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The Mammals

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					  The
Mammals
Fred Searcy
  Zoology
                    Mammals
•   Kitti’s Hognosed Bat of Thailand 1.5 g
•   Blue Whale 130 metric tons
•   Ubiquitous
•   4600 species
    – Compared to
       • 9000 birds
       • 24,600 fish
       • 800,000 insects
Evolution
             Evolution
•   Synapsid ancestor
•   Excellent fossilization and preservation
•   Herbivorous and carnivorous pelycosaurs
•   Lead to carnivorous therapsids
•   Lead to cynodonts (faster metabolic rate)
     – Musculature of jaw muscles for stronger bite
     – Facilitated capture of prey and feeding
     – Turbinate bones in nasal cavity retain body
       heat by warming air prior to entry
     – Secondary bony palate to breather while
       eating (and nursing young to feed and
       breathe)
     – More upright posture
     – Muscular diaphragm for breathing
                      Characteristics
•   Hair
•   Integument with sweat, scent, sebaceous and mammary glands
•   Skull with 2 occipital condyles; secondary palate; turbinate bones; middle
    ear with incus, malleus, stapes; 7 cervical vertebrate; pelvic bones fused
•   Diphyodont dentition (2 sets of teeth); lower jaw a single, large bone
•   Moveable eyelids; fleshy external ears
•   4 chambered heart; persistent left aorta, non-nucleated erythrocytes
•   Lungs with alveoli; larynx, secondary palate to separate food passage from
    respiratory passage; muscular diaphragm
•   Metanephric kidneys with ureters into bladder
•   Highly developed brain with well developed cerebral cortex; 12 pairs cranial
    nerves
•   Endothermic and homeothermic
•   Devolution of cloaca (found only in monotremes and marsupials)
•   Separate sexes with specific organs for fertilization; male determines sex
•   Embryo in utero with placenta (except monotremes); fetal membranes:
    amnion, chorion, allantois
•   Young nourished by milk from mammary glands
    Integument & Its Derivatives
• 1st line of
  defense against
   – Infections
   – Toxins
   – Retards water
     loss
   – Cools body
   – Weatherproofin
     g chemicals
     (keratin,
     cellulose)
• Thicker where no
  hair
• Epidermis,
  dermis
                      Epidermis
• Mostly stratified
  squamous
  epithelia
• Large amounts
  of keratin
• Sloughed off as
  new formed
• Non-keratinized
  cells may
  contain melanin
                          Dermis
• 0.6 to 3mm in
  thickness
• Irregular
  connections with
  epidermis via
  papillae (papillary
  layer).
  Underneath lies
  the:
    – Dermal layer
      composed
      mostly of dense
      connective
      tissue (reticular
      layer)
                            Hair
•   Originates in
    epidermis
•   Two forms:
     – Pelage (underhair
       – soft, dense,
       insulation)
     – Guard hair
       (coarse, wear and
       tear, coloration)
•   Composed of dead
    keratinized
    epidermal cells
•   From an epidermal
    follicle
•   Three layers:
     – Medulla
     – Cortex – may
       contain pigments
     – Cuticle –
       keratinized scales
                Hair Continued
• Eventually stops growing
• Replaced with new hair
• Periodic molts
  –   Humans molt year round
  –   Foxes once a year
  –   Some may molt up to 3 times
  –   White coats in winter an example of leukemism (not
      albinism)
• Types:
  – Sensory hairs on snout (vibrissae – cat’s whiskers)
  – Quills of porcupine are hair
                      Horns & Antlers
•   True horns
     – arise from a core of bone from
       the skull
     – Enveloped in sheath of
       epidermis
     – Not shed
     – Cattle and sheep
•   Antlers
     – Shed after each breeding
       season
     – Outgrowths from skull
     – Temporarily covered in
       epidermis (velvet stage)
     – Deer, antelope, caribou
       (except for caribou, only males
       produce antlers
•   Rhino “horn” is actually fused
    hair
                    Glands
• Methods of classification
  – Mode of secretion
  – Method of discharge
  – Unicellular or multicellular
  – Structural geometry
         Mode of Secretion
• Exocrine – secrete their product to an
  internal or external surface
• Endocrine – secrete their product into
  blood stream and lymph system
• Mixed – combination of both
        Method of Discharge
• Merocrine – release product through their
  membrane and cell remains intact
• Apocrine – material released also includes
  a portion of the cell’s cytoplasm
• Holocrine – results in the destruction of the
  cell when product is released
      Composition and Structural
             Geometry
• Single cells
• Multicelluar
  – Ductless
  – Ducted
     •   Tubular
     •   Alveolar (acinar)
     •   Tubulalveolar
     •   Saccular
     •   Other variations
              Categories
•   Sweat glands
•   Scent glands
•   Sebaceous Glands
•   Mammary Glands
               Sweat Glands
•   Tubular, coiled
•   Located all over body
•   Specific to mammals
•   Produce fluid (mostly water) to cool the
    body (evaporation)
                  Scent Glands
• Various functions         Animal            Location
                            Deer              Around eyes, just
  –   Communication                           above hooves, in
  –   Marking territories                     between hooves
  –   Warning               Woodchuck         Behind eyes and
                                              on cheeks
  –   Defense
                            Muskrats, beavers, Penis
                            man y canines
                            Wolves & Foxes    Base of tail

