1. Mammals!!!
NB #159
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2. Mammal Taxonomy Kingdom: Animalia Phylum: Chordata Subphylum: Craniata
Infraphylum: Vertebrata
Class: Mammalia

3. Evolution of Mammals Began evolving 320 mya
“Age of Mammals” began 70 mya
Flourished after the extinction of many reptiles
The early group of mammal ancestors were part of the “synapsid branch”
Large sails- raised body temperature at night
Lacked hair
Egg layers (oviparous)
Either herbivores or carnivores
Large anterior teeth
Gap between these teeth and the posterior teeth allowed the jaw to close
Arched palate- strengthened the upper jaw and allowed air to pass over prey in the mouth

4. Evolution of Mammals Therapsids
Predators- teeth mostly in the front of the mouth to hold & tear prey
Herbivores- large space separating anterior & posterior teeth
Posterior teeth specialized to shred plants
Hindlimbs directly beneath body
Changes in ribs allowed for mammalian breathing methods
Over 185 my, mammals evolved as small (size of domestic cats) and nocturnal
Development of hair and endothermy
Teeth specialized to facilitate digestion
Brain specialized for hearing and smelling
First “true mammals” present in the Jurassic Period (oldest fossil is 160 myo)
Mammals began to flourish 65 mya after the Cretaceous-Tertiary mass extinction (caused by the meteorite)

5. Characteristics of Mammals
Mammary glands
Hair
Diaphragm
Three middle-ear ossicles
Heterodont dentition
Sweat glands
Sebaceous glands (oil)
Scent glands
Four-chambered heart
Large cerebral cortex

6. Diversity of Mammals 5,400 species
Dominant terrestrial animals on every continent (even extended to the oceans)
Two lineages
Prototheria- monotremes
Theria- marsupials & plancental mammals

7. External Structure
Body covered in two-layered skin (epidermis & dermis)
Used for protection & temperature regulation
Hair- unique to mammals
Grows from a follicle in the skin
Pelage- coat of hair
2 Types:
Long guard hairs- protection
Short underhairs- insulation
Periodically molt old hairs
May grow a thicker pelage in the winter and/or change pelage color

8. External Structure Other hair functions: Sense of touch Insulation
Air spaces
Arrector pili muscle
Muscle around hair follicle that contracts & allows the hair to stand upright
Amount of air trapped in the pelage increases, which provides more insulation
Also contract in response to threat (fight-or-flight)
Allows the animal to look bigger
Camouflage- color due to melanin
Hair reduced in large mammals in hot climates (hippo) and aquatic mammals (whales)

9. External Structure
Claws- used for locomotion & offensive/defensive behavior
May modify to form nails or hooves
Sebaceous glands- secretes oil to waterproof & lubricate the hair & skin
Sudoriferous glands- secretes sweat that aids in cooling
Scent or musk glands- secrete pheromones for defense, recognition, & territory
Mammary glands- present in all mammals, but only functional in females
Secrete milk to nourish young
Secreted through nipples or teats in most mammals
Monotremes secrete milk from the skin and into depressions on the belly

10. Skull & Teeth
Heterodont- teeth are specialized for different functions
Teeth are set in sockets of the jab
2 sets of teeth throughout life
1st- deciduous or milk teeth
2nd- adult/permanent teeth
4 kinds of teeth-
Incisors- front teeth, used for gnawing or nipping
Canines- long & conical, used for catching, killing, and tearing prey
Premolars- truncated for chewing
Molars- broad surface, used for chewing
Dental formula- each mammal species has a set # of teeth

11. Dental Formula
Teeth of the upper jaw above teeth of the lower jaw in the order: incisors, canine, premolars, & molars

12. Nutrition & Digestion Digestive tract specialized for diet
Many different diets
Insectivores- anteaters
Omnivores- bears
Carnivores- lions
Herbivores- horses
Enlarged cecum in the intestines to digest cellulose (thanks to microorganisms)

13. Circulation, Gas Exchange, & Temperature Regulation
Four chambered heart
Circulatory system allows maternal and fetal blood exchanges across the placenta
Breathe with lungs
Diaphragm allow air to enter the lungs
Maintain temperature with insulating fat layers & cool with longer appendages and/or sweating

14. Winter Sleep & Hibernation
Winter sleep – burrowing under the snow and become less active (still alert)
Hibernation- hypothalamus of the brain slows the metabolic, heart, & respiratory rates
“True hibernators”- Monotremes, moles, shrews, rodents, & bats
Lose around 1/3-1/2 of body weight during hibernation
Aroused from hibernation occurs by metabolic heating (takes several hours)

15. Nerves & Senses Complex brain
May communicate over long distances through olfaction (smelling)
Vision is an important sense
Color vision not as developed as reptiles (except for primates)

16. Reproduction & Development
Internal fertilization
Most mammals are viviparous (give birth to live young)
Advantage: allows the mother to remove ties to a nest
Disadvantage: growing a fetus requires a lot of energy
Oviducts are modified into one or two uteri
Reproductive cycles: Most have definite times during the year to mate
Usually determined by the season
Estrus cycle- when females are receptive to males
Determined by hormones
Some mammals begin ovulating post copulation
Gestation period- length of time young develop within the female reproductive tract
Altricial young- helpless at birth
Precocial young- walk and run shortly after birth