Animalia-Chordata - Mammalia

Chuck Norris, a prominent Mammal
Chuck Norris, a prominent Mammal

Diagnostic Characteristics of Mammals-
The class Mamalia, which contains about 5,400 species, is characterized as vertebrate animals which have sweat glands, mammary glands, hair, give birth to live young (with a few exceptions), are endothermic, and have a four chambered heart. Almost all mammals have seven neck bones as well (except sea cows and sloths) (SES 13). Mammary glands and the ability to produce milk are distinctly mammalian characteristics of females (ER). All mammals have a set of "milk teeth" known as baby teeth in human beings (SES 13). As a mammal gets older, it will lose its milk teeth and its adult teeth will come in (SES 13). The brains of mammals are generally larger than that of other animals of comparable size. While other creatures, such as reptiles, have conical and uniform teeth, mammals have several different types of teeth that are best suited for different tasks. They contain middle ear bones and a single-boned jaw (SES 12). Most mammals have a high metabolic rate that is supported by efficient respiratory and circulatory systems. Mammals diversified greatly after the cretaceous extinctions that took place 64 million years ago. Because it is so diverse, taxonomists have established 26 orders within this class (SES 12).

As seen in this picture, the Mammalian brain (in this case, the brain of a human) is larger than that of another animal. The Mammalian brain has a larger cerebral hemisphere. (DP)
As seen in this picture, the Mammalian brain (in this case, the brain of a human) is larger than that of another animal. The Mammalian brain has a larger cerebral hemisphere. (DP)

Acquiring and Digesting Food-
Mammals can be either carnivores, herbivores, or omnivores. Many species can tolerate a diet of diverse prey. Mammals can be grazers or hunters, and can endeavor to acquire food alone or in groups.
Mammals have a complex digestive system whose purpose is to break down food mechanically and chemically and to absorb the resulting nutrients into the bloodstream to nourish the cells of the body. This process starts at the mouth, where ingestion occurs and chemical digestion begins. When the food enters the oral cavity, saliva is excreted from the salivary glands and starts the process of chemical digestion using an enzyme, salivary amylase(ER), that can start breaking apart complex sugars. The oral cavity is also responsible for mechanical digestion. The teeth break up food in order to increase its surface area and allow for better absorption later on in the digestive process. Although chewing and swallowing foods are voluntary actions, nothing else in the process of digestion happens voluntarily (3 NK). By the process of peristalsis, the rythmic waves of contraction by smooth muscles in the wall of the canal, food is transported into the stomach, where it is broken down further chemically and mechanically. The nutrients of the food are absorbed into the bloodstream in the small intestine by small little appendages called villi (OZ), and the remaining waste is dried in the large intestine, where water is also reabsorbed (OZ), and eliminated during excretion.

Sensing the Environment-
Mammals have developed many diverse methods of acquiring information about their surroundings. Many mammals utilize senses such as sight, smell, hearing, touch, and taste. However, other, less traditional senses do exist. Echolocation is the use of sound made by the animal to "see" its environment. Bats commonly use echolocation to sense its environment. It releases a high-pitched sound with its vocal chords (too high pitched for humans to hear). The sound bounces off other objects and comes back to the bat. The bat then hears the sound waves returning to it, processes the sounds, and is able to sense those objects near it. (4) (JAC) Marine mammals such as dolphins and whales use echolocation too. Still others can sense the Earth's magnetic field and use that information to aid endeavors such as migration.

Mammals overcome the problem of locomotion with the utilization of limbs. Resembling arms, legs, fins, or wings, limbs make it possible for mammals to walk, swim, or fly. Some mammals have clawed limbs, which are useful in climbing, fighting, or gripping surfaces. Strong limbs allow for considerable dexterity, and enable the mammal to jump. Limbs like the one in the figure above are usually movable and tend to be able to rotate (6 BL).
The majority of mammals travel across land. This is partly made possible because of the way a mammals limbs join with the body. A mammal moves its legs backwards and forwards beneath its body. Mammals use tendons, a band of tough tissue that connects a muscle to a bone, and their backs for energy while walking and running to enhance their efficiency. Most terrestrial mammals can ump or leap, but certain animals use this ability much more than others. Leaping can occur from two legs, as in the money, four legs, as in the pronghorn, or a mixture of its four legs. For example a cat leaps using mostly its back legs, yet it gets some lift from its front legs. Some aquatic mammals, such as seals, move by crawling. This is effective, but it is often slow. (8) (BMB)

