Marsupials

Marsupialia - marsupials

 

Sarcopterygii; Tetrapoda; Amniota; Synapsida;
Theria; Metatheria; Marsupialia
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Show Southern oppossum skull lateral view Image
Southern oppossum skull lateral view
Show Southern oppossum skull lateral view Image
Southern oppossum skull lateral view
Show Southern opossum skull showing palate an dentary process Image
Southern opossum skull showing palate an dentary process
Show Southern opossum mandible showing in-turned dentary process Image
Southern opossum mandible showing in-turned dentary process

The marsupials are the sister taxon to the subclass Eutheria (placental mammals), together forming the clade Theria. Therians are then the sister clade to the monotremes, forming the group mammalia - all living mammals. The cladogram below shows these relationships:

Mammalian phylogeny

Diversity and Lower Taxonomy:

The marsupials are 335 extant species across seven orders of mammals from Australasia and the Americas, which originated in the Early Cretaceous of North America.

Three of these orders are now restricted to the Americas - including opossums, shrew opossums and the charismatic Monito del Monte - while the other four are restricted to Australasia - including kangaroos, possums, marsupial moles, bandicoots, and carnivorous marsupials such as the tasmanian devil. Below is a list of these orders with their representative groups:

o Didelphimorphia - American opossums

o Paucituberculata - shrew opossums

o Microbiotheria - Monito del Monte

o Notoryctemorphia - marsupial moles

o Dasyuromorphia - Australian carnivorous marsupials

o Peramelemorphia - bandicoots and bilbies

o Diprotodontia - kangaroos, wallabies, possums, wombats, and koala



Features:

  • After a brief gestation in the womb with no placenta (except bandicoots), the females of certain species give birth to extremely immature young, who then develop to maturity through suckling in the mother's pouch.
  • In-turned process in the dentary.
  • Three premolars and four molars. (NB. This is the ancestral marsupial dentition, however, many species have actually modified this character to have a varying number of molars and premolars)
  • Three premolars and four molars. (NB. This is the ancestral marsupial dentition, however, many species have actually modified this character to have a varying number of molars and premolars)
  • Epipubic bones - two thin rod-like bones that extend anteriorly from the pubic bones of the pelvic girdle. These bones, although often called marsupial bones, are also seen in monotremes, and are probably a ancestral mammalian character, which was lost in the Eutheria.

 

Labelled images of an opposum skull:


Labelled image of an opoessum skullshowing in-turned process on dentary

 

 

 

 

 

 

 

 

 

 

 

Labelled upper jaw dentition of a Southern opossum





























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