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Marsupials have the typical characteristics of mammals—e.g., mammary glands, three middle ear bones, (and ears that usually have tragi, [3] varying in hearing thresholds [4]) and true hair. [5] There are, however, striking differences as well as a number of anatomical features that separate them from eutherians .
Figure 1:In mammals, the quadrate and articular bones are small and part of the middle ear; the lower jaw consists only of dentary bone.. While living mammal species can be identified by the presence of milk-producing mammary glands in the females, other features are required when classifying fossils, because mammary glands and other soft-tissue features are not visible in fossils.
A partial middle ear formed by the departure of postdentary bones from the dentary, and happened independently in the ancestors of monotremes and therians. The second step was the transition to a definite mammalian middle ear, and evolved independently at least three times in the ancestors of today's monotremes, marsupials and placentals. [38]
Therefore, when combining the models, scientists could predict that marsupials migrated from what is now South America, through Antarctica, and then to present-day Australia between 40 and 30 million years ago. A first marsupial fossil of the extinct family Polydolopidae was found on Seymour Island on the Antarctic Peninsula in 1982. [160]
Paucituberculata / ˌ p ɔː s ɪ tj uː ˌ b ɜːr k j uː ˈ l eɪ t ə / is an order of South American marsupials.Although currently represented only by the seven living species of shrew opossums, this order was formerly much more diverse, with more than 60 extinct species named from the fossil record, particularly from the late Oligocene to early Miocene epochs.
The Macropodidae are an extant family of marsupial with the distinction of the ability to move bipedally on the hind legs, sometimes by jumping, as well as quadrupedally. They are herbivores , but some fossil genera like Ekaltadeta are hypothesised to have been carnivores . [ 1 ]
Sparassodonta (from Greek σπαράσσειν [sparassein], to tear, rend; and ὀδούς, gen. ὀδόντος [odous, odontos], tooth) is an extinct order of carnivorous metatherian mammals native to South America, related to modern marsupials.
Early mammals and possibly their eucynodontian ancestors had epipubic bones, which serve to hold the pouch in modern marsupials (in both sexes). 170-120 Ma Juramaia sinensis. Evolution of live birth , with early therians probably having pouches for keeping their undeveloped young like in modern marsupials.