In order to perform gas exchange, mammals utilize a respiratory system that includes lungs. Gas exchange occurs at the lungs, which provide the large surface area, permeable membrane, and moist surface necessary for oxygen to diffuse into the circulatory system and for carbon dioxide to diffuse out. Mammalian lungs have a spongy texture, and are composed of every narrowing tube-like structures known as bronchioles that lead to air-filled sacs called alveoli. Alveoli are crisscrossed by capillaries, which bring in venous blood from the pulmonary artery and carry out oxygenated blood from the pulmonary vein (AR). Here, diffusion occurs as the blood comes in contact with the oxygen in the alveoli (AR). When molecules diffuse, they move away from a place where they are very concentrated to another place where they can be less concentrated. This is like emptying a crate of balls: the balls are all together inside the box (concentrated), but once the box is turned upside down, the balls bounce away from each other (less concentrated). If you imagine oxygen molecules as balls, there are many of them in the alveoli but not so many of them in the capillaries wrapped around the alveoli. The oxygen molecules will want to bounce out of the alveoli into the blood vessels, where they are more spread out. Alveoli are very efficient for the diffusion of oxygen into the capillaries because they allow for a larger surface area. Having a larger surface area means that there can be more capillaries wrapped around the alveoli, so more oxygen can diffuse into the blood (what I learned in sophomore year)[HZ] . As lungs are contained within the body, a pathway must exist to external air. This need is remedied by the upper respiratory tract, composed of the structures such as the nasal cavity, larynx, pharynx, and trachea, which provides a path for air to enter and exit the lungs.
Ventilation, also known as breathing, occurs when the diaphram and intercostal muscles contract. This increases the volume of the thoracic cavity. In order for pressure to remain constant, air rushes into the lungs from the environment. When the diaphram and intercostals relax, the volume of the thoracic cavity decreases and air rushes out of the lungs.
external image lungs.jpg
This diagram depicts the lungs, and labels all major parts. It highlights the alveoli sacks. The use of alveoli sacks in lungs increases the surface area, and allows more oxygen to be held. (7, GR)

Metabolic Waste Removal-

Matter that cannot be absorbed into the bloodstream is dried in the large intestine and is eliminated from the body via the anus by the process of defacation.


The mammalian circulatory system (ER). Blue represents oxygen poor blood and red represents oxygen rich blood.[1] Sarah Vlach

Mammals, being vertebrates, have a closed circulatory system that is often referred to as the cardiovascul ar system. The heart, which is the pumping mechanism (shown by the systemic circut) of the body, is four chambered. Blood, the medium in which nutrients are carried throughout the body, travels in arteries, veins, and capillaries. If all the blood vessels of the body were laid out in a straight line, they would reach out over one hundred thousand kilometers. The cardiovascular (heart) and pulmonary (lung) system work together to insure the best possible circulation. Deoxygenated (oxygen-poor) blood (blue in diagram) leaves the heart through the aorta, which is the main artery of the heart. An artery is responsible for carrying blood away from the heart and into the circulation system. The oxygen-poor blood then enters the lungs where gas exchange occurs between the lungs and the walls of the capillaries (very small blood vessels). Shown by the pulmonary circut changing from blue to purple to red. Once gas exchange occurs, the oxygen-poor blood becomes oxygen-rich blood. The oxygen-rich blood is then transported back to the heart through many veins. Veins are responsible for bringing oxygen-rich blood back to the heart. (Jesse Carmen) [2]

Self Protection-

Mammals possess many forms of self protection that aid in survival. Some species of mammals live in groups, which makes it more difficult for a predator to subdue any one member of the group. Individually, mammals may possess claws, antlers, horns, or poisons to aid in self defense. Species may also be especially agile in the hope of escaping the grasp of predators.As the snowshoe hair races to escape the grasp of the lynx.(SJB)(9)
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Another adaptation of mammals is their ability to strategically reason through defense. Humans are able to reason though complex defense systems and develop intuitive systems of protecting oneself. (RJS)
Osmotic Balance-
Mammals maintain an osmotic balance through the management of water in the body. When the amount of water in the body exceeds the necessary amount, excess water is eliminated by urination. When there is not enough water, a sense of thirst develops and the individual is compelled to seek out hydration.

Temperature Balance-
Mammals are endoderms, meaning that they produce their own body heat. This allows mammals to stay within certain boundaries temperature wise regardless of the outside temperature. In the large, mammals maintain body temperatures of within 36-38 degrees celcius. As the body temperature of mammals is normally warmer than that of the surroundings, mammals must constantly generate heat to counteract the loss of energy to the environment. Heat can be produced by a variety of methods, be it by mechanical motion of the muscles in the form of shivering or physical activity, or through cellular respiration. Many mammals have insulationary materials such as fur, blubber, or thick skin that helps reduce heat loss. Most marine mammals rely on blubber or thick skin on insulation, however, as hair loses much of its insulating power when wet. Some mammals also have developed adaptations that aid in cooling, such as sweating or the tendency to wallow in mud. Some mammals pant (for example dogs) to release extra body heat as well (SES 13).

