BIOL 2200 Chapter Notes - Chapter 34: Thumb, Platypus, Echidna
31 Mar 2017
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34. 6 mammals are amniotes that have hair and produce milk. Derived characters of mammals: mammary glands produce milk for offspring, hair, fat layer under skin retains heat, endothermic; most have high metabolic rate, respiratory and circulatory systems, larger brain, differentiated teeth (different shapes and sizes) Early evolution of mammals: mammals belong to an early group of amniotes called synapsids. Have a hole behind eye-socket: during early cretaceous (140 mya), 3 major lineages arose: monotremes (egg- laying animals), marsupials (mammals with a pouch) and eutherians (placental mammals) Monotremes: found only in australia and new guinea, 1 species of platypus, 4 species of echidna, lack nipples, instead milk is produced by glands on mother"s belly. Eutherians (placental mammals: placentas more complex than those of marsupials, longer pregnancy than marsupials, complete embryonic development within uterus, connected to the mother by placenta. Early primates were tree dwellers and had many adaptations to allow them to live in trees.
