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Section 12.6 Mammals.

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1 Section 12.6 Mammals

2 The Rise of Mammals The ancestor of modern mammals appear to have been reptiles called therapsids which lived 240 million years ago Therapsids had teeth, a skull, and limbs similar to modern day mammals Mammals remained small and uncommon until the Cretaceous extinction which saw the end of the dinosaurs After this extinction mammals underwent extensive differentiation As of today there are about 4,500 living species of mammals

3 Rise of Mammals As mammals diversified in the Cenozoic many changes occurred and as of today mammals are divided among three groups Monotremes Marsupials Eutherians

4 Monotremes There are only three living species: Are egg laying mammals
Duck-billed platypus 2 species of Echindas One found in Australia the other in New Guinea Are egg laying mammals Eggs are laid and warmed by the parent When hatched parent nourishes with milk secreted by a gland into the fur This is as they lack nipples

5 Marsupials Include animals such as
Kangaroos, opossums, bandicoots, and koalas Young are born in a extremely immature condition and undergo further development in their mothers pouch In the pouch suckle on their mother’s nipple for milk for nourishment

6 Eutherian Are placental mammals
Young develop in mother’s uterus Are nourished via the umbilical cords connection to the placenta Compared to marsupials have much longer periods of pregnancy Young are born with varying degrees of maturity which dictates length of dependence on their mother E.g. whales have to swim right away, humans are born naked and helpless Most mammals are in this group About 95% Are divided among various orders as compared to monotremes and marsupials who are their own order

7 Major Orders of Mammals
*See page of textbook*

8 Major Orders of Mammals

9 Major Order of Mammals

10 Major Orders of Mammals

11 This diagram shows the 3 groups of mammals
Note how the eutherians are placed into four clades This is done based on a current hypothesis for the evolutionary relationships among the eutherian orders This is hypothesis is based on molecular systematics Molecular systematics is a relatively new field. Sequences of genetic code analyzed by high-speed computers allow systematists to test evolutionary relationships at their most basic level. Studies of mitochondrial DNA (mtDNA) sequences have already revealed some astonishing things about the evolutionary interrelationships of many groups of creatures, from humans to whales to sharks. From:

12 Closer Look at order Primates
The classification of this order is complex and under constant review Part because humans are in this order Also because getting more and more new fossils that deem review For some more details read through section in text on page Diagram shows one of the present classification systems

13 General Characteristics of Mammals
Here are key characteristics for an animal to be a mammal: Warm-blooded Are air-breathing, with diaphragm separating the lungs from the general body cavity 4 chambered heart Skin is covered with hair (could be bristles, wools, scales or fur) and most have sweat glands Fat layers Teeth that are fixed into sockets in the jawbone 4 limbs, limbs often pentadactyl (with five toes), and endoskeleton Middle ear Well developed brain Are viviparous (bear live young) {only exception are the monotremes} One of most distinctive features is the presence of the mammary gland (hence the name mammal from mammary)

14 Warm-Blooded Being warm blooded makes mammals endothermic
To be endothermic means an active metabolism To meat this metabolism mammals have efficient cardiovascular systems 4 chambered heart keeps oxygenated and deoxygenated blood from mixing Lungs with extensive internal folding improve surface area, making more efficient gas exchange

15 Hair, Sweat Glands and Fat Layers
Hair, sweat glands and fat layers help in maintaining body temperature Hair and fat help insulate to keep heat Sweat glands make sweat to cool down (note not all mammals have sweat glands) Hair can also help provide camouflage depending on the colouration Amount of hair and exact type vary among species as some hair has become specialized E.g. porcupine guard hair makes the quills, one of its defense mechanisms Hair is made of the protein keratin Keratin also makes other structures such as: horns, toes, hooves, fingernails, claws, and antlers

16 Teeth Mammals can have various types of teeth and arrangements of such teeth Based on the type and their arrangement reveal if the animal is an omnivore, carnivore, herbivore or insectivore Teeth types are as follows Incisors Canines Premolars (bicuspids) Molars (tricuspids) The types of teeth appear in the order given from the front to the back of the mouth on both sides in the upper and lower jaw (if the animal happens to have all 4 types) Another thing is the teeth in both jaws match up, unlike those of reptiles This aids in chewing

17 Types of Teeth and their Roles
Incisors Used for biting and tearing In elephants the upper incisors have developed into tusks Canines Help in holding and piercing prey In walrus are called tusks Premolars and Molars Used for chopping and grinding food

18 Teeth and Diet Based on the teeth an animal has it can help us determine their diet E.g. cows chew grass and thus have largely incisors and molars Also based on animals diet will influence what their digestive system is like Note how herbivores digestive system larger as this is needed to break down food with high cellulose content

19 Showing how Teeth and Jaws Vary Based on Animals Diet

20 Endoskeleton Having an endoskeleton gives 3 advantages over animals with an exoskeleton Can grow continuously without moulting phase Do not have to divert metabolic energy to make new skeleton Do not have vulnerable period while new exoskeleton forms

21 Skeleton and Limbs With well developed muscles and bones, particularly where they are jointed the skeleton is very flexible Structure and location of limbs help permit ease of motion and speed The pectoral and pelvic girdles have been modified to support and accommodate the location of the limbs Limbs have modified and adapted for many mammals based on their environment

22 Pentadactyl Limbs The variation of limbs being pentadactyl (have five toes) is due to adaptations to running For example for some the central toe has become the most important and the total number of toes has reduced We will also look at some other limb modifications Note regardless of the modification/adaptation the number and organization of limb bones have remained relatively constant

23 Limb Modifications Modification for flight:
Elongated fingers Between fingers a web of membranous skin stretches that extends to the hind limb The only true flying mammals are bats

24 Limb Modification For aquatic mammals Forelimbs have become flippers
In some hind limbs also flippers (seals, sea lions) and in others they lack hind limbs (whales, dolphins) Those without hind limbs have well developed tails

25 Limb Modification For upright mammals
Hind limbs are limited to movement Has allowed forelimbs to be free for specialized functions such as grasping and manipulating objects

26 Middle Ear Most obvious is allows for hearing
Hearing is very vital for survival Especially to those using echolocation (e.g. bats)

27 Developed Brain Require developed brain to enable the learning of various behaviour patterns Has been a key in mammals success Most notably in humans as it is what has made us so successful

28 Mammary Gland Produces milk that is used to nourish young
Young get milk from their mother by suckling on a nipple

29 Reproduction For breeding some mammals have complex behaviours/courtships Fertilization is internal Mammals are viviparious as they give birth to live young Monotremes are the exception

30 Home Work Read pages 465-475 Answer questions 1-6 page 467

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