Mammals Synapsid Amniotes

Diapsids and Synapsids Diapsids are the line of reptiles and birds Synapsids are the mammal line –Showed up 320 mya –Lasted through Carboniferous and Permian periods –Ectotherms, some with large sails –No hair –Egg laying –Herbivores or predators

Emergence of Therapsids Mid-Permian period –Hindlimbs Directly under body Moved parallel to body –Trunk Ribs changed Thoracic and abdominal segments Breathe like mammals –Predatory Teeth at front for tearing Elongate jaws –Herbivores Diastema – space between front & back teeth

Mass extinction 240 mya –Siberian volcanic events –Diapsids had arisen –All but a few cynodonts were wiped out Became smaller Nocturnal – limited color vision in many mammals Mammal-like: hair and endothermy selected Specialized teeth

Another mass extinction 65 mya –Dinosaurs and many ancient birds gone –Mammals can occupy dino-niches –All modern orders by end of Tertiary period

Class Mammalia Hair Mammary glands Specialized teeth 3 middle ear ossicles (bones) Diaphragm Heterodont dentition Sweat, sebaceous, & scent glands 4 chambered heart Large cerebral cortex

Diversity of mammals 5,400 species Bumblebee bat 3-4 cm to Blue whale 30 m

Subclass Prototheria Includes Infraclass Ornithodelphia, “bird birthplace”, the monotremes –Cloaca –Oviparous (egg laying) –Controversial category

Subclass Theria Infraclass Metatheria –Marsupials –Viviparous w/short gestation time –Protective pouches –250 species in Australia and the Americas

Subclass Theria Infraclass Eutheria –Placental mammals –Born at advanced stage of development –Exchanges across placenta –Over 4,000 species, 17 orders (see table 22.1, and others throughout chapter)

Evolutionary pressures Terrestrial on all continents but Antarctica Live in all oceans Many adaptations over following slides

Skin Epidermal and dermal layers Protects against –Mechanical injury –Microorganisms –UV rays Important in –Temp regulation –Sensory perception –Excretion –H 2 O regulation

Hair Unique to mammals Keratinized product of epidermis Sits in hair follicle Pelage – hair covering –Long protective hairs –Dense, short underlayer

Hair and molting Hair = dead skin cells, must be molted –Some occurs gradually –Some have winter/summer coats Thickness Color (arctic fox)

Hair and touch Displacement of hair stimulates nerves Especially legs, arms, mouth, eyes Guard hairs – vibrissae

Hair defense Air spaces provide insulation Arrector pili, smooth muscle around hair –Makes hair stand up –When threatened –Animal looks larger & tougher

Hair color How much melanin? Dark on top Light on bottom Aposematic colors – skunk

Reduced pelage Hot climates Aquatic animals Naked mole rats

Claws Present in all amniotes Keratin over ends of digits Can be nails or hooves

Glands Sebaceous (oil) glands – lubricate and waterproof Sudoriferous (sweat) glands –Evaporative cooling –Salt, urea, water (stank) Scent or musk glands –Defense –Species/mate recognition –Territorial behavior

Mammary glands Functional in females Present/nonfunctional in males Secrete milk (water, carbs, fat, protein, minerals, antibodies) Monotremes excrete milk into “belly bowls”

Skull Reptiles – jaw articulates at 2 small bones Mammals –Bones have moved to middle ear –Jaw articulates at lower jaw bone

Sophisticated palate Hard palate at roof of mouth developed 2x –In archosaurs –In therapsids In mammals, 2ndary palate further separates mouth & nasal passages Breathe while chewing Stop to swallow

Teeth Reptiles – homodont or all the same Mammals –heterodont with different functions –Set in sockets –2 sets –Four kinds Incisors Canines Premolars molars

Specialized dentition Reduced dentition – armadillos & anteaters Omnivorous lives Grinding herbivores Gnawing rodents –Diastema –Eat close to ground Tearing carnivores

