MODOULE 9: CLASS MAMMALS
9.1. Module Objectives
At the end of this module the learner will be able to:
1.State the characteristics of the class Mammalia
2.State the Orders of the Mammalia
3.Describe the characteristics of the members of the various orders of Mammalia
9.2. Introduction
There are approximately 4500 species of mammals. Examples of mammals are dogs, cats, goats, rats, seals, whales, and humans. Mammals evolved from mammal-like reptiles called therapsids in the triassic period.
Figure Examples of mammals
9.3.Basic characteristics of Mammals.
Some of the basic characteristics of Mammals are:
9.3.1. Temperature control
Mammals are endothermic. That means they can maintain body temperature internally, without any external help. The picture on this slide shows hair covering the body of a Mammal.
The body of Mammals is covered by hair, made up of keratin. The hair helps in maintaining body temperature.
Figure 2 Hair on a mammal
9.3.2. Reproduction
Most mammals possess placenta ( an organ that nourishes the growing fetus) and give birth to live young.
Mammals have mammary glands to produce milk for offspring.
All mammals show parental care of offspring.
The picture (a) shows a placenta connected to the body of the mother. While Picture on this slide shows a baby feeding the mammary gland of the mother.
Figure 3 Placenta in a mammal
Figure 4 Mammary Gland
9.3.3. Control and coordination
Mammals have the most complex control and coordinating system comprising of the nervous system, endocrine system, sensory system.
9.3.4. Nutrition
Mammals have differentiated teeth, Heterodont dentition. For example man has four different sets of teeth namely incisors, canine molars and premolars. This feature allows mammals to feed on diverse types of food.
9.3.2. Respiration
Mammals have efficient respiratory system comprising of the diaphragm, and the lungs
Mammals have an effecient circulatory system comprising of the closed, double blood circulatory system with a four-chambered heart and the lymphatic system.
9.4. Types of Mammals.
Generally mammals are classified into three groups. Namely.
9.4.1. Monotremes
9.4.2. Marsupials
9.4.3. Placental
9.4.1. Monotremes
The Monetremes evolved directly from the Reptiles. This group includes the platypuses and echidnas (spiny anteaters).
Basic characteristics of Monotremes mammals
Some of the basic characteristics of Monotremes are
1.Males of Monotremes have claoca
2.Monotremes are the only group of Mammals that lay eggs (similar to that of Reptiles))
3.Monotremes have mammary glands to feed young ones.
4.Monotremes takes care of their young ones, feeds young ones after hatching.
Figure 5 Monotremes- Platypus
Figure 6 Monotremes- Echidna
9.4.2. Marsupials
The marsupials include kangaroos and koalas. Mostly found in Australia and New Zealand.
Basic characteristics of the Marsupial mammals
Some of the basic characteristics of the marsupials are:
Figure 7 Marsupials- Kangaroo
9.4.3. Placental Mammals.
Basic characteristics of Placental mammals.
Some of the basic characteristics of placental mammals are:
1.Embryos of placental mammals develop in the uterus.
2.The developing fetus of placental mammals are connected to the mother via the placenta. The placenta is used for feeding the developing fetus (exchange of gases, waste and nutrients). It is usually disposed after birth.
Figure 7 Placenta
9.5. Module summary
You have the following from this module:
1. Mammals are the most advanced class of the vertebrates. This class includes, man.
2.The basic feature of this class is the presence of mammary gland.
3.Mammary gland produces milk for feeding the young.
4.Mammal’s body is covered by hair.
5.Mammals have well developed coordinating and control system, nervous system, endocrine system, muscular system and the sensory system.
6.The mammals are classified into three groups, the monotremes( lay eggs), the marsupilals( lack placenta, give birth to young one and nurse it in a pouch}, and the placentas ( produce placenta, an organ that feeds the developing fetus).