Mammals

Characteristics of Mammals

1. 3 Middle Ear Bones – malleus, incus, and stapes (hammer, anvil, and stirrup) the first two derived from the ancestral jaw.

2. Hair – composed of keratin for insulation, sensation, appearance, and protection. (other keratinized structures – horns, antlers,

3. Mammary Glands – modified sweat glands that, in females, produce milk to nourish their offspring.

Other important characteristics include highly differentiated teeth, 2 sets of teeth, single lower jaw bone, 4 chambered heart, secondary palate, muscular diaphragm, highly developed brain, endothermy and homeothermy, separate sexes (XX or XY), and internal fertilization.

Mammalian Teeth

Heterodont teeth – different types of teeth

2 Sets of teeth - Diphyodont Dental Formula Diastema Carnassial apparatus1. Incisors chisel shaped for

gnawing and nipping (1 root)2. Canines long conical for

catching, killing, and tearing (1 root)

3. Premolars and Molars broad for chewing (1-2 or 2-3 roots)

Mammalian Glands

Glands are an epidermal tissue that secrete substances.

1. Sebaceous – secrete oil for waterproofing.

2. Sudoriferous – sweat for evaporative cooling and elimination of waste.

3. Scent – secrete pheromones for defense, sex recognition, and territorial behavior.

Mammalian Classification

1. Prototheria (Monotremes) - are oviparous (Egg-laying).

2. Metatheria (Marsupials) – are viviporous with a short gestation, further development occurring in a pouch. Doubled reproductive features in females & males.

3. Eutheria (Placentals) – are viviparous with a long gestation.

Terrestrial Placental Orders

1. Order Artiodactyla

2. Order Carnivora

3. Order Insectivora

4. Order Lagomorpha

5. Order Perissodactyla

6. Order Rodentia

7. Order Chiroptera

8. Order Primates

9. Order Edentata (Xenartha)

10. Order Proboscidea

Order Artiodactyla(Even Toed Ungulates) st

Ungulates walk on their toes. Most are specialized for

cursorial locomotion with long hoofed legs, and have diversified as the Perssodactyls have declined.

Number of teeth is variable but they have a diastema.

Males often sport antlers or horns.

Deer, Sheep, Javelina, Antelope, Cows, Hippopotamuses, Camels, Giraffes

Order Carnivora st

Although not all current carnivora are carnivorous, the ancestors were meat eaters.

Recognizable carnassial apparatus for shearing meat and tendons (between the 4th upper premolar and 1st lower molar), keen senses, and large brain.

3 upper and 3 lower incisors. Dogs, Cats, Bears,

Raccoons,

Order Insectivora

Third largest order of mammals and possibly the most primitive group (mesozoic mammals are rather shrew-like).

Moles and Shrews

Order Lagomorpha st

Resemble large rodents with short tails.

Flaps of skin can close behind the incisors and close the nostrils.

2 upper incisors, one behind the other.

(2/1, 0/0, … 4/4) Fenestrated skull Rabbits

Order Perissodactyla(Odd Toed Ungulates)

Horses, Rhinoceroses, Zebras

Feeding Adaptations

Herbivorous mammals have special adaptations for digesting cellulose.

1. Perissodactyls, lagomorphs, and rodents have a cecum or fermentation pouch between the small and large intestine. In lagomorphs droppings are re-eaten.

2. Artiodactyla are ruminants with the first three chambers of their stomach are storage and fermentation chambers. Food is regurgitated and chewed.

Order Rodentia st

Largest order of mammals (40% of mammal species).

Individual upper and lower incisors that are rootless and grow throughout life for a gnawing life style.

(2/1, 0/0, 3/2, 2-3/3)

Squirrels, Chipmunks, Rats, Mice, Beavers, and Porcupines

Being Warmblooded

Endothermy – the generation of internal heat Homeothermy – the maintenance of constant

temperature

Cold Weather Adaptations

Winter Sleep – the organism is less active, alert, and easily aroused (Bears and raccoons).

Hibernation – the organism slows metabolism, and heart and respiratory rates (monotremes, and some insectivora, rodentia, and chiroptera).

Order Chiroptera

Second largest order of mammals.

Bats

Order Primates

Lemurs, Tarsiers, Monkeys, Gibbons, and Apes

Order Edentata

Incisors and canines absent.

Armadillos

Didelphimorpha

American marsupials

Order Proboscidea

Elephants

Aquatic Placental Orders

1. Order Carnivora – Otters, Weasels, Seals, Walruses, Sea Lions

2. Order Cetacea – Whales, Dolphins, Porpoises

3. Order Sirenia - Manatees