Infraclass Metatheria (Marsupialia)

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The marsupials or metatherians are almost certainly a monophyletic group.  The following characters, other than 1-3, are for the most part primitive for eutherians and metatherians.

Characters

  1. cheek teeth consist of 3 premolars and 4 molars [Figures from Animal Diversity Web; 1, 2 3, 4, 5]
  2. only the third deciduous premolar is replaced
  3. neonate attached to nipple for extended period of lactation [Fig. 20-13]
  4. large palatal vacuities are typically present [Fig. 6-3 left]
  5. inflected angular process
  6. choriovitelline placenta in most [Fig. 20-10]
  7. marsupium in most
  8. epipubic bones in both sexes, possible functions are discussed in Wikipedia
  9. uteri completely separate, double lateral vaginal canals [fig. 6-5]
  10. penis bifurcate, without baculum
  11. scrotum anterior to penis 

Biogeography

    1. The Mesozoic World [Fig. 25-3]
      1. Pangea
      2. Gondwana and Laurasia
      3. a North American origin
      4. the South America, Antarctica, Australia connection [Figs. 25-3C]
      5. Cretaceous biogeography, image by Dr. Ron Blakey - http://jan.ucc.nau.edu/~rcb7

    1. Wallace's Line

      1. Map from Wikipedia by Maximilian Dörrbecker (Chumwa)

     

    1. Many marsupials, especially in Australia, occupy similar niches as placental mammals elsewhere as a result of  convergent evolution:

      1. similar features from different ancestors as a result of ecological equivalence 
      2.   convergence in placental and marsupial mammals- Dr. George Johnson's Backgrounder
      3. Another term used to describe convergence is ecomorph.  Ecomorphs are distantly related taxa with similar morphologies that occupy similar niches.   Ecomorphs typically are similar in both dietary preferences, feeding adaptations, and locomotor adaptations.

     

     
    1. Thylacosmilus an extinct South American marsupial sabertooth [Fig. 6-7B]
      1. Figure from E. S. Riggs, 1933, Preliminary Description of a new marsupial sabertooth from the Pliocene of Argentina.  Geological Series Of Field Museum Of Natural History, Volume 6, pages 61-66 .


         


Infraclass Metatheria: 

Order Didelphimorphia
Family Didelphidae  
  1. American opossums [15 genera, 63 species]
  2. Neotropical and Nearctic
  3. didelphids tend to be unspecialized.
  4. 5/4 incisors
  5. prehensile tail
  6. opposable big toe (hallux)
  7. paired sperm, also occurs in the Caenolestidae. A synapomorphy for Ameridelphia
  8. most are omnivorous. Didelphis virginiana
  9. the Caluromyinae are folivorous; Marmosa and other mouse opossums [Thylamyinae and Marmosinae] are insectivorous.
  10. Chironectes (from northern S. A.), the water opossum, has webbed feet adapted to its swimming lifestyle. It is exclusively piscivorous
  11. I Dedelplimorphi from the Italian L'Associazione TERRAMBIENTE.

 

Order Paucituberculata
Family Caenolestidae
(Nt)

  1. "shrew" or "rat" opossums [3 genera, 6 species]
  2. distributed throughout the higher forested elevations of the Andes in South America.
  3. small, shrew-like animals of insectivorous and omnivorous habits
  4. large, procumbent, medial lower incisors are used to stab their prey.

 

 
Order Microbiotheria
Family Microbiotheriidae (South America)
  1. a single living species Dromiciops australis (Fig. 6-12)
    1. small mouse-like insectivores 
    2. enlarged bullae
    3. incisors 5/4
  2. DNA hybridization data suggests they are related to Australian dasyurids
  3. eats mistletoe fruit and deposits the sticky seeds intact onto the trunks of shrubs [Amico, G. and Aizen, M.A. 2000. Mistletoe seed dispersal by a marsupial. Nature 408(6815):929-930.]
  4. Learn how the Colo-colo drinks the saliva  of sleeping people and what to do if you find one in your house from Grace Palmer at Art Progress and Neat Animal of the Day

 

Monito del Monte by Jose Luis Bartheld from Valdivia, Chile, from Wikipedia

Order Dasyuromorphia (A)
Family Dasyuridae [15 genera, 61 species]
  1. marsupial "mice", native "cats" [Fig. 6-13], and "Tasmanian Devil"
  2. 4/3 incisors
  3. tail not prehensile
  4. pouch usually absent, if present opens posteriorly
  5. ecological equivalent of didelphids
  6. insectivores, carnivores, and scavengers
  7. Sarcophilus; the Tasmanian Devil
  8. [Fig. 6-16A]
    1. 4-10 kg
    2. Sarcophilus from Tasmania Online
  9. Males of the marsupial mouse Antechinus (Fig. 20-18) and the Brush-tailed Marsupial Mouse are semelparous [pp. 398-399].  Almost all other mammal species are iteroparous.

