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KEY CONCEPT Reptiles, birds, and mammals are amniotes. Amniote embryos develop in a fluid-filled sac. The amniotic sac contains everything an embryo needs to grow. some develop inside mother’s body some develop inside a tough, semipermeable shell.
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Amniote embryos develop in a fluid-filled sac. • The amniotic sac contains everything an embryo needs to grow. • some develop inside mother’s body • some develop inside a tough, semipermeable shell
AllantoisHolds waste materialsas the embryo grows Embryo AmnionProtects andsurrounds theembryo Yolk sac Contains the nutrient supply for the growing embryo Chorion Allows gas exchange with outside environment • The amniotic egg allowed vertebrates to reproduce on land.
Anatomy and circulation differ among amniotes. • The first animals walked in a sprawl. • Other amniotes, including dinosaurs, evolved a more upright stance.
All amniotes have two circuits of blood vessels. • pulmonary circuit moves blood from the heart to the lungs • systemic circuit moves blood from the heart to the rest of the body
THREE-CHAMBERED HEART FOUR-CHAMBERED HEART • Amniotes have a three- or four-chambered heart. • reptiles hearts have three chambers • birds and mammals hearts have four chambers
Amniotes can be ectothermic or endothermic. • Amniotes manage body heat in different ways. • Ectotherms have body temperatures determined by the surrounding environment. • Endotherms use metabolic heat to keep tissues warm. • Endotherms can live in a wider range of climates than ectotherms.