Chordata Mammalia are vertebrates. There are over 4,500 different types of species of mammals.

Mammalian Characteristics

All mammals have three common characteristics that aren't found in any other kind of animal: 3 middle ear bones, mammary glands, and hair. The 3 middle ear bones are composed of the malleus (hammer), incus (anvil), and stapes (stirrup). Theses 3 bones aid in the conduction of vibrations from the eardrum to the inner ear. Mammals posses mammary glands, glands that produce milk. Because of mammals' presence of mammary glands, female mammals have a high parental investment, because they have to feed and nurture their young. They have hair which are made from keratin, a protein. Hair functions as insulation, sensory reception (like whiskers), and camouflage (like zebras, or any mammals colored like their environments).
[The three middle ear bones that all mammals share. ]

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Mammals are endothermic, have active metabolism, have a high metabolic rate, and contain a diaphragm that helps ventilate lungs. Their hair and layer of fat under skin help retain heat for the body. They are born by internal fertilization and the embryo develops inside the uterus of the females reproductive tract. Mammals contain a placenta which is the lining of the mothers uterus and extra embryonic membrane. It is used for nutrients to diffuse into the embryos blood. Marsupials are mammals that are born prematurely and finish their development outside the womb, frequently in a pouchlike structure. Kangaroos, wombats, and koalas are examples of marsupials.
They have larger brains capable for learning and have a differentiation of teeth that come in a variety of shapes and sizes. Mammals jaws are also remodeled to benefit there lifestyles.

This baby marsupial is finishing its developement in it's mothers pouch.(JS)
This baby marsupial is finishing its developement in it's mothers pouch.(JS)


The digestive system consists of the alimentary canal and various accessory glands that secrete juices throughout the ducts. A rhythmic movement of contraction to relaxation by smooth muscles to push foods along is called peristalsis. Sphincters close off the tubes regulation material that are able to pass between chambers. Accessory glands consist of salivary glands, pancreas, gall bladder, and the liver.

Food goes in through the mouth where mechanical (breaks down food chemically) and physical (chewing) digestion starts to break down food. The physical digestion is done with the use of teeth including canines, incisors, and molars, characteristics that is true for all mammals. Also, along with mechanical digestion in the mouth, is chemical digestion. For mammals, the salivary glands in the mouth are highly developed, creating an enzyme, amylase, that decomposes starch into glucose. From there it enters the pharynx which is the junction to the esophagus and the trachea (windpipe). The epiglottis blocks the trachea assuring the good goes down the esophagus which uses peristalsis to push the food down to the stomach. The stomach stores food and performs the preliminary digestion. Than the food goes through the pyloric sphincter into the small intestine, which does the major part of digestion and absorption. The food passes another sphincter into the large intestine where it reclaims most of the water. At the end of the large intestine is the rectum. The rectum stores the feces and is able to eliminate the feces as waste.

A basic diagram of a mammal's digestive system (JM)
A basic diagram of a mammal's digestive system (JM)

Mammals Senses

Senses are information that is transmitted through the nervous system in the form of nerve impulses or an active potential. Mammals have five senses. Hearing, Smelling, Touching, Seeing, and Tasting. Hearing is sensed in the ears. Sound waves from the air enter into the ear and are identified as certain sounds and the ear sends impulses to the brain to identify these sounds. The sense of smell is found in the nose. The olfactory receptors are found in the upper lining of the nasal cavity and are used to send impulses to the brain notifying it of a certain smell. Touching is identified through pressure, touch, stretching, and motion. Nerves send impulses to the brain of a feeling that are identified by the brain. Sight is found in the eyes. They absorb light and the photoreceptors send impulses to the nerves to send a transmission to the brain of the light the eye saw. Tasting is found in the mouth. Taste buds are used for tasting and are located on the tongue and mouth. Impulses are sent to the brain to identify the taste as being sweet, salty, sour, or bitter.


Ways of locomotion are swimming, crawling, walking, running, and even hopping. To move requires mammals to spend energy to overcome the forces of friction and gravity. The movement is based on contraction of muscles working against the skeleton. The skeleton supports and protects the animals body and are essential to movement. Calcium ions and regulatory proteins control the muscle contractions. Mammals often time must move greater distances and more often than other animals. This is aided by the fact that they possess a homeothermic, or warm-blooded, body, Furthermore, this is made possible by the the way mammals' limbs join the body. Mammals are capable of moving its legs backwards and forwards beneath its body (whereas a reptile, for example, has its legs stuck out to the side).


