This lesson explains how the amniotic egg and its supporting membranes helped vertebrates reproduce away from open water. These adaptations distinguish amniotes from amphibians and provide important support for a developing embryo.
The amniotic egg is the key reproductive adaptation shared by amniotes. Reptiles, birds, and mammals are amniotes, although most mammals develop their embryos inside the mother's body rather than laying eggs. The amniotic egg protects an embryo and provides it with resources while allowing gas exchange with the environment.
All flashcards
What is an amniotic egg?
An egg containing an embryo enclosed by an amnion and supported by extraembryonic membranes. It protects and nourishes the embryo while allowing gas exchange.
What does the amnion do?
It surrounds the embryo with fluid, cushioning it from mechanical shock and helping maintain hydration.
What are the functions of the chorion and allantois?
The chorion facilitates oxygen and carbon dioxide exchange. The allantois stores nitrogenous waste and also contributes to respiration.
How does the yolk sac nourish an embryo?
Blood vessels in the yolk sac transport nutrients from the yolk into the embryo's circulatory system.
How does mammalian development use amniote membranes?
The embryo remains enclosed in the amnion. In most mammals, a placenta derived in part from the chorion and allantois supports nutrient transport, gas exchange, and waste management.
Quiz questions
Which lineages arose from the early branching of amniotes?Answer: Synapsids, leading to mammals, and sauropsids, including reptiles and birds.
What are temporal fenestrae in amniote skulls?Answer: Openings behind the eyes associated with space for jaw muscles.
Which statement correctly describes the evolutionary origin of birds?Answer: Birds evolved from theropod dinosaurs within the saurischian lineage.
How do turtles ventilate their lungs despite having ribs incorporated into the shell?Answer: They change pressure around the lungs by moving limbs and internal organs.
What supports the wing membrane of a pterosaur?Answer: An elongated fourth finger supports the membrane, with a pteroid bone supporting the forewing.
Based on Biology 2e by Mary Ann Clark, Matthew Douglas, Jung Choi (OpenStax), licensed CC BY 4.0. Adapted into a summary, flashcards and quizzes.