It's sad to think that one day, the planet Earth may be gone. This is despite our best efforts to save her. The good news is that provided we all work together, we can preserve the status quo on our beautiful blue world, for centuries to come - maybe even catalogue the makeup of our beautiful home. Provided that is we heed the warnings nature is sending us, such as global warming and other pollutions upsetting nature's balance.
Let the animals enjoy the Earth
Food for thought: As an intelligent species, we are in a (possibly unique) position to catalogue and preserve all life on earth. With our knowledge of genetics and DNA, we might one day be able to restore the life we know today, to another planet, Jurassic Park style. Anything is possible.
Mammals are the class of vertebrate animals characterized by the presence of mammary glands, which in females produce milk for the nourishment of young; the presence of hair or fur; and endothermic or "warm-blooded" bodies. The brain regulates endothermic and circulatory systems, including a four-chambered heart. Mammals encompass some 5,500 species, distributed in about 1,200 genera, 152 families and up to 46 orders, though this varies with the classification scheme.
Phylogenetically, Mammalia is defined as all descendants of the most recent common ancestor of monotremes (e.g., echidnas and platypuses) and therian mammals (marsupials and placentals).
The vast majority of mammals have seven cervical vertebrae (neck bones), including bats, giraffes, whales, and humans. The few exceptions include the manatee and the two-toed sloth, which each have only six cervical vertebrae, and the three-toed sloth with nine cervical vertebrae.
Mammals have three bones in each ear and one (the dentary) on each side of the lower jaw; all other vertebrates with ears have one bone (the stapes) in the ear and at least three on each side of the jaw. A group of therapsids called cynodonts had three bones in the jaw, but the main jaw joint was the dentary and the other bones conducted sound. The extra jaw bones of other vertebrates are thought to be homologous with the malleus and incus of the mammal ear.
The mammalian heart has 4 chambers. There are 2 different heart chambers, one being for transporting the blood and the other for recieving the blood. The right atrium pumps blood to the right ventricle, and the left atrium pumps blood into the left ventricle. This blood is then pumped from the atrium into the second chamber called the ventricle. The ventricles are much larger than the atria and their thick, muscular walls are used to forcefully pump the blood from the heart to the body and lungs.
Head and brain
All mammalian brains possess a neocortex. This brain region is unique to mammals.
Mammals have integumentary systems made up of three layers: the outermost epidermis, the dermis, and the hypodermis. This characteristic is not unique to mammals, but is found in all vertebrates
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. 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. 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.
No mammals have hair that is naturally blue or green in color. Some cetaceans, along with the mandrills appear to have shades of blue skin. Many mammals are indicated as having blue hair or fur, but in all cases, it will be found to be a shade of grey. The two-toed sloth can seem to have green fur, but this color is caused by algae growths.
Most mammals give birth to live young, but a few (the monotremes) lay eggs. Live birth also occurs in some non-mammalian species, such as guppies and hammerhead sharks; thus it is not a distinguishing characteristic of mammals. Although all mammals are endothermic, so are birds, and so this too is not a defining feature.
A characteristic of mammals is that they have mammary glands, a defining feature present only in mammals. The monotremes branched from other mammals early on, and do not have nipples, but they do have mammary glands. Most mammals are terrestrial, but some are aquatic, including sirenia (manatees and dugongs) and the cetaceans (dolphins and whales). Whales are the largest of all animals. There are semi-aquatic species such as seals which come to land to breed but spend most of the time in water.
True flight has evolved only once in mammals, the bats; mammals such as flying squirrels and flying lemurs are actually gliding animals.
Mammals belong among the amniotes, and in particular to a group called the synapsids, distinguished by the shape of their skulls, in particular the presence of a single hole on each side where jaw muscles attach, called temporal fenestra. In comparison, dinosaurs, birds, and most reptiles are diapsids, with two temporal fenestrae on each side of the skull; and turtles, with no temporal fenestra, are anapsids.
From early synapsids came the first mammal precursors, therapsids, and more specifically the eucynodonts, 220 million years ago (mya) during the Triassic period.
Pre-mammalian ears began evolving in the late Permian to early Triassic to their current state, as three tiny bones (incus, malleus, and stapes) inside the skull; accompanied by the transformation of the lower jaw into a single bone. Other animals, including reptiles and pre-mammalian synapsids and therapsids, have several bones in the lower jaw, some of which are used for hearing; and a single ear-bone in the skull, the stapes. This transition is evidence of mammalian evolution from reptilian beginnings: from a single ear bone, and several lower jaw bones (for example the sailback pelycosaur, Dimetrodon) to progressively smaller "hearing jaw bones" (for example the cynodont, Probainognathus), and finally (possibly with Morganucodon, but definitely with Hadrocodium), true mammals with three ear bones in the skull and a single lower jaw bone. Hence pelycosaurs and cynodonts are sometimes called "mammal-like reptiles", but this is strictly incorrect as these two are not reptiles but synapsids.
During the Mesozoic Period, mammals diversified into four main groups: multituberculates (Allotherium), monotremes, marsupials, and placentals. Multituberculates went extinct during the Oligocene, about 30 million years ago, but the three other mammal groups are all represented today. Most early mammals remained small and shrew-like throughout the Mesozoic, but rapidly developed into larger more diverse forms following the Cretaceous-Tertiary extinction event 65 mya.
The names "Prototheria", "Metatheria" and "Eutheria" expressed the theory that Placentalia were descendants of Marsupialia, which were in turn descendants of Monotremata, but this theory has been refuted. However, Eutheria and Metatheria are often used in paleontology, especially with regards to mammals of the Mesozoic.
A series of vertebrate animal lineages is listed below. all of these groups predate mammals, and are close relatives.
Mammals appear in the mid-Jurassic period, and persist to the present (as Monotremes, Metatheria, and Eutheria)
Please use the Index below to navigate the Animal Kingdom:-
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