amniote
Sign in to saveAmniotes are tetrapod vertebrate animals belonging to the clade Amniota, a large group that comprises the vast majority of living terrestrial and semiaquatic vertebrates. Amniotes evolved from amphibious stem tetrapod ancestors during the Carboniferous period. Amniota is defined as the smallest crown clade (the group including all descendants of the last common ancestor) containing humans, the Greek tortoise, and the Nile crocodile. Amniotes represent a crucial evolutionary step in vertebrate history, marking the transition from aquatic to fully terrestrial life.
AI overview
An amniote is a type of vertebrate animal that evolved from amphibious ancestors and includes most of today's land-dwelling and semiaquatic vertebrates, such as reptiles, birds, and mammals (including humans). Amniotes matter because they represent a major evolutionary breakthrough that allowed vertebrates to fully adapt to life on land rather than remaining dependent on water for reproduction.
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Article
11 sectionsContents
- Etymology
- Description
- Adaptation for terrestrial living
- The egg membranes
- Amniote traits
- Definition and classification
- Traditional classification
- Classification into monophyletic taxa
- Phylogenetic classification
- Cladogram
- References
Amniotes are tetrapod vertebrate animals belonging to the clade Amniota, a large group that comprises the vast majority of living terrestrial and semiaquatic vertebrates. Amniotes evolved from amphibious stem tetrapod ancestors during the Carboniferous period. Amniota is defined as the smallest crown clade (the group including all descendants of the last common ancestor) containing humans, the Greek tortoise, and the Nile crocodile. Amniotes represent a crucial evolutionary step in vertebrate history, marking the transition from aquatic to fully terrestrial life.
Amniotes are distinguished from the other living tetrapod clade — the non-amniote lissamphibians (frogs/toads, salamanders/newts and caecilians) — by: the development of three extraembryonic membranes (amnion for embryonic protection, chorion for gas exchange, and allantois for metabolic waste disposal or storage); internal fertilization; thicker and keratinized skin; costal respiration (breathing by expanding/constricting the rib cage); the presence of adrenocortical and chromaffin tissues as a discrete pair of glands near their kidneys; more complex kidneys; the presence of an astragalus for better extremity range of motion; the diminished role of skin breathing; and the complete loss of metamorphosis, gills, and lateral lines.