Amniotes
Amniotes
Amniotes (/ˈæmni.oʊts/; from Greek ἀμνίον amnion, "membrane surrounding the fetus", earlier "bowl in which the blood of sacrificed animals was caught") are a group of tetrapods (four-limbed animals with backbones or spinal columns) that have a terrestrially adapted egg. They include synapsids (mammals along with their extinct relatives) and sauropsids (reptiles and birds), as well as their fossil ancestors.
Etymology
The term "amniote" is derived from the Greek words "amnion" (ἀμνίον), which refers to the membrane surrounding the fetus, and "otes" (οτες), which denotes belonging to a group. The term was first used in the late 19th century to classify tetrapods that have a terrestrially adapted egg.
Characteristics
Amniotes are characterized by having an egg equipped with an amnion, a membrane that protects the embryo. Other key characteristics include a relatively waterproof skin, which enables them to avoid desiccation, and internal fertilization.
Classification
Amniotes are typically classified into three main groups: Mammals, Reptiles, and Birds. These groups are distinguished by their skin structure, reproductive methods, and metabolic rate.
Evolution
The first amniotes appeared during the Carboniferous period, about 340 million years ago. They evolved from amphibian ancestors, adapting to life on land and giving rise to the mammals, reptiles, and birds of today.
See also
References
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