Amniota
Amniota (pronunciation: /æmˈniː.ətə/) is a clade of tetrapod vertebrates comprising the reptiles, birds, and mammals. Amniotes lay their eggs on land or retain the fertilized egg within the mother, and are distinguished from the anamniotes (fishes and amphibians), which typically lay their eggs in water.
Etymology
The term "Amniota" derives from the Greek words "amnion" (ἀμνίον), meaning "lamb", and "otos" (ὠτός), meaning "ear". This is in reference to the amniotic sac that surrounds the embryo, which is a key characteristic of this group.
Characteristics
Amniotes are characterized by having an egg with an amnion, a membrane that surrounds the embryo and helps prevent desiccation (drying out). Other key characteristics include a sturdy skull and complex nervous system, and the ability to excrete waste as urea.
Classification
Amniotes are typically divided into two main classes: the Sauropsida (reptiles and birds) and the Synapsida (mammals). These two groups are distinguished by various features of their skulls and other bones.
Evolution
The first amniotes appeared during the Carboniferous period, around 340 million years ago. They evolved from amphibian ancestors, and their development of an amniotic egg allowed them to colonize dry land more effectively than their predecessors.
See also
External links
- Medical encyclopedia article on Amniota
- Wikipedia's article - Amniota
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