                            Skunks, minks,    Anus
                            weasels
                            Humans            Under nose,
                                              armpits, groin
         Sebaceous Glands
• Sebum (fatty material)
  – Keeps skin and hair pliable and glossy
  – Associated with hair follicles
  – Holocrine type
  – Usually doesn’t sour or turn rancid
           Mammary Glands
•   Origin in epidermis of embryo
•   Two milk lines form along abdomen
•   Mammaries develop along milk lines
•   10 mammary glands in mammals
    (including humans)
                   Food and Feeding
•   Variety of strategies
     – Herbivorous
     – Carnivorous
     – Omnivorous
•   Variations of these
    strategies
     – Coprophagy
       (rabbits)
     – Insectivorous
     – Herbivorous
          • browsers,
          • Grazers
          • Gnawers
•   Diet tied to physical
    structure and
    metabolism of
    animal
                           Teeth
• Heterodont Dentition –
  differentiated according to
  function
   – Incisors – cutting & biting
   – Canines - piercing
   – Premolars – shearing,
     crushing, grinding
   – Molars – shearing, crushing,
     grinding
• Diphyodont Dentition (two
  sets)
   – Baby or deciduous
   – permanent
                    Dental Formulas
•   Provides numbers of specific teeth
    for upper and lower half of the jaw

    Humans    2-1-2-3         Squirrel    1-0-2-3
              2-1-2-3                     1-0-1-3
    Dog       3-1-4-2         Horse       3-0-3-3
              3-1-4-3                     3-0-3-3
    Cat       3-1-3-1         Pig         3-1-4-3
              3-1-2-1                     3-1-4-3
    Raccoon   3-1-4-2         Cow &       0-0-3-3
              3-1-4-2         Sheep       3-1-3-3
    Opossum 5-1-3-4           Deer        0-0-3-3
            4-1-3-4                       3-1-3-3
    Rabbit    2-0-3-3         Rat         1-0-3-3
              1-0-2-3                     1-0-2-3
Body Weight & Food Consumption
• Smaller the animal, faster the metabolic rate, the more
  the food required
                              Migration




•   Not all migrate
•   Few seasonal migrations
•   Most migrations center around home ranges
     – Based on food abundance
•   Longest are marine mammals
     – Gray whale 18,000 km (11,2500 miles) from Alaska to Baja California and back
          Flight & Echo Location
• Bat – only flying
  mammal
   – Nocturnal and
     crepuscular
     (active at twilight)
   – Echolocation
       • Pulses emited
         5-10 millisecs
       • Modulated at
         beginning with
         high frequency
         of 100,000 hz
         then down to
         30,000 hz
         (ultrasonic
         range)
             Reproduction
• Majority have estrous cycles
  – Monestrous vs polyestrous
  – Old World monkeys and humans have
    menstrual cycles
                       Estrous Cycles
Monestrous             Diestrous   Polyestrous   Nonseasonal

