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Biology Notes 4-2-08 - -Therians placental live birth(all...

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Biology Notes April 2, 2008 How did vertebrates colonize land? Small mammals coexisted with dinosaurs for millions of years. Mammals increased in size and number after the extinction of dinosaurs. Characteristics of Mammals: -Sweat, scent, oil and mammary glands -hair -four-chambered heart -muscular diaphragm -endothermic with high activity -two sets of teeth, set into sockets -secondary bony palate -3 middle-ear bones, fleshy external ears -mother feeds milk to young Mammal eggs are fertilized internally; embryos undergo a development period in the uterus of the female (gestation). All mammals feed their offspring milk, produced in the mammary glands of females (lactation). Living mammals (5,000 species in two major groups: - Prototherians: lack placenta, lay eggs.
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Unformatted text preview: -Therians: placental, live birth (all other mammals) Prototherians such as duck-billed platypus and echidnas lack a placenta, lay eggs and have sprawling legs. Therian clade has two subdivisions:-Marsupials: carry and feed young in a ventral pouch. Young are born after short gestation, and crawl into pouch for further development (long lactation).-Eutherians- placental mammals. Young are more developed at birth. (longer gestation, shorter lactation). Diversity among the eutherians:-Rodents are most abundant.-Bats evolved flight. -Aquatic whales and dolphins evolved from even-toed hoofed mammals (hippos, deer).-Primates radiated from a small, arboreal, insectivorous mammal. Ectothermy vs. endothermy: INSERT IMAGE OF ECTO VS ENDO...
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