BSC 116 Lecture Notes - Lecture 18: Flightless Bird, Plesiosauria, Ectotherm
4 Jun 2016
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Document Summary
Amniotes and the evolution of terrestrial vertebrates part 1. Amniotes are named for the major derived character of the clade, the amniotic egg, which contains four specialized membranes: the amnion, the chorion, the yolk sac, and the allantois. Called extraembryonic membranes because they are not part of the body of the embryo itself, these membranes develop from tissue layers that grow out from the embryo. Plus albumen: egg white : amnion: encloses a compartment of fluid that bathes the embryo and acts as a hydraulic shock absorber, chorion: gas exchange, allantois: waste storage, yolk sac: nutrient storage. A shell; hard or leathery- slows dehydration of the egg in air, an adaption that helped amniotes to occupy a wide range of terrestrial habitats than amphibians, their closest relatives. Rib cage to ventilate their lungs (rather than throat); develop less permeable skin, conserving water. Includes tuataras, lizards, snakes, turtles, crocodilians, and birds. Along with extinct groups, such as plesiosaurs and ichthyosaurs.