Vertebral column Five regions –2 cervical vertebrae – atlas and axis Giraffe and whale both have 7 neck vertebrae Tree sloth has 6 or 9 cervical vertebrae –Thoracic region Ribs Freedom of motion –Lumbar region - support

Legs & hips Appendages under body Move along anteroposterior plane Bones of pelvic girdle fused –Advantage for locomotion –Disadvantage for birthing

Muscles Skeleton supports weight Muscles concentrated in upper appendages Running animals have less muscle in lower legs

Feeding Digestive tract similar to other vertebrates Specialized for varied feeding –Order Carnivora – carnivores or omnivores –Insectivores – eat arthropods and soft inverts –Herbivores – eat plants & inverts on plants

Digestion Rodents have a fermentation pouch or cecum –between small & large intestine –Aids digestion of cellulose Ruminants – sheep, cattle, and deer –4 chambered stomach –1 st 3 are fermentation chambers –Microorganisms make cellulose digesting enzymes –Cud

Circulation Bird & mammal hearts – convergent evolution Placental Exchange –Maternal and fetal blood never mix –Nutrients, gases, and wastes exchange –Fetal lungs inflated at birth

Gas Exchange High metabolic rates need efficient gas exchange Long snouts warm & moisten air Lungs like sponges

Gas Exchange Inspire w/negative pressure –Contract diaphragm –Expand chest Expire 2 ways –Elastic recoil –Contraction of thoracic & abdominal muscles

Thermoregulation Shivering thermogenesis little movement Lots of heat Non-shivering thermogenesis Cellular metabolism Metabolism of brown fat

Making heat Insulated w/pelage No pelage –Lower surface temperature –Walruses –Appendages w/fur Too much heat –dissipate Too cold –Tuck in appendages –Conserve heat

Other systems Cooler veins are warmed by nearby arteries Evaporative cooling Big ears dissipate heat

Winter sleep vs. hibernation Winter sleep –Retreat to burrows –Slow down, but easily roused –Bears and raccoons Hibernation –Monotremes, rodents, bats –Body temp, respiration, heart rate, metabolism all drop –May lose 1/3 – 1/2 of body weight

Nervous system Integrated systems move to brain –Sense of touch – hair follicles –Olfaction – smell food, peers, predators –Auditory senses 3 middle ear ossicles High sensitivity to pitch –Vision Overall weak color vision Squirrel, primates, & some others see color

Excretion Mammals excrete urea –Less toxic than ammonia –Requires some water Urine thicker than blood –2x in beavers –22x in Australian hopping mice

Water loss Depends on activity, physiological state, temperature Lost in urine, feces, sweat, nursing Kangaroo rat does not drink –Dry feces –Low protein diet –Metabolism makes water

Behavior Varied –Cat with arched back –Dog wagging tail –Wolf on its back

Smell and Behavior Pheromones Recognize parents and young Breed Urinate on self Skunks

Herd behavior Stay calm if familiar sounds continue –Bleating –Breaking twigs –Stomach rumblings

Tactile communication Primates –Nosing –Grooming Keeps pelage clean Reinforces social relationships

Territoriality Mammals mark territory –Your cat isn’t nice –This is not cute  –Sea lions

Reproduction Viviparity –Requires energy –Not tied to a nest –Uterus modified to nourish fetus –Care for young

Cycles Beneficial time to reproduce –Temperature –Rainfall –Available food All subject to cycles

Cycles Estrus cycle –Behaviorally and physiologically keen to mate –Release of mature ova Monestrus, diestrus, polyestrus Delays –Delayed fertilization – bats –Embryonic diapause

Development Monotremes –Oviparous –Shell glands deposit shell –Incubate eggs in ventral pouch –Lay eggs in burrow

Pre-placental mammals Marsupials –Uterine milk –Vascular yolk sac – early placenta –8 – 40 day gestation –Another 60 – 270 days in pouch

Placental mammals Eutherian mammals –Placenta - embryonic & uterine tissue –Gestation 20 days to 19 months –Altricial - helpless newborn –Precocial – walk and run quicklywalk and run quickly