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

Mammal Taxonomy Kingdom: Animalia Phylum: Chordata Subphylum: Craniata Infraphylum: Vertebrata Class: Mammalia

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

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)

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

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

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

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)

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

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

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

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)

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

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)

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)

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