Noneutherian mammals: monotremes and marsupials

Phylogenetically isolated from other mammals

monotremes-others diverged ~190 mya
marsupials-placentals diverged ~100 mya

Unique reproductive patterns

monotremes egg laying
marsupials extremely altricial young, simple placenta

I. Monotremata

Common names platypus and echidna
Families Tachiglossidae, Ornithorhynchidae
# species 5
Distribution Australia, Tasmania, New Guinea (echidna)

  1. General characteristics of the order

    1. Morphologically unique
    2. Have many reptilian characteristics
    3. Birdlike skull with elongated rostrum
    4. No teeth - Chew food with the tongue and bony plate at roof of mouth (echidna) or roughened gums (platypus)
    5. Pectoral girdle splayed as in reptiles
    6. Pelvic girdle mammal-like
    7. Epipubic bones that come up from the pelvis along the ventral surface

  1. Reproduction

    1. Lay eggs
    2. Incubate them like birds
    3. Have mammary glands and make milk
    4. No nipples
    5. Milk is secreted onto the abdominal fur (platypus) or into a temporary pouch and licked off the skin (echidna)
    6. Long periods of maternal care
    7. 1 offspring/year

  1. Echidna

    1. Morphology

      1. Round, fat body
      2. Short, thick spines covering body
      3. Tube-like rostrum covered with leathery skin
      4. Long tongue coated with mucous
      5. "Digging" limbs (short, powerful, claws)
      6. Small eyes
      7. Females have a temporary pouch for carrying eggs and babies; structure may be supported by epipubic bones

    1. Ecology and behavior

      1. Solitary
      2. Crepuscular
      3. Live in burrows
      4. Poor eyesight but great sense of smell
      5. Avoid predators by

        1) Digging down
        2) Passively by rolling into a ball and exposing spines

      6. Australian sp. eats ants and termites; New Guinea sp. eats earthworms
      7. Become torpid in cold temperature/low food availability

    1. Reproduction

      1. Lay (usually) 1 egg that hatches in 9 days
      2. After hatching it lives in its mother's pouch for 12 weeks
      3. Spines at 8 weeks
      4. At 12 weeks eyes open and baby leaves pouch for burrow
      5. Weaned at 20 weeks

  1. Platypus

    1. General characteristics

      1. Small (0.5-2 kg (<5 lbs))
      2. Adapted to aquatic life

        1) Dense fur
        2) No pinnae
        3) Eyes and ears lie in folds of skin and are covered when underwater
        4) Sphincter muscle closes off nares
        5) Webbed feet

      1. Claws for digging (web extends past claw)
      2. Ankle spurs contain venom
        Also present on male echidnas, but unknown whether they are venomous
      3. Duck-like rostrum covered with moist leathery skin; contains electroreceptors on its front edge
        another view of a platypus bill

    1. Ecology and behavior

      1. Aquatic (streams, ponds)
      2. Crepuscular
      3. Bottom feeder
      4. Eats aquatic crustaceans, insect larvae, earthworms
      5. Forages using electroreception
      6. Shows torpor
      7. Male and female burrows close together or shared

    1. Reproduction

      1. Lays 1 or 2 eggs in a burrow nest
      2. Incubates 12 days then hatches
      3. Hair at 7 weeks, eyes open at 9 weeks, suckled for 16 weeks

II. Marsupials

  1. Origins
  2. General characteristics:

    1. 50% have pouches (marsupia) form of pouch varies with ecology: kangaroo-opens up top; bandicoot (diggers)- opens on bottom
    2. Epipubic bones (both sexes; whether or not they have pouches)
    3. Uterus and vagina are biphid
    4. Penis is also biphid
    5. Teeth

      1. Different numbers of incisors on top and bottom
      2. P 3/3, M 4/4
    6. Brains are relatively small and not very convoluted

  1. Reproduction

    1. Highly altricial young
    2. Short gestation (8-43 days)
    3. Young born extremely small relative to adult size

    Dasyurus (quoll) infant 1/4,250 of adult size
    kangaroo infant 1/33,400 of adult size

    1. Organs not completely developed

      1. Heart: incomplete separation of the ventricles
      2. Lungs: no alveoli
      3. Naked
      4. Blind

    2. Well-developed front limbs for grasping fur
    3. Move to pouch or (if pouchless) grab ahold of teats
    4. Teat swells in its mouth to make a semi-permanent attachment
    5. Stays in pouch 1 week - 1 year
    6. Leaves pouch at weight roughly equivalent to birthweight of a similarly-sized placental
    7. Milk changes composition during lactation

      1. Early: high protein, low fat (for structural development)
      2. Later: low protein, high fat (for rapid increase in mass)

  1. What used to be the "order Marsupialia" is now 7 separate orders


    New classifiation system based on incisor teeth and digits.

    1. Order Didelphimorphia

      # of Genera 15
      # of Species 63
      Distribution South America

      1. Ancestral type for all marsupials
      2. 50 teeth (5/4, 1/1, 3/3, 4/4=50)
      3. Opposable, clawless hallux (for climbing?)
      4. Long prehensile tail
      5. Arboreal

    1. Order Dasyuromorphia

      # of Genera 15
      # of Species 61
      Distribution Australia

      1. Shrew- to dog-sized
      2. Marsupium absent or poorly developed
      3. Long, furry tail that is never prehensile
      4. Terrestrial
      5. Very diverse
        Small species are shrew-like
        (tiger quoll)
        Thylacinus (Tasmanian wolf, thylacine)

    1. Order Diprotodontia, Family Petauridae

      # of Genera 3
      # of Species 15
      Distribution Australia

      1. Some species convergent with flying squirrels
      2. Furred membranes between limbs
      3. Arboreal
      4. Nocturnal
      5. Eat fruit, leaves, nuts

    1. Order Diprotodontia, Family Macropodidae

      # of Genera 11
      # of Species 50
      Distribution Australia
      Common names kangaroos, wallabies

      1. Range widely in size (0.5 kg to 90 kg)
      2. Ecological equivalents of antelopes and deer
      3. Limbs are highly specialized for cursorial locomotion

        1) Elongated rear limbs
        2) Syndactyly
        3) 4th digit most important; 5th large also

      4. Bipedal
      5. Move by saltation
      6. Tails very large, used for propulsion and support
      7. Large marsupium, opens anteriorly
      8. Teeth

        1) Have a diastema
        2) Molars replaced from the rear (up to 9 of them)

    1. Order Peramelemorphia (bandicoots)

  1. Examples of convergence

    Eutherian Marsupial
    cat quoll
    flying squirrel sugar glider
    mole marsupial moles (fossorial, insectivorous, vestigial eyes,
    no pinnae, robust forelimbs)
    (marmot-like teeth, minimal tail)

  1. Diversity

    1. Now is much lower than it once was...
    2. Massive extinctions in Australia that may be the result of colonization by aboriginal humans.
    3. Later, more extinctions when Europeans reached Australia

      1. Competition with domestic livestock
      2. Clearing of habitat for agriculture
      3. Introduction of domestic species (eg. rabbit)

    1. Interesting extinct species:

      Thylacoleo lion-sized, carnassial pair, retractile claws
      artist's rendering
      fossil skeleton
      Diprotodon rhino-sized; largest marsupial ever known
      artist's rendering
      fossil skeleton
      Thylacosmilus sabre-tooth cat-like marsupial
      artist's rendering
      fossil skull