6.7: Placental Mammals
- Page ID
- 62163
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The terms 'marsupial' and 'placental' were established in the late 18th century when mammals were first classified. 'Marsupial' is derived from the Latin word marsupium, meaning pocket. As you know, this feature is conspicuous in kangaroos and wallabies but is not present in all marsupials. Then the need for renaming was even more evident once marsupials were found to briefly form a simple placenta. So the terms Eutheria (= placental mammals), Metatheria (= marsupials) and Prototheria (= monotremes) were proposed instead. The net benefit is that the young of placental mammals are often born relatively mature after a prolonged pregnancy, with all the attendant benefits to their early wellbeing that size can bring. The efficiency of the mammalian placenta is another factor that helps explain the group's biological success - an evolutionary flowering that the following units illustrate to full effect. Characteristics of Mammals: thermoregulation, body hair, lactation, larger brains.
http://www.oercommons.org/courses/studying-mammals-a-winning-design/view
Openstax CNX; History of our Tribe (Barbara Helm Welker)