Mammals Class mammalia divided into two subclasses 1

Mammals Class mammalia divided into two subclasses… 1. Prototheria: Primitive, reptile like, oviparous mammals. 2. Theria: modern typical viviparous mammals. A. Infraclass: Metatheria: (Marsupial Mammals) Pouched & Viviparous mammals, confined mostly Australian region. B. Infraclass: Eutheria: (Placental mammals) Higher Viviparous, without marsupium. These constitute the vast majority of living mammals.

• Important features of Protothria: • Most primitive egg-laying mammals. • Aquatic or terrestrial, burrowing, nocturnal & insectivorous. • Body texture is small & covered by hairs & spines. • The external ear or pinnae are absent. • Snout is produced into beak or rostrum. • Tail may or may not be present. • The mammary glands are not specialized without teats & are the modified sweat glands. • Skull is dicondylic. • Seven cervical vertebrae without zygapophyses.

• Teeth are absent in adult, they are present in embryonic stages & are replaced by horny plates. • Rostrum opens in to cloaca. • Heart is 4 chambered. • Partly homothermous, temp ranges between 25 to 28 o C. • Brain is simple. • Kidneys are metanephric, ureters opens into a urinogenital sinus which terminates into cloaca. • Testes are abdominal in position. • Penis is retractile , only sperms passed out but not urine.

• The ovaries are of unequal size, the oviducts open separately in cloaca. • The Uterus is absent, a temporary breeding pouch is formed during breeding season. • Fertilization is internal. • Egg laying mammals, newly hatched young ones are immature & fed on the secretion of glands on ventral abdominal wall.

• Similarities of Prototheria with Reptiles & Mammals): • Similarities with REPTILES: 1. 2. 3. 4. 5. 6. 7. External ear is absent. Cloaca is presnt. Oviparous condition. Large eggs, megalecithal with leathery shell. Vertebrae without epiphysis. Ureter & urinary bladder opens separately. Body temperature is not constant.

• Similarities with MAMMALS: • Skin is covered with hair & with sweat & sebaceous glands. • Skull is dicondylic. • Body is well divided into thoracic & abdominal cavities. • Three ear ossicles are present in middle ear. • Seven cervical vertebrae are present. • Liver is a lobed structure. • Heart is with 4 chambers. • RBC’s are non nucliated & a single aortic arch is present. • Four optic lobes are present in the brain.

Duck-billed Platypus Echidna

Metatheria • Metatherians are primitive types of mammals. • Metatherians or marsupial mammals are confined to Australia, South America but majority of them are found in Australian region. • The giant Kangaroo (Macropus) & Opossum (Didelphis) are the commonest examples. • In America only American Opposum is found.

• Important features of Metatheria: • Body is covered with soft hairs. • External ears or pinnae are present. • Mammary glands with teas & present in the abdominal pouch or marsupium of female. • Tail is long & prehensile. • Hind limbs are comparatively longer than fore limbs. • Skull is dicondylic with small cranium. • Tympanic bulla is absent. • Mandible is made up of dentary, a single bone. • Middle ear with 3 ear ossicles.

• Seven cervical vertebrae are present in neck region. • A long marsupial bone is present infront of symphysis of pelvic girdle. • Ribs are bicephalous. • Teeths are monophyodont, heterodont or homodont. • Anus & Urinogenital aperture open into a shallow cloaca. • Heart is 4 chambered. • Brain is small & poorly developed. • Kidneys are metanephric. • Male genital organ well developed & bifurcated at tip. • Testes are extra-abdominal in scrotal sacs.

• Two oviducts open into urinogenital sinus & hence two uteri & two vaginae. • Viviparous animals. • The young ones are born in immature condition. • Development takes place in uterus but true allantoic placenta is absent. • Gestation period is small, about 2 -5 weeks. • Young ones born are blind and kept in the marsupial pouch of the female & nourished until fully developed.

Kangaroo Opossum

Eutheria (Placental Mammals) • Hair-clad, mostly terrestrial, air breathing, warm blooded, viviparous, tetrapod vertebrates. • Body divisions are head, neck, trunk & tail. • Limbs 2 pairs, pentadactyle, each with 5 or fever digits. • Variously adapted for walking , running, climbing, burrowing, swimming or flying. • Hind limbs absent in Cetaceans & Sirenians. • Exoskeleton includes horny epidermal hairs, spines, scales, claws, nails, hoofs, horns, bony dermal plates. • Skin richly glandular containing sweat, sebaceous & sometimes scent glands.

• Mammary glands well developed with teas, producing milk for nourishing young ones. • A muscular diaphragm, separates the anterior thoracic from posterior abdominal cavity. • Endoskeleton is ossified. Skull dicondylic. Cranium large. • Dentary articulating with squamosal of skull. • Cervical vertebrae usually 7. • Ribs bicephalous. • Cloaca absent. • Teeths are of several types. • Respiration always pulmonary.

• Glottis protected by a fleshy and cartilaginous epiglottis. • Larynx contains vocal cords. • Heart 4 chambered with double circulation, R. B. C. small, circular & non nucleated. • Kidneys metanephric. Ureters open into a muscular urinary bladder. • Excretion is urecotelic. • Brain highly developed. Cranial nerves 12 pairs. • Senses well developed. Eyes protected by lids. • External ear opening well protected by fleshy pinna. • Sexes separated. Sexual dimorphism usually well marked.

• Testes are extra abdominal, placed in a bag (Scrotum), • Eggs are small, micro or alecithal and devoid of shells. • Fertilization is internal, preceded by copulation. • Except egg laying monotremes mammals are viviparous. • Development is uterine. Placenta provided nutrition to foetus. • Embryonic membranes i. e. amnion, chorion & allantois are present. • Parental care well developed.