What is a Mammal?
Definition: have hair and the ability to nourish their young with milk, all mammals breathe air, have four-chambered hearts, and are endotherms that generate their body heat internally.
Definition: have hair and the ability to nourish their young with milk, all mammals breathe air, have four-chambered hearts, and are endotherms that generate their body heat internally.
Body Plan:
A lower jaw consisting of a large, teeth-bearing bone connected directly to the skull by a joint; complex teeth that are replaced just once in a lifetime; and distinctive features of the limbs and the backbone. Mammals are descended from ancient reptiles. Feeding: Because of its high metabolic rate, a mammal must eat nearly 10 times as much food as a reptile of the same size to maintain homeostasis. Mammals include herbivores, carnivores, and omnivores. As mammals evolved the form and function of their jaws and teeth became adapted to eat other foods other than insects. Circulation: Birds have four-chambered hearts and two separate circulatory loops. The right side of the heart receives oxygen-poor blood from all over the body and pumps it to the lungs. After picking up oxygen in the lungs, blood returns to the left side of the heart. This oxygen-rich blood is then pumped through blood vessels to the rest of the body. Respiration: All mammals, even those that live in water, use lungs to breathe. At the same time, a powerful muscle called the diaphragm pulls the bottom of the chest cavity downward, which further increases its volume. As a result, air is pulled into the lungs. When the chest muscles lower the rid cage and the diaphragm relaxes, the volume of the chest cavity decreases. This action pushes air out of the lungs. |
Excretion:
Mammals have highly developed kidneys that help control the composition of body fluids. Their kidneys extract nitrogenous wastes from the blood in the form of urea. Urea, other wastes, and water combine to form urine. The kidneys of mammals help maintain homeostasis by filtering urea from blood, as well as by excreting excess water or retaining needed water. Because they are so efficient at controlling and stabilizing the amount of water in the body, the kidneys enable mammals to live in many habitats. Response: Mammals have the most highly developed brains of any animals. The brain consists of three main parts: the cerebrum, the cerebellum, and the medulla oblongata. Reproduction:
Mammals reproduce by internal fertilization. |
Monotremes
Monotremes lay eggs. They are also grouped in a single order. They share two notable characteristics with reptiles. In monotremes, the digestive, reproductive, and urinary systems all open into a cloaca that is similar to that of the reptiles. Their reproduction also resembles that of reptiles. Unlike young reptiles, their young are nourished by their mother's milk, which they like from pores on the surface of her abdomen.
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Marsupials
Marsupials bear live young, but at a very early stage of development. They are also split into several different orders. They bear living young that usually complete their development in an external pouch.
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Placental
This group gets its name from an internal structure called the placenta, which is formed when the embryo's tissues join with tissues from within the mother's body. In placental mammals, nutrients, oxygen, carbon dioxide, and wastes are exchanged efficiently between embryo and mother through the placenta. The placenta allows the embryo to develop for a much longer time inside the mother. After birth, most care for their young and provide them with nourishment by nursing.
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