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Mammals

Mammals. Class Mammalia. Small number of species ~4500 But probably more successful than most animal groups (except insects) at exploiting all available environments. Class Mammalia. Very diverse group not constrained by particular lifestyle (like flight in birds)

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Mammals

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  1. Mammals

  2. Class Mammalia • Small number of species ~4500 • But probably more successful than most animal groups (except insects) at exploiting all available environments

  3. Class Mammalia • Very diverse group not constrained by particular lifestyle (like flight in birds) • Diversity makes it difficult for layperson to identify various mammals as being closely related

  4. Class Mammalia • Descended from therapsid reptiles with mammal-like characteristics • Important structural changes from reptiles to mammals

  5. Class Mammalia • Limbs from lateral to ventral • Higher center of gravity - less stability • Required greater development of cerebellum - muscular coordination center in brain

  6. Class Mammalia • Separation of air and food passageways in head • Can breathe with mouth full of food • Allows prolonged chewing & some early digestion

  7. Subclass Theria • Most mammals belong to Subclass Theria • Descended from some common ancestor ~150 million years ago

  8. Subclass Theria • Infraclass Metatheria - marsupials - pouched mammals • Infraclass Eutheria - placental mammals

  9. Subclass Prototheria • Monotremes • Small group of egg-laying mammals • So different from other groups of mammals • Entirely different origin?

  10. All mammals • Characteristics unique and diagnostic for mammals • Hair - greatly reduced in aquatic mammals • Mammary glands - milk secreting glands for nourishing young

  11. Integument & Derivatives • Skin generally thicker than in other vertebrates • Dermis thicker than epidermis • Epidermis very thin where covered with hair, thicker on palms, soles

  12. Integument & Derivatives • Hair derived from epidermis • Probably evolved from reptilian scales • Scales still present in some (tail of rat, beaver)

  13. Integument & Derivatives • Grows from follicle • Epidermal structure sunk deep into dermal layer and beyond • Grows by addition of new cells at base of follicle

  14. Integument & Derivatives • Cells pushed upward die from lack of nourishment • Dead cells mostly keratin - same material in nails, claws, feathers

  15. Integument & Derivatives • Hair consists of 3 layers • Medulla - core • Cortex - contains pigment • Cuticle - composed of imbricated scales • Different types of hair result from differential development of the 3 layers

  16. Integument & Derivatives • Each follicle has muscle attached to it - erector muscle • Contraction causes hair to stand up straight • Increase insulation thickness, serve as warning

  17. Fur or Pelage • Most mammals have two kinds of hair • Thick, soft underhair - provides insulation • Coarse, long guard hair - protects and provides coloration

  18. Fur or Pelage • Hair stops growing when it reaches certain length • Remains in follicle until new growth starts, then falls out

  19. Fur or Pelage • Mammals lose hair in periodic molts • Most have 2 annual molts - entire pelage shed (humans shed and replace continually) • Spring - thin summer • Fall - heavy winter

  20. Fur or Pelage • Pigmentation and molts allow mammals to be different colors in different seasons • Brown in summer • White in winter - leukemism

  21. Fur or Pelage • Lack of pigment results in albinism - recessive gene - blocks pigment formation (don’t confuse with leukemism) • Excess of black pigment is melanism

  22. Derivatives of Hair • Vibrissae - sensory hairs on snouts, other parts of head • Incorrectly called whiskers

  23. Derivatives of Hair • Quills - defensive structures in porcupines, hedgehogs, echidnas • Break off after barbed tip embeds in flesh of other animal • Work in deeper with time

  24. Glands • Mammals also have variety of epidermal glands • Greatest variety among vertebrates • 4 basic types

  25. Glands • Sweat glands - simple, tubular, highly coiled • Cover most of body • Not found in other vertebrates • Open directly to skin surface • Two types

  26. Glands • Sweat glands - eccrine glands • Secrete watery sweat for temperature regulation • Hairless regions in most mammals (especially foot pads)

  27. Glands • Some mammals don’t have eccrine glands - rodents, rabbits, whales • Some have them all over body - humans, horses, dogs • Racial differences in abundance in humans

  28. Glands • Sweat glands - apocrine glands • Found in all mammals • Longer, more winding than eccrine glands • Open into follicle at surface • Secretion not involved with heat regulation

  29. Glands • Apocrine gland activity correlated with some aspects of sexual cycles • Human females have twice as many as males

  30. Glands • Scent glands - location and function vary • Communication, warning, defense, attraction • E.g., skunk • Humans have many, but taught to dislike their scent

  31. Glands • Sebaceous glands - associated with hair follicle • Secrete fat (sebum) to keep hair and skin soft • Polite fat - does not turn rancid • Generally all over body - most numerous on human scalp, face

  32. Glands • Mammary glands - modification of apocrine, sebaceous glands? • Present in both genders, functional only in female • Secrete milk to nourish young

  33. Glands • Contain varying quantities of fat (3-5%), protein, carbohydrate, salts • Higher fat content (30-40%) in marine and arctic mammals, where development is rapid

  34. Horns & Antlers • 3 kinds of horns or horn-like structures found in mammals • 1) true horns • 2) antlers • 3) rhino horns

  35. Horns & Antlers • True horns • Found in ruminants like cows, goats, antelope • Hollow sheaths of keratinized epidermis surrounding core of bone arising from skull

  36. Horns & Antlers • Not normally shed • Not branched (but may be greatly curved, twisted) • Found in both sexes

  37. Horns & Antlers • Antlers • Deer family (Cervidae) • Generally males only (except caribou - female’s smaller) • Entirely bone when mature

  38. Horns & Antlers • Annual growth • Develop beneath cover of highly vascularized soft skin - velvet • Growth complete, blood vessels constrict, velvet dies and is rubbed off

  39. Horns & Antlers • Antlers dropped after breeding season • New buds appear within few months • New pair larger, more elaborate • Strain on mineral metabolism - moose, elk must accumulate 50+ lbs of calcium salts from vegetable diet

  40. Horns & Antlers • Rhinoceros horn • Hairlike horny fibers arise from dermal papillae • Cemented together to form single horn • Dagger handles and medicinal uses

  41. Teeth • Teeth are a less obvious characteristic of mammals • Reveal more about lifestyle than any other characteristic • Not in monotremes, some whales, anteaters

  42. Teeth • Diphyodont teeth - two sets of teeth • Set of deciduous “milk teeth” replaced by set of permanent teeth • Reptiles have polyphyodont teeth - many sets - all are homodont - uniform, unspecialized

  43. Teeth • Mammals have heterodont teeth - specialized for various functions

  44. Teeth

  45. Teeth • Incisors - snip, bite - simple crowns, slightly sharp edges

  46. Teeth • Canines - piercing - pointed, long conical crowns

  47. Teeth • Premolars - shear, slice - flat compressed crowns with 1 or 2 cusps

  48. Teeth • Molars - crushing, grinding - broad with variable cusp arrangement • Always belong to the permanent set

  49. Teeth • Different diets necessitate differing development of different teeth • Carnivores - large canines, some small and/or modified molars and premolars

  50. Teeth • Rodents and herbivores - large incisors, reduced canines, large molars • Incisors grow continually, must be worn away to keep pace with growth

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