Unit 7: Vertebrates                                                      1   2   3   4   5   6

2. Mammals

There are about 5,700 species of mammals.

They appeared 200 million years ago.

They evolved from a group of reptiles that developed hair

and capacity for feeding their calves with milk that themselves produced.

a) Habitat

     They are terrestrial tetrapods.

Some are aquatic (e.g. dolphins) and only one group can fly (bats)

b) Morphological characteristics

- They have four limbs. These extremities are adapted to different ways

         to move and can be wings, legs or fins.

- Their body is divided into: head, trunk and tail.

         The head is joined to the trunk by the neck. 

- Their skin is covered by hairs. They protect of heat loss.

- They have several types of glands: sweat glands, sebaceous glands

         and mammary glands.

c) Vital functions:

     Nutrition:

             The digestive system is complete. They have mouth

             with teeth and lips (to suction).

        Teeth have different shape depending on the kind of feeding

        the animal has.

        Anus opens outside directly.

Mammals breathe through lungs.

Interaction

    They have a well developed brain and sense organs:

    eyes (with eyelids), ears (with auricles), taste, smell and touch.

They are homeotherms (warm-blooded). This means that they can keep their body temperature constant.

Reproduction:

Fertilisation is internal.

They are viviparous. Young grow in the mother’s womb (uterus).

Mammals care young and females feed them with milk produced in their mammary glands.

d) Classification:

- Monotremes

       They are oviparous.

They have a beak without teeth.

- Marsupials

        They are viviparous but calves birth very immature and

       have to complete their development inside the mother’s pouch

       (marsupium).

- Placentals

     Young develop completely inside the mother’s uterus.

     Embryo is connected to the female by the placenta.

2.1. Answer the questions about mammal jaws:

a. Indicate, in each picture, the different types of teeth:

    - Incisors (colour them in yellow)

    - Canines (colour them in red)

    - Molars (colour them in blue).

b. What type of tooth is more developed in every case?

c. We can deduce by the type of dentition, what kind of food they take. Try to identify what of the skulls belong to a carnivorous, to an herbivorous and to an omnivorous.

2.2. Listen and indicate if the described characteristic belongs to: