Earth Science: Biology – Animals – Mammals: Common Features
Mammals have spread successfully over the entire world, and have even conquered extreme habitats such as deserts and the Arctic. In spite of al external diversities, they have numerous characteristics in common.
Mammals are the most highly developed vertebrate animals. Their constant body temperature grants them a life largely independent of ambient temperatures. Depending on the species, the body temperature of mammals lies between 96.8 and 102.2°F (36 and 39°C). This is facilitated by a high food intake-in comparison to reptiles, for example-and an increased rate of metabolism.
In addition, they have temperature insulation, such as thick fur, to protect sensitive body organs. Mammals, such as whales or humans, where hair has been secondarily regressed, have an insulating layer of fat. A long digestive tract, dentition with four various types of teeth, and a powerful chewing musculature allow for the utilization of diverse food components.
The mode of nutrition in mammals ranges from pure plant, insect, and meat eaters to omnivores. Lung respiration, typical of mammals, together with an effective circulatory system, supplies the body cells efficiently with oxygen. The heart consists of two atria and two ventricles, which are completely separated from each other.
This prevents the mixing of oxygen-rich and oxygen-deficient blood. The red blood corpuscles do not have cell nuclei. This makes their shape more flexible and enables them to pass through the narrowest of capillaries.
Progeny
All mammals, except for the egg-laying monotremes, give birth to live young. During the pregnancy in higher mammals, the fetus is linked to the circulatory system of the female and is supplied with nutrients via the placenta and through the umbilical cord.
The exchange of oxygen and carbon dioxide also takes place via this route. Following the birth, the progeny is raised with a special dietary substance: the fat and nutrient-rich mother’s milk.
Milk is given off from special breast glands, which facilitate quick growth of the newborn. Breast-feeding also leads to the formation of a strong mother-child bond that is the basis of close social structures.
MARINE MAMMALS IN DANGER
Whales and dolphins are not only endangered by commercial whaling activities: An estimated 60,000 animals die each year in enormous drift nets of the general fishing industry. Furthermore, there is overfishing of the seas, which takes food away from large marine mammals. Increasing pollution of the oceans by environmental toxins further restricts the habitat of these animals. “Noise pollution” from military and commercial shipping interferes with the orientation capabilities of whales and may cause them to become deaf.