300861 Lecture 1: Vertebrate biodiversity 1

• School: UWS
• Department: University of Western Sydney
• Course: 300861
• Professor: anonymous

Document Summary

Amniota, a group of limbed vertebrates that includes all living reptiles (class reptilia), birds (class. Aves), mammals (class mammalia), and their extinct relatives and ancestors. The amniotes are the evolutionary branch (clade) of the tetrapods (superclass tetrapoda) in which the embryo develops within a set of protective extra- embryonic membranes the amnion, chorion, and allantois. The amnion, chorion, and allantois of amniotes likely evolved from the embryonic tissue layer encasing a large yolk mass. In living reptiles, a sheet of cells grows outward from the embryo. This growth, in combination with the growth and torsion of the embryo itself, causes the external layers of this tissue sheet to fold over the embryo from tail to head. When these folds meet above the embryo, they fuse. The tissue sheet, which becomes a tough, fluid-filled sac called the amniotic membrane, is made up of an outer chorion layer and an inner amnion layer.