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12 de jun. de 2023 · The amniotic egg with its complex fetal membranes was a key innovation in vertebrate evolution that enabled the great diversification of reptiles, birds and mammals. It is debated whether these ...
17 de abr. de 2019 · The amnion is a membrane derived from fetal tissue which surrounds and protects the fetus. The amnion can be found within the egg, as in lizards and birds, or the amnion can simply enclose the fetus within the uterus. Amniotes include most of the vertebrates, excluding fish and amphibians. Fish and amphibians are anamniotes, meaning “without ...
Figure 1. The key features of an amniotic egg are shown. The amniotic egg is the key characteristic of amniotes. In amniotes that lay eggs, the shell of the egg provides protection for the developing embryo while being permeable enough to allow for the exchange of carbon dioxide and oxygen. The albumin, or egg white, provides the embryo with ...
The amniotic egg of reptiles and birds is surrounded by a tough outer shell that protects the egg from predators, pathogens , damage, and drying. Oxygen passes through tiny pores in the shell, so the embryo doesn't suffocate. Inside the shell are four sacs. The first sac inside the shell is the chorion, which carries oxygen from the shell to ...
Indeed, Amniota owes its name to what may be its most distinctive attribute, a large "amniotic" egg. While most of us are most familiar with the hard-shelled eggs found in birds, Stewart (1997) showed that the first amniotic eggs probably had a flexible outer membrane, and that a mineralized (but still flexible) outer membrane is a synapomorphy of reptiles.
17 de jun. de 2020 · The appearance of the amniotic egg marks a key event in the evolutionary history of vertebrates. Its major adaptive advantage is the amnion — an enclosing membrane that prevents the embryo from ...
The amniotic egg is the key characteristic of amniotes. In amniotes that lay eggs, the shell of the egg provides protection for the developing embryo while being permeable enough to allow for the exchange of carbon dioxide and oxygen.
