Noneutherian mammals: monotremes and marsupials

Phylogenetically isolated from other mammals

I. Monotremes (Prototheria)

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

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

3. Echidna - one cool thing!
   
   
   • Convergence with other myrmecophagous species
     • Australian species eats ants and termites; New Guinea species eats earthworms
     • Tube-like rostrum covered with leathery skin
     • Edentate
     • Long tongue coated with mucous
     • "Digging" limbs (short, powerful, claws)
   
   
   
4. Platypus - two cool things!
   
   
   • Convergence with other amphibious and aquatic species
     • Dense, waterproof fur
     • No pinnae
     • Eyes and ears lie in folds of skin and are covered when underwater
       
     • Sphincter muscle closes off nares (nostrils)
       
     • Webbed feet
     
     
     
   • It's venomous! Read more here if you're interested.
     • Only males are venomous, and only during breeding season
     • Venom produced in thigh gland
     • Venom delivered through keratin ankle spur on hind leg
       
       

II. Marsupials (Metatheria)

1. General characteristics:
   • 50% have pouches (marsupia) form of pouch varies with ecology: kangaroo-opens up top; opens towards the hind legs
   • For those with no pouches, young just dangle underneath females attached to nipples
   • Epipubic bones
     • Found in both sexes; whether or not they have pouches
     • Once thought to support the pouch, but there's new evidence that they stiffen the torso and prevent lateral flexion of the spine during locomotion

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

   Phylogeny and biogeography

   New classifiation system based on incisor teeth and digits.

   • Teeth are either diprotodont ("two front teeth") or polyprotodont ("many front teeth")
   • Digits are either didactylus (separate; ancestral state) or syndactylus ("together toes")

   Examples

   • Order Diprotodontia (kangaroos) - Diprotodont dentition and syndactylus digits
   • Order Didelphimorphia (Virginia opossum) - Polyprotodont dentition and didactylus digits
   
   
   

3. Examples of convergence between marsupials and placental mammals

   Placental	Marsupial
   cat	quoll
   Artiodactyl skull	kangaroo skull
   flying squirrel	sugar glider
   mole	marsupial moles (fossorial, insectivorous, vestigial eyes, no pinnae, robust forelimbs)
   marmot skull	wombat (marmot-like teeth, minimal tail)
   wolf skull	thylacine (see especially 3:57-4:40 of video) skull

4. 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. cats)
      4. Introduction of diseases for which native species had no immunity
   4. Interesting extinct species:

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