MAMMALS:
Definition: Most mammal young develop internally and after birth are nursed on milk. A few hatch eggs. Mammals have hair or fur at some time during their lives.
Characteristics:
Mammals have the most complex brains of all the vertebrates. Mammals generally have the most highly developed teeth. The senses of hearing and smelling are typically well developed. Mammals have four-chambered hearts.
After birth, the young continue to recieve maternal care. The milk from most mammary glands is about 85% water. The remaining 15% is composed of carbohydrates, fats, proteins, vitamins, and minerals. Although the milk of all mammals contains the same nutrients, the proportions of nutrients vary from species to species. The milk of each species is ideally suited for the nutrition needed by its young. They recieve nutrition from the mammary glands from which they obtain the mother's milk. The mother teaches the young to find their own food, and protects them from enemies.
Placentals:
-There are 17 orders of placental mammals. Some of the groups are very large, and can have up to one-hundred different species.
-Major orders of mammal are: rodents, rodent-like animals, bats, and, mammals that live in the water.
-A few examples of placental mammals are: beaver, jack rabbit, and tiger.
Marsupials:
-Fertilization is internal in marsupials.
-Development of embryos begins in the mothers uterus.
-A few examples of marsupials are: Red Kangaroo, Koala, Mole, and opposum. Opposums are the only North American marsupials.
Digestion:
-Plant matter is much harder to digest than animal matter because the cells of plants are surrounded by walls of cellulose. Mammals do not have the digestive enzymes necessary to break down cellulose. However, microorganisms living in the digestive tracts of ungulates can digest cellulose. The microorganisms obtain their nourishment from the cellulose and make the contents of the cells available to the ungulates.
-Some ungulates, called ruminants, have several compartments to their stomachs. Food that is partially digested is regurgitated, rechewed, and then passed into another common compartment.
Reproduction:
Mammals reproduce by internal fertilization. With few exceptions, mammals do not lay eggs. In most mammals the embryo develops in a muscular organ called the uterus. Some mammals develop inside an egg and others develop in a pouch outside the mother's body. The mammal class is divided into three groups based on their different methods of reproduction. The groups are:
- The Monotremes: animals that lay eggs and incubate them in a bird-like fashion
- The marsupials: pouched mammals. The marsupials leave the mother's uterus and crawl to the pouch. There they attach to the nipples and complete their development.
- The placentals: The young live inside the womb until mature enough to come out.
Body parts/Structure:
-The Structural features of the placenta are uniquely equipped to allow for the efficient exchange of nutrients and waste materials.
For More Info:
http://www.waynecounty.com/rougeriver/wildlife/creature/mammals.html
