biol_119__lecture_7__9-16-09

biol_119__lecture_7__9-16-09 - Lecture 7, 9-16-09 Chapter...

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Lecture 7, 9-16-09 Chapter 34, continued before moving on to 40
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The gill flap, or operculum, was an important adaptation for fish because it helps with _____. A. orientation in currents A. maintaining a supply of oxygen A. sensing chemicals in water B. adjusting buoyancy C. underwater sex
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Concept 34.6: Amniotes are tetrapods that have a terrestrially adapted egg Amniotes are a group of tetrapods whose living members are the reptiles , including birds, and the mammals The evolution of amniotes from an amphibian ancestor involved many adaptations for terrestrial living including the amniotic egg , the major derived character of the clade waterproof skin increasing use of the rib cage to ventilate the lungs.
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A. Derived Characters of Amniotes Amniotes are named for the major derived character of the clade, the amniotic egg which contains specialized membranes that protect the embryo The amniotic eggs enabled terrestrial vertebrates to complete their life cycles entirely on land. In contrast to the shell-less eggs of amphibians , the amniotic eggs of most amniotes have a shell that retains water and can be laid in a dry place. The calcareous shells of bird eggs are inflexible, while the leathery eggs of many reptiles are flexible. Most mammals have dispensed with the shell . The embryo implants in the wall of the uterus and obtains its nutrition from the mother.
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The four extraembryonic membranes have various functions Figure 34.25 Shell Albumen Yolk (nutrients) Amniotic cavity with amniotic fluid Embryo Yolk sac. The yolk sac contains the yolk, a stockpile of nutrients. Blood vessels in the yolk sac membrane transport nutrients from the yolk into the embryo. Other nutrients are stored in the albumen (“egg white”). Allantois. The allantois is a disposal sac for certain metabolic wastes pro- duced by the embryo. The membrane of the allantois also functions with the chorion as a respiratory organ. Amnion. The amnion protects the embryo in a fluid-filled cavity that cushions against mechanical shock. Chorion. The chorion and the membrane of the allantois exchange gases between the embryo and the air. Oxygen and carbon dioxide diffuse freely across the shell. Extraembryonic membranes
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B. Early Amniotes: An evolutionary radiation of amniotes gave rise to two main groups, the reptiles and the synapsids . Figure 34.24 illustrates this phylogeny.
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C. Reptiles The reptile clade includes The tuatara, lizards, snakes, turtles, crocodilians, birds, and the extinct dinosaurs Reptiles Have scales made of keratin that create a waterproof barrier Lay shelled eggs on land (Figure 34.26) Most reptiles are ectothermic , absorbing external heat as the main source of body heat
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1. The Origin and Evolutionary Radiation of Reptiles The oldest reptilian fossils date to about 300 million years ago The first major group of reptiles to emerge were the parareptiles , which were mostly large, stocky herbivores
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This note was uploaded on 05/04/2011 for the course BIO 119 taught by Professor O'donnellandspear during the Spring '07 term at SUNY Geneseo.

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biol_119__lecture_7__9-16-09 - Lecture 7, 9-16-09 Chapter...

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