Origin and Characteristics of Mammals

A. Origin of MammalsThe first mammals appeared about 230

million years ago, during the Triassic period.

A. Origin of MammalsFossils indicate that they evolved from a now-

extinct order of reptiles called therapsids

A. Origin of Mammals

Therapsids were very abundant during the late Permian period (210-240 million years ago).

Mammal-like reptiles and paramammals

A. Origin of MammalsFossil 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.

A. Origin of MammalsAfter 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.

B. Classification of MammalsMammal species today number around 4,500.

22 orders are used in their classification

B. Classification of MammalsMammals 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.

B. Classification of MammalsAdaptations 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.

B. Classification of MammalsSeveral important characteristics of

mammals are listed below.1. Endothermy -- Like birds, mammals produce

body heat internally through metabolism2. 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.

B. Classification of Mammals4. 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.

B. Classification of MammalsMammals can be divided into three broad

categories:1. Monotremes

Egg-laying mammals

Echidna Platypus

B. Classification of Mammals2. Marsupial

Mammals are born early and complete their development in the mother’s pouch.

B. Classification of Mammals3. Placental

mammals Nourish their

young as they develop through a structure called the placenta.