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Mammals

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.

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Mammals

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  1. Mammals Synapsid Amniotes

  2. 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

  3. 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

  4. 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

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

  6. 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

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

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

  9. 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)

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

  11. Epidermal and dermal layers Protects against Mechanical injury Microorganisms UV rays Important in Temp regulation Sensory perception Excretion H2O regulation Skin

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

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

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

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

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

  17. Reduced pelage • Hot climates • Aquatic animals • Naked mole rats

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

  19. 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 Glands

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

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

  22. 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

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

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

  25. 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

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

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

  28. 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

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

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

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

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

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

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

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

  36. 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 Winter sleep vs. hibernation

  37. 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

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

  39. 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

  40. Behavior • Varied • Cat with arched back • Dog wagging tail • Wolf on its back

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

  42. Herd behavior • Stay calm if familiar sounds continue • Bleating • Breaking twigs • Stomach rumblings

  43. Tactile communication • Primates • Nosing • Grooming • Keeps pelage clean • Reinforces social relationships

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

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

  46. Cycles • Beneficial time to reproduce • Temperature • Rainfall • Available food • All subject to cycles

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

  48. Development • Monotremes • Oviparous • Shell glands deposit shell • Incubate eggs in ventral pouch • Lay eggs in burrow

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

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

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