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OriginsThe Search for Our Prehistoric Past$
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Frank H. T. Rhodes

Print publication date: 2016

Print ISBN-13: 9781501702440

Published to Cornell Scholarship Online: January 2017

DOI: 10.7591/cornell/9781501702440.001.0001

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The Mammalian Explosion

The Mammalian Explosion

Chapter:
(p.188) 13 The Mammalian Explosion
Source:
Origins
Author(s):

Frank H. T. Rhodes

Publisher:
Cornell University Press
DOI:10.7591/cornell/9781501702440.003.0013

This chapter looks specifically at the placental mammals. The distinctive feature of this extraordinary group is that they bear live young, with the embryo being nourished within the mother's womb by a placenta, which is fixed to the wall of the uterus. Marsupial mammals also have placentas, and in order to distinguish between the two groups, the “true” placental mammals (that is, the nonmarsupial mammals) are frequently described as Eutheria, as described in the previous chapter. Most placental mammals have an enlarged braincase; and the teeth are differentiated into a typical pattern of three incisors, one canine, four premolars, and three molars on each side of the upper and lower jaws. The placental mammals are organized into five major groups, and this chapter selects a few of these to illustrate some of the remarkable changes they have undergone over the course of Cenozoic time.

Keywords:   mammals, placental mammals, live young, placenta, Eutheria

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