Of the 17 major groups of mammals, Australia has only five native groups: monotremes
, marsupials, bats, rodents, and seals.
In the case of the INSL3 ancestor, the duplication fluke occurred sometime before the monotremes
, marsupials and placental mammals split, but after fish and frogs became separate groups.
Management recommendations for the Marsupial & Monotreme
Taxon Advisory Group.
Far more numerous than the primitive monotremes
are the marsupials (mar soo'pee elz), which include pouched mammals like the kangaroos, koalas, and wombats.
are a unique group of animals made up of the echidna and the platypus.
produce milk for their young but lack nipples, so their milk just oozes out of mammary gland ducts and collects in grooves on patches of skin, where the nursing babies lap it up or suck it from tufts of fur.
If the tree was correct, the molar thought to belong exclusively to live-bearing mammals had evolved separately in the egg-laying monotremes
Females also have a joint urinary and genital tract, a characteristic shared with primitive mammals such as the monotremes
Those fur coats and their ability to produce milk would make them mammals, but they also lay eggs, making them officially monotremes
, a distinction they share only with the platypus.
45) For the platypus' eggs and marsupial reproduction see Kathleen Garnette Dugan, 'Marsupials and Monotremes
in Pre-Darwinian Theory', PhD thesis, University of Kansas, 1980.
They placed the platypus in a special group of mammals, the monotremes
20 species of mammals declared extinct, with almost half of Australia's marsupials and monotremes
listed as extinct, endangered or vulnerable.