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A Mammal is a Class of Animals which have hair, are warm-blooded and nourish their young with milk. They comprise the biggest Species on Earth, including Humans. There are approximately 5,400 Species of Mammals, distributed in about 1,200 Genera, 153 Families and 29 Orders (though this varies by classification scheme).
Approximately 86 Species and 24 Subspecies, a total of 110 distinct Taxa of Mammals have already become Extinct since mankind started keeping records. Apart from these, 241 Taxa of Mammal are currently on the IUCN critically Endangered List. Another 436 Taxa are listed as Endangered and a further 776 are classed as Vulnerable. In total this means 1453 Taxa or over 25% of all Living Mammals are listed in the IUCN Red Data book. Mammals are divided into Three main Infraclass Taxa depending how they are born.
Kingdom - Animalia.
Phylum - Chordata.
Subphylum - Vertebrata.
Class - Mammalia.
Monotremes - Monotremes are Mammals which lay eggs instead of giving birth to live young and and nourish the young with milk from belly pores. The Monotremes are primitive egg-laying Mammals. Modern-day Monotremes include the Echidna (spiny ant-eater) and the Duck-Billed Platypus.
Marsupials - Marsupials are Mammals characterized by a Distinctive Pouch, called the Marsupium, in which females carry their young through early infancy. Some Marsupials include the Koala, Kangaroo and the Numbat. Majority of the Marsupials are found in Australia. There are about 334 Species of Marsupials
Placentals - Placental mammals are mammals whose young are born at a relatively advanced stage as compared to the Monotremes and Marsupials. Before birth, the young are nourished through a Placenta. The Placenta is a specialized embryonic organ that is attached the mother's uterus and delivers oxygen and nutrients to the young. Most Mammals are Placental Mammals, like Dogs, Cats, Humans etc. Scientifically, Placental Mammals are called Eutherians.
Herbivores - Herbivores are plant eaters and include Deer, Cow, Horse etc.
Carnivores - Carnivores are meat eaters and include Tiger, Lion etc.
Omnivores - Omnivores eat plants and meat. These include Bear, Badger, Dog etc.
Insectivores - Insectivores eat insects and include Anteaters, Pangolins etc.
1. Subclass Eutheria - Placental Mammals.
2. Subclass Metatheria - Marsupial Mammals.
3. Subclass Prototheria - Egg laying Mammals.
1. Epidermis - The Epidermis is typically ten to thirty cells thick, its main function being to provide a waterproof layer. Its outermost cells are constantly lost; its bottommost cells are constantly dividing and pushing upward.
2. Dermis - It is the middle layer. The Dermis is fifteen to forty times thicker than the Epidermis. The Dermis is made up of many components such as bony structures and blood vessels.
3. Hypodermis - The Hypodermis is made up of adipose tissue. Its job is to store lipids, and to provide cushioning and insulation. The thickness of this layer varies widely from Species to Species.
Weight - The Heaviest Mammal weighs 180 metric tons (200 short tons) or more in weight. The Lightest weighs 2 grams (0.07 oz).
Size - Mammals range in size from the 30–40 millimetre (1- to 1.5-inch) Bumblebee Bat to the 33-meter (108-foot) Blue Whale.
Mammals Distribution (geographical range & habitat)
Mammals are found all over the World, even Antarctica is no exception. Mammals live in many different Habitats like Deserts, Lakes, Mountains, Forests etc.
The evolution of Mammals within the Synapsid Lineage (mammal-like-reptiles) was a gradual process that took approximately 70 million years, beginning in the Mid-Permian. By the mid-Triassic, there were many Species that looked like Mammals, and the first True Mammals appeared in the early Jurassic. The earliest Mammals were tiny, Shrew-like Mammals. The earliest known Marsupial, 'Sinodelphys', appeared 125 million years ago in the early Cretaceous, around the same time as 'Eomaia', the first known 'Eutherian' (member of placentals' "parent" group); and the earliest known Monotreme, 'Teinolophos', appeared two million years later. After the Cretaceous-Tertiary extinction (due to natural disaster) wiped out the Non-Avian Dinosaurs (birds are generally regarded as the surviving dinosaurs) and several other Mammalian Groups, Placental and Marsupial Mammals diversified into many new forms and ecological niches throughout the Tertiary, by the end of which all modern orders had appeared. Some of the earliest-known mammals (the Mesozoic Era) include Eozostrodon, Deltatheridium, Jeholodens, Megazostrodon and Triconodon. The first true mammals appeared in the Late Triassic (ca. 200 million years ago), over 70 million years after the first Therapsids (type of Synapsid) and approximately 30 million years after the first Mammaliaformes.
In Placental Mammals, offspring are born as Juveniles. They are complete Animals having sex organs present but not reproductively functional. After several months or years, the sex organs develop further to maturity and the Animal becomes sexually mature. Most Female Mammals are only fertile during certain periods during their Estrous Cycle, at which point they are ready to mate. Individual Male and Female Mammals Meet and carry out copulation. For most Mammals, Males and Females exchange sexual partners throughout their adult lives. In most Mammals, fertilisation of the ovum (egg) takes place high in the Fallopian Tubes. The initial cell division occurs as the fertilised egg travels down the Fallopian Tubes. The egg become s a ball of cells called a 'Morula'. This 'Morula' separates into an inner cell mass and an outer layer of cells, at this stage it is called a 'Blastula'. The outer layer of cells is eventually called the 'Chorion' and the inner cell mass the 'Zygote'. While it travels down the Fallopian Tube the developing cell growth is supplied with nutrition from stored food in the egg, but in mammals this is in short supply and the developing Zygote soon needs a new source of nourishment.
Finishing its journey down the Fallopian Tubes, the Blastula enters the Uterine Cavity (the inside of the uterus). Within the Uterus, the Blastula connects with the Endometrium of the uterine wall in a variety of ways depending on which Species of Mammal. From this first contact the Placenta grows out of a complex of maternal material and embryonic tissues. There are at least 5 different forms, the Placenta can take in different Species of Mammals. Though each Species always takes the same form. The period of time during which the Foetus develops, dividing via Mitosis inside the female is known as Gestation. During this time, the Foetus receives all of its nutrition and oxygenated blood from the Female, filtered through the Placenta, which is attached to the Foetus' Abdomen via an Umbilical Cord. The Gestation Period, varies greatly from Species to Species. Once the Foetus is sufficiently developed, chemical signals start the process of birth, which begins with contractions of the Uterus and the Dilation of the Cervix. The Foetus then descends to the Cervix, where it is pushed out into the Vagina, and eventually out of the Female. The newborn typically begin respiration on its own shortly after birth. Not long after, the Placenta is passed as well. Most Mammals eat this, as it is a good source of protein and other vital nutrients needed for caring for the young. The end of the Umbilical Cord attached to the young’s abdomen eventually falls off on its own.