Some dogs              Raccoon     Mice          Humans

Skunks                 Dogs        Horses        Some Rats

Bears                  Some Rats   Sheep         Cattle

Seals                              Hamsters

Lynx                               Gerbils

Coyote                             Guinea Pig

Otter                              O’possum

Duck-billed Platypus               Cats

                                   Ferret

                                   Mink

                                   Rabbit
                     Estrous Cycles
Species        Average           # days in cycle
               lengths in days
Mouse, rat     0.5               4
Hamster        1                 4
Guinea pig     0.5               16                Source: University of Wyoming
                                                   at
Sheep          2                 17                http://www.uwyo.edu/wjm/repro/
Goat           3                 20                tab4-4.htm
Cattle         0.5               21
Pig            2                 21
Horse          5                 21
Elephant       4                 22
Humans         7                 28
Red Kangaroo   3                 35
Lion           9                 55
Dog            7                 60
      Reproductive Patterns
• Oviparous Mammals (Prototherians)
• Viviparous Mammals with pouches
  (Metatherians)
• Viviparous Mammals with Placenta
  (Eutherians)
 Prototherians – The Monotremes
• Gr monos = single, trema = hole)
• Egg layers
  – Duck-billed platypus
  – Echidnas
• After hatching, young feed on milk of
  mammary glands
• No nipples
          Therians – the Marsupials
•   Pouched animals who give live
    birth
•   Young crawl into pouch
     –   235 days in case of kangaroos
•   Not true placentals
     –   Have an ephemeral
         choriovitelline placenta
•   While nursing, mother often
    becomes pregnant again
     –   Undergo embryonic diapause
         where embryos don’t develop
         until first brood leave pouch
•   Not all have embryonic diapause
    – not all have pouches
•   O’possum is only North American
    marsupial – does have pouch
     –   Birth occurs 13 days after
         fertilization
     –   Young in pouch for 2-3 months
     –   Remain on mother’s body for
         additional 1-3 months
     Eutherians – The Placental
             Mammals
• Marsupials have prolonged lactation;
  placentals have prolonged gestation
• Embryo remains in uterus and nourished
  until live birth in the placenta
  – From either choriovitelline placenta or a
    chorioallantoic placenta
                               Gestation
Animal      Gestation Period

Mice        21 days

Rabbits &   30-36 days
Hares
Cats &      60 days
Dogs
Cattle      280 days

Elephants   22 months – the
            longest of mammals
Baleen      12 months
whales
Bats        4-5 months
                 Growth
• Some mammals are precocial
• Human growth is slower than any other
  mammal
• # of progeny tied to mortality rate – the
  higher the number of progeny, the higher
  the mortality rate
Subclass      Infraclass       Order           Example                 Characteristics
Prototheria   Ornithodelphia   Monotremata     Duck-billed platypus,   Egg layers, no
                                               echidnas                nipples
Theria        Metatheria       Marsupialia     O’possums, kangaroos,   Typically with an
                                               koalas, Tasmanian       abdominal
                                               wolves, wombats,        pouch, short
                                               bandicoots, numbats     uterine stay,
                                                                       long lactation
                                                                       period
Eutheria      Insectivora                      Shrews, hedgehogs,      Principle food is
                                               moles                   insects
                               Macroscelidea   Elephant Shrews         Snout-like nose
                               Dermoptera      Flying lemurs           Not lemurs,
                                                                       cannot fly - only
                                                                       glide
                               Scandentia      Tree shrews             Squirrel-like,
                                                                       tropical rain
                                                                       forests of
                                                                       southern and
                                                                       southeast Asia
                               Chiroptera      Bats                    Only true flying
                                                                       mammal
Subclass   Infraclass   Order      Example                      Characteristics


Eutheria                Primates   Prosimians, monkeys, apes,   Mostly arboreal,
                                   humans                       forelimbs often
                                                                adapted for
                                                                grasping
                                   Lemurs, aye-aye, orises,     Mostly on
                                   bush babies                  Madagascar.
                                                                Long, non-
                                                                prehensile tail,
                                                                second toe with a
                                                                claw. Wet, naked
                                                                region around
                                                                commas-shaped
                                                                nostrils
                                                                (rhinarium)

                                   Tarsiers, marmosets, New &
                                   Old World Monkeys,
                                   gibbons, gorilla,
                                   chimpanzees, orangutan,
                                   humans
Sublcass   Infraclass   Order                  Example                     Characteristics
Eutheria                                       Crepuscular and nocturnal   Prehensile tails
                                               tarsiers, new World
                                               Monkeys

                                               Marmosets & Tamarins


                                               Capuchin-like Monkeys

                                               Old World Monkeys,          No Prehensile
                                               mandrills, baboons,         tails
                                               macaques, langurs



                                               Gibbons, siamang
                                               Gorilla, Chimpanzees,
                                               Orangutans, Humans


                        Xenarthra (Edentata)   Anteaters, armadillos,
                                               sloths


                        Pholidota              Pangolins
Subclass   Infraclass   Order            Example                 Characteristics
                        Lagomorpha       Rabbits, Hares, pikas


                        Rodentia         Squirrels, rats,
                                         woodchucks
                        Carnivora        Wolves, dogs, cats,
                                         bears, weasels, sea
                                         lions, seals

                        Tubulidentata    Aardvark
                        Proboscidea      Elephants
                        Hydrocoidea      Hydraxes, coneys

                        Sirenia          Sea cows, manatees

                        Perissodactyla   Odd-toed hoofed
                                         mammals: horses,
                                         zebras, tapirs,
                                         rhinoceroses
Subclass   Infraclass   Order          Example                       Characteristics
                        Artiodactyla   Even-toed hoofed
                                       mammals: swine, camels,
                                       deer, hippopotamuses,
                                       antelopes, cattle, sheep,
                                       goats


                        Cetacea        Whales, dolphins, porpoises

				
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