surfaces.
Examples: Sloth, Armadillos, American ant eaters,
Order 6. Pholidota
1. Body covered by large over-lapping horny scales.
2. Hairs are found between the scales.
3. The snout is elongated.
4. Teeth are entirely absent.
5. Tongue is long, sticky and protrusible.
6. Ears are reduced.
7. The limbs are short each bears five digits. Fore limbs have well developed claws.
8. Nocturnal and burrowing in habits.
Example: Manis (Pangolin or scaly ant-eater).
Order 7. Lagomorpha
1. Small to moderate sized mammals.
2. Two pairs of incisors are present in the upper jaw. Canines are absent.
3. Tibia is fused with the fibula.
4. Testes are always external in the scrotum.
5. Tail is short.
6. Soles of feet are hairy.
7. Toes bear claws.
Examples: Rabbits and Hares.
Order 8. Rodentia
1. Usually small mammals.
2. Limbs usually with five toes and claws.
3. The incisors, single pair, are long chisel-like and rootless and persistently growing with enamel confined chiefly to the anterior end.
4. Canines are entirely absent.
5. Space known as diastemma present between the incisors and molars.
6. Testes are usually abdominal.
7. Placenta is discoidal and haemochorial.
Examples: Funambulus (Squirrel), Rattus rattus (House Rat), Hystrix (Porcupine), Guinea pig, etc.
Order 9. Cetacea
1. Medium sized to very large aquatic mammals.
2. Body is usually spindle-shaped and fish-like.
3. The hairy covering of skin is reduced to few bristles on the muzzle.
4. Head long often pointed without neck.
5. Eyes are minute.
6. Nostrils on the top of the head and ear openings are minute.
7. Fore limbs are modified as paddles, digits are enclosed in a common integument devoid of claws.
8. Hind limbs are entirely absent.
9. Tail is long ending in two broad transverse fleshy flukes notched in the mid-line.
10. Fleshy dorsal fin is present in some forms.
11. Dorsal and tail fins have no skeletal elements.
12. A thick layer of fat (blubber) is present beneath the skin.
13. Bones of skull are spongy and contain fat.
14. Stomach is complex and consists of three or four chambers.
15. Testes are abdominal.
16. Placenta is non-deciduate and diffuse.
Examples Whales, Dolphins.
Order 10. Carnivora
1. Small to large quadrepels, terrestrial, arboreal or aquatic.
2. Teeth generally have sharp and cutting edges and the canines are well-developed.
3. The incisors are small and always on each side in each jaw. The toes or digits never less than four and they all have strong and sharp claws.
4. The temporal fossa is open behind.
5. Tympanic bulla are large and rounded.
6. The clavicles are incomplete or absent.
7. In the hand scaphoid and lunar bones are always fused.
8. The stomach is always simple, caecum, if present is always small.
9. The brain is well developed and the hemispheres are well convoluted.
10. Mammae are abdominal.
11. Placenta deciduate and zonary.
Suborder I-Fissipedia
1. The incisors are always six in each jaw and developed in many cases.
2. The canines are always very large and strong are feebly
3. The last premolar in the lower jaw known as carnassial teeth. or sctorial teeth and the last two molars are crushing.
4. Tympanic bulla is often very inflated.
5. The lower jaw has a high coronoid process and condyle is transversely elongated.
6. The clavicle is always small and some times quite rudi- mentary or even absent.
7. The digits are mostly five and never less than four. All the digits are separate and have claws.
Examples: Panthera leo (Lion), Panthera tigris (Tiger), Prionalurus bengalensis (Leopard cat), Acinonyx (Hunting leopard), Civet cat, Herpestes (Mangoose), Hyaena, Canis (Wolf), Vulpes (Fox), etc.
Suborder II-Pinnipedia
1. Marine carnivores.
2. The greater part of the limbs are enclosed within the body skin and hands and feet are fully webbed.
3. The claws are reduced and the digits are increased in number.
4. Tail is very short and useful in swimming. 5. External ear small or degenerated. Examples: Otario jubata (Sea-lion), Trichecus (Walrus), phoca (Seal).
Order 11. Tubulidentata
1. Body stout, somewhat pig-like.
2. Skin is thick and covered with sparse hairs very.
3. Snout is long and tubular with round nostrils at the tip.
4. Ears are long, erect and pointed.
5. Tongue slender and protrusible.
6. Milk teeth numerous and permanent teeth fewer.
7. Digits 4 or 5 with heavy claws.
8. Placenta is zonary.
Example: Orycteropus (Aard-vark).
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Order 12. Proboscidea
1. Largest and highly specialized terrestrial mammals.
2. The skin is thick and sparsely covered with hairs.
3. Long proboscis or trunk which is an elongation of the nose and upper lip, bearing the nostrils at the tip.
4. Eyes are small and ears are large.
5. The legs are large and pillar-like and bear five functional digits on both fore and hind limbs.
6. The incisor teeth of the upper jaw developed into great tusks.
7. Canines are altogether absent. Molars are lophodont Dental formula: i 1/0, c %. p 3/3 m 3/3.
8. Clavicle is absent.
9. The stomach is simple and the intestine is provided with caecum.
10. The cerebral hemispheres are much convoluted but they do not cover the cerebrum.
11. Testes are abdominal in position.
12. Two pectoral mammae.
13. Placenta non-deciduate and zonary.
Example: Elephas (Elephant).
Order 13. Hyracoidea
1. Small rabbit-like animals with a split snout.
2. Ears are short and the tail is much reduced.
3. Dental formula: i 1/2, e 1/0, pm 4/4, m 3/3. 4. Four digits in the fore limbs and three in hind limbs.
5. Clavicles are absent.
6. Dorsal gland is present.
7. Testes are abdominal.
8. Mammae are six pairs, four pairs inguinal and two pairs axillary.
9. Placenta is zonary.
Example: Procavia or Hyrax
Order 14. Sirenia
1. Aquatic mammals commonly known as sea cows.
2. Body streamlined or spindle-shaped.
3. Hind limbs are absent.
4. Fore limbs modified as paddles.
5. Tail flattened with lateral flukes.
6. Nostrils are on the upper surface of the snout.
7. Clavicles are absent.
8. Stomach complex, consisting of several chambers.
9. Testes are abdominal.age line
10. Two pectoral mammae are present.
11. Placenta non-deciduate and zonary.
Examples: Halicore dugong (Dugong), Trichechus (Manatees),
Order 15. Perissodactyla
1. Large-sized hoofed mammals.
2. The middle digit of fore-and hind limbs is pre-eminent carrier most of the weight. and
3. Teeth are lophodont.
4. Dorso-lumbar vertebrae are 23.
5. Stomach is simple, caecum is large and sacculated.
6. Mammae are inguinal.
7. The brain is well convoluted.
8. Placenta is diffuse and epitheliochorial.
Examples: Equas (Horse), Zebra, Tapirus (Tapir), Rhinoceros.
Order 16. Artiodactyla
1. Terrestrial and semi-aquatic mammals.
2. Fore- and hind limbs bear two rarely four digits.
3. Teeth are selenodont or bunodont.
4. Dorso-lumbar vertebrae are 19.
5. Stomach is complicated and the caecum is small.
6. Mammal are few and inguinal or many and abdominal.
7. Placenta is diffuse or cotyledonary."
Examples: Hippopotamus (Horse of river), Sua (Pig), Dicotyles (Peccaries), Camelus (Camel), Deer, Giraffe, Antelope, Cow, Buffallo, Sheep, Goat, etc.
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