Three Ways of Reproduction
There are three different ways that mammals reproduce. The first method is by laying eggs. The mammals that utilize this method are known as monotremes.(5) The offspring develops within the egg and hatches at an advanced stage of development. These offspring are fed on milk once hatched, unlike other hatched animals, such as birds, who are fed on caught or collected food. The milk is produced by the mother. This group of mammals includes the platypus and echidnas. One important fact to note is that reproduction is used to mark evolution; therefore many scientists consider monotremes to be the least evolved of all mammals. (10 Nangia) The second method by which mammals may reproduce is that utilized by Marsupials. Their young are born in an immature state and are develop after birth in a pouch. (5) These young are underdeveloped and therefore struggle to teat and start feeding. The pouch that contains the offspring is also where the teats of the mother are located; therefore the offspring can easily access its mother’s milk. This group of mammals includes koalas, kangaroos, opossums, and some gliders. Marsupials mark the next stage in animal reproductive evolution. (10 Nangia) The third type of reproduction is when the offspring is born at an advanced state. The mammals who reproduce in this way are called placental mammals. A lot of development occurs before birth as the offspring are nourished through an embryonic (early stage, before birth) organ called the placenta, which delivers nutrients and oxygen to the young (5). (RK) This final group includes the vast majority of all mammals. The placenta is the vital organ that allows for young to develop within their mother. It protects the offspring from the mother’s immune system. Because the offspring is composed of different cells than the mother, the mother’s immune system naturally attacks the offspring. The placenta is composed of several layers of material, and is rich in blood vessels that carry nutrients to the fetus. Because the offspring is born at a highly developed stage, these mammals have a very long gestation period (pregnancy). This long gestation period allows for many mammals to run, walk, or see just a few hours after they are born. Placental mammals include rabbits, bats, cows, elephants, humans, and a large multitude of others. (10 Nangia)


The species of mammals are known to live in almost every habitat: aquatic and terrestrial environments, and in every biome: rainforests, deserts, etc. A great number of land mammals are able to live aquatically and in fact live near rivers, coastlines, and lakes. Some examples of these partially aquatic animals are otters, walruses, and sea lions. Suprisingly enough, there are even mammals that completely reside in water. Whales and dolphins are examples, and are found in all oceans. (11 DJ)

The Evolution Of Man:



1) Mammalia can be either carnivores, herbivores, or omnivores, but their digestive systems are all similar. Describe how mammlaia digest their food. (HS)
2) What are the 3 methods of mammal reproduction, and what does each involve? (VM)
3) Briefly describe the methods used by mammals to regulate temperature. (SS)

Edits by:
Jesse Carmen
Sarah Vlach
Ethan Richman
Omer Zaidi
Josh Czik
Rachel Kornetsky
Becca Levenson
Grace Rehnquist
Brittany Marcus-Blank
Sam Blatchford
Meru Nangia
Hilary Stepansky
Hanna Zhu
Sarah Schwarzschild

Works Cited

Campbell, Neil, and Jane Reece. Biology. Sixth ed. Ed. Beth Wilbur. Boston: Benjamin Cummings, 2002. 702, 874, 859-866, 889-897, 930-931.

Marieb, Elaine N. Human Anatomy and Physiology. Sixth Ed. San Francisco, CA: Benjamin Cummings, 2004. [2]

(3) Farabee, MJ. "The Digestive System." EMC. 7 Dec. 2008
[4] "Bat Radar - Echolocation - Vision & Habitat." Bat Radar - Echolocation - Vision - Habitat of Bats. 2006. 7 Dec. 2008 <>.
(5) Col, Jeananda."All About Mammals." Enchanted Learning. 1998. 7 Dec. 2008 <>.
(6)"mammal." Encyclopædia Britannica. 2008. Encyclopædia Britannica Online. 07 Dec. 2008 <>.
(7) "The Excretory System." The Human Body Systems Tour. 25 Nov. 2006. 7 Dec. 2008 <>.
(8) "Locomotion." Earth-Life Web Search Engine. 29 Sept. 2008. Earth-Life Web Productions. 7 Dec. 2008 <>.

(10) Ramel, Gordon. "The Placental Mammal and Reproduction." Reproduction In Mammals. 29 Sept. 2008. Earth-Life Web Productions. 8 Dec. 2008 <>.
(11)Wund, M. "Mammalia." Animal Diversity Web. University of Michigan. 17 Dec. 2008
(12) "The Characteristics of Mammals." Mammals. 18 Dec. 2008. <>
(13) "All About Mammals." 18 Dec. 2008. <>