2. A. Origin of Mammals The first mammals appeared about 230 million years ago, during the Triassic period.

3. A. Origin of Mammals Fossils indicate that they evolved from a now-extinct order of reptiles called therapsids

4. A. Origin of Mammals Therapsids were very abundant during the late Permian period (210-240 million years ago). Mammal-like reptiles and paramammals

5. A. Origin of Mammals Fossil remains of them, such as tooth and jaw fragments, show a mixture of reptile and mammalian characteristics. Mammalian and non-mammalian jaws. In the mammal configuration, the quadrate and articular bones are much smaller and form part of the middle ear. Note that in mammals the lower jaw consists of only the dentary bone.quadratearticular dentary

6. A. Origin of Mammals After the dinosaurs became extinct about 65 million years ago, this opened up many new habitats and resources to mammals, and mammals took over many of the ecological roles previously filled by dinosaurs.

7. B. Classification of Mammals Mammal species today number around 4,500. 22 orders are used in their classification

8. B. Classification of Mammals Mammals inhabit a wide range of habitats on land and in the water. They can survive in some of the coldest and hottest environments on Earth.

9. B. Classification of Mammals Adaptations such as blubber, large lungs, external ears, specialized teeth, and a large stomach containing symbiotic microorganisms that can break down cellulose in plants are just some of the many adaptations that have enabled mammals to inhabit such diverse environments.

10. B. Classification of Mammals Several important characteristics of mammals are listed below. 1. Endothermy -- Like birds, mammals produce body heat internally through metabolism 2. Hair -- All mammals have hair. The main function of hair is to insulate the body against heat loss. 3. 4-chambered heart with two completely separate ventricles.

11. B. Classification of Mammals 4. Milk – Female mammals produce milk to feed their offspring. Milk is a nutritious fluid that contains fats, protein, and sugars. It is produced by the mammary glands, which are modified sweat glands located on the thorax or abdomen. 5. Separate chest and abdominal cavities – in mammals, a dome-shaped muscle called the diaphragm divides the coelom into two parts: Thoracic and abdominopelvic cavities. 6. Extended parental care.

12. B. Classification of Mammals Mammals can be divided into three broad categories: 1. Monotremes  Egg-laying mammals EchidnaPlatypus

13. B. Classification of Mammals 2. Marsupial  Mammals are born early and complete their development in the mother’s pouch.

14. B. Classification of Mammals 3. Placental mammals  Nourish their young as they develop through a structure called the placenta.