Mammals!!!

1. Mammals!!! NB #159 Write this on your own paper

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 • Arrectorpili 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