Class Mammalia

A. General Characteristics

1. Body covered with hair, but reduced in some spp..

2. Integument with sweat, scent, sebaceous, and mammary glands.

3. Skeletal features include:

a. skull with

I. bony palate
II. middle ear with three ossicles (malleus, incus, and stapes)

b. seven cervical vertebrae
c. fused pelvic bones.

4. Mouth with diphyodont teeth (milk, or deciduous, teeth replaced by a permanent set of teeth); teeth in most spp. are heterodont (teeth with various structures and functions; lower jaw a single enlarged bone (dentary).

5. Movable eyelids and fleshy external ears

6. four limbs (reduced or absent in some spp.) adapted for many forms of locomotion.

7. Circulatory system of 4-chambered heart, non-nucleated RBC's, and biconcave RBC's.

8. Respiratory system of lungs with alveoli, and voice box (larynx); a secondary bony palate separates air and food passages; muscular diaphragm separates thoracic and abdominal cavities.

9. Excretory system of metanephric kidneys and ureters that usually open into a bladder.

10. Brain highly developed; 12 pairs of cranial nerves.

11. Strictly endothermic homeotherms.

12. Cloaca present only in monotremes (egg-laying mammals, such as duck-billed platypus).

13. Separate sexes; specialized reproductive and copulatory organs.

14. Internal fertilization; egg develops in a uterus with placental attachment (except in monotremes); fetal membranes (amnion, chorion, allantois); sex determination by heterogametic males (females are isogametic).

15. Young are nourished by milk from mammary glands.

B. Classification

Class Mammalia