 

Antechinus stuartii; Broad-footed Marsupial Mouse
Dr. Lloyd Glenn Ingles
; 2001 California Academy of Sciences

Family Myrmecobiidae
  1. Myrmecobius: the numbat or marsupial "anteater"
  2. myrmecophagous
    1. long extensible tongue for feeding on ants or termites.
    2. Numbat numbers in decline: Impact of foxes, cats, humans
 numbat (Myrmecobius fasciatus),
The numbat (Myrmecobius fasciatus).  Image from Wikipedia
Family Thylacinidae
  1. Tasmanian "tiger or wolf"
  2. Thylacinus cynocephalus; 1500-2000 mm long [fig 6-16B]
  3. extinct in Australia and New Guinea, almost certainly in Tasmania, by 1936
  4. Visit The Thylacine Museum  by Cameron Campbell
 Thylacine (Thylacinus cynocephalus), which became extinct in 1936.
Thylacinus cynocephalus. Image from Wikipedia
Order Notoryctemorpha (A)
Family Notoryctidae
  1. marsupial "mole"
  2. the only completely fossorial marsupial
    1. fossorial adaptations

Syndactyla (A)

Characters

  1. Syndactyly [fig. 6-15]
  2. Upper molars with hypocone

Order Peramelorpha

Characteristics

Families

  1. Family Peramelidae
    1. non-spiny bandicoots
      1. bilbies or rabbit-eared bandicoots  [Fig. 6-17]
      2. brown bandicoot
    2. Perameles nasuta -- Long-nosed Bandicoot; photograph to right by Dr. Lloyd Glenn Ingles, California Academy of Sciences. 

     

    Family Peroryctidae
    1. bandicoots that mainly occur in New Guinea 
     

 

Order Diprotodontia  

Families

 
  1. Family Vombatidae
    1. wombats  [fig 6-19]
    2. 1/1 incisors, diastema [fig 6-10D]
    3. wombat skull from ADW
    4. semi-fossorial
    5. October 22 is Wombat Day
    6. more information from Wikipedia

Vombatus ursinus, the Common wombat Cal Photos � 2005 Sharon Chester

    1. Family Phascolarctidae
      1. koala [Figs. 6-20, -21]
      2. tail vestigial
      3. Folivory
        1. feed primarily on Eucalyptus leaves
        2. hindgut fermentation specializations
      4. chorioallantoic placenta without villi
      5. Wikipedia
      6. Australian koala foundation
      7. the koala page
      8. koalas from the BigZoo

     


  1. Family Tarsipedidae
    1. honey possum: nectar feeder; pollinator
    2. long tongue with bristles at tip
    3. long prehensile tail
    Phalangeroids 
  2. Family Acrobatidae
    1. feathertail glider and feathertail possum
     

    Family Burramyidae

    1. 2 genera and 5 species of pigmy possums  [Fig. 6-22]
    2. brushy tongues
    3. includes some gliding species
    4. known only as fossils until 1966
     
    Family Pseudocheiridae
    1. ringtail possums and the greater glider
    2. formerly included in the Petauridae
    3. ringtails have a strongly prehensile tail
    4. copraphagy and bacterial fermentation in the caecum
     
    Family Petauridae
    1. lesser gliders 
      • Petaurus has a furred gliding membrane like a flying squirrel; sugar gliders are sold as pets.
      • Petaurus australis Fluffy Glider Possum;  photograph to right by Dr. Robert Thomas and Margaret Orr; California Academy of Sciences
    2. striped possums lack a gliding membrane, have an elongate fourth finger

  3. Family Phalangeridae
    1. large possums (phalangers) and cuscuses [Fig. 6-23A]
    2. highly arboreal, slow moving: loris-like
    3. prehensile tail
    4. opposable hallux and thumb.
    5. photograph of Trichosurus vulpecula, Brush-tailed Possum


    image � Dr. RobertThomas and Margaret Orr, California Academy of Sciences. 

  4.  
    Superfamily Macropodoidea

    1. Family Potoridae
      1. potoroos [Fig. 6-25A], bettongs, and the musky rat-kangaroo
      2. Tasmanian bettong from Tasmania Online
     
    1. Family Macropodidae
      1. kangaroos and wallabies [Fig. 6-25B,C]
      2. 11 genera; 56 species
      3. locomotion
        1. mainly terrestrial
        2. arboreal [Lumholtz tree-kangaroo The Tree-Kangaroo and Mammal Group Inc.]
        3. digitigrade
        4. bipedal hopping (ricochetal) [Fig. 21-28]
          1. Relationship between metabolic rate and hopping speed in red kangaroos [Fig. 21-28]
          2. Hop, Skip, and Soar: Studying animal locomotion at Harvard's Concord Field Station
      4. ecological equivalent of ungulates
        1. foregut fermentation [Fig. 6-27]
      5. kangaroo reproduction
        1. embryonic diapause: a variant of delayed implantation [p. 392]



    Tree kangaroo
    image by H. Vannoy Davis 2001 California Academy of Sciences



    2000 ZooNet/Montgomery Zoo

     

 

THE MARSUPIAL-PLACENTAL DICHOTOMY

[pp. 87-88]

Character

Marsupial state

Placental state

Diversity 6% of living mammal species 94% of living mammal species
size not as large larger range of body sizes
structural adaptations less diverse flying (wings), marine (fins)
Reproduction
[Chapter 20]
brief gestation; semiembryonic young; body mass 1% of mother [Fig. 10.11]. Need for precocious grasping forelimbs may constrain adaptability long gestation period; young more developed at birth; body mass up to 50% of mother
Placenta [Fig. 20-10] choriovitelline (usually)  chorioallantoic
Lactation period 
[Fig. 20-5]
long short
Investment of energy in motherhood [Fig. 20-16] lower, altricial young higher, reproduce more rapidly (usually), precocial young
Cerebral Cortex/ Braincase smooth and complex, slow development, smaller volume (maybe) fast development, greater volume (maybe)
Behavioural plasticity uncommon great range of behaviours
Territoriality uncommon common and important
Antipredator behaviour not well developed highly developed, particularly in herding animals; capable of sustained high speeds
Epipubic bones present absent
Baculum absent present in most
Auditory bullae derived from alisphenoid bone varies, but not alisphenoid
primitive dental formula 5/4-1/1-3/3-4/4 3/3-1/1-4/4-3/3

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