The lungs of mammals have a spongy texture and are honeycombed with a moist epithelium that functions as the respiratory surface. The air comes in through the mouth and nose. Here it is filtered by hairs, warmed, humidified and sampled for odors. The air goes to the pharynx and then the larynx and then to the trachea. The trachea branches into two bronchi and continue to get smaller until they are bronchioles. At this level they are alveoli. The alveoli are where the gas exchange occurs. Alveoli are wrapped in capillaries, which are one cell layer thick. The thinness of these capillaries facilitates the diffusion of oxygen into the blood and the diffusion of carbon dioxide out of the blood. The oxygen enters the body as the carbon dioxide leaves.The lungs are split into hundreds of thousands of alveoli. More alveoli in your lungs means greater surface area and greater intake of oxygen.

A close-up of respiration (BY)
A close-up of respiration (BY)


Mammals have a cardiovascular system. The heart pumps blood from the right atria to the right ventricle and then to the capillaries of the lungs. Here gas exchange occurs filling the blood with oxygen and having the carbon dioxide leave. The blood goes back to the heart where it is pumped through the left atria and then to the left ventricle and out to the body. The blood distributes the oxygen throughout the body and collect carbon dioxide as a waste. The blood goes back to the heart to restart the cycle. The 4 chambered heart keeps the oxygenated blood entirely separated from the deoxygenated blood. This separation makes the 4 chambered heart more advantageous and allows it to pump blood more efficiently.

This whole cardiac cycle or one pumping and filling of the heart is controlled by a rhythmic cycle from a sinoatrial node or the pacemaker. The SA node sets the rate and timing of the heart to contract.

Four Chambered Heart in Mammals (JAF)
Four Chambered Heart in Mammals (JAF)

Temperature balance

A mammals normal temperature is 36 degrees to 38 degrees Celsius. When the mammal needs heat it counteracts the heat loss using several adaptations. A high metabolic rate of endothermy produces large amounts of metabolic heat. Moving and shivering produce heat. Sometimes mitochondria will produce heat instead of ATP. Some mammals have brown fat located in the neck and shoulders that are used for rapid heat production. Insulation such as hair, fat layers, reduce flow of heat and lowers energy cost of keeping warm. When body is cold the heat from the arms and legs will go to the core of the body where all the main organs are located. When the body needs to cool, heat is removed. Some mammals use panting and most have sweat glands that promote evaporating cooling.

Evolution of Mammals

The ancestors of mammals are the therapsids who are part of the synapsid branch of the reptilian phylogeny. The structure of the legs, skull, jaws and teeth evolved slowly over long periods of times. As the Cenozoic era came in the beginning of the cretaceous extinctions mammals started to adapt into three major groups. The monotremes, egg-laying mammals, marsupials, mammals with pouches, and eutherian, placental mammals. [Monotremes are the most primitive mammals. There are three species of monotremes, the duck-billed platypus and two spiny anteaters. Marsupial young are born in an immature state. Females usually carry and nurse their young in pouches or pouch-like area on their abdomens.
.external image 1461_med.jpgArtist's impression of Megazostrodon, an early mammal


Chordates are phyla from the Deuterostone branch. They have four main characteristics. Notochord, dorsal, hollow nerve cord, pharyngeal slits, and muscular, post anal tail. The notochord, composed of large, fluid-filled cells, encases in fairly stiff fibrous tissue. It provides skeletal support throughout the animal, yet in most vertebrates, a complex, jointed skeleton develops leaving only remains of the notochord. The dorsal, hollow nerve cord develops from a plate of ectoderm that rolls into a tube located dorsal to the notochord. The nerve cord develops into the central nervous system, or the brain and spinal cord. The pharynx is posterior to the mouth and opens to the outside to the slits. The pharyngeal slits allow water to enter the mouth and exit without continuing through the entire digestive system. In some cases the slits and structures have been modified for gas exchange (aquatic vertebrates), jaw support, hearing, and other functions. The muscular, post anal tail is pretty much a tail extending posterior to the anus and contains elements of muscles and skeleton.

By: Jeremy Fransman

Review Question:
1) How does the the cardiovascular system work in mammals? Explain the circulation of blood through the body, as well as the function of blood.
2)Describe how mammals regulate body temperature.
3) Describe the respiratory system of the mammal.
4) What are the five senses in animals and what systems are associated with each?

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