rdfs:comment
| - The amniotes are a group of tetrapod vertebrates that have a terrestrially adapted egg. They include mammals, birds and reptiles, as well as their fossil ancestors. Amniote embryos, whether laid as eggs or carried by the female, are protected and aided by several extensive membranes. In humans, these membranes include the amniotic sac that surrounds the fetus. These embryonic membranes, and the lack of a larval stage, distinguish amniotes from tetrapod amphibians.
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abstract
| - The amniotes are a group of tetrapod vertebrates that have a terrestrially adapted egg. They include mammals, birds and reptiles, as well as their fossil ancestors. Amniote embryos, whether laid as eggs or carried by the female, are protected and aided by several extensive membranes. In humans, these membranes include the amniotic sac that surrounds the fetus. These embryonic membranes, and the lack of a larval stage, distinguish amniotes from tetrapod amphibians. The first amniotes, which resembled small lizards, probably evolved 340 million years ago (Casineria). Their eggs could survive out of the water, allowing amniotes to branch out into drier environments. The eggs could also "breathe" and cope with waste, allowing the eggs and the amniotes themselves to evolve into larger forms. The amniotes spread across the globe and became the dominant land vertebrates. Very early in their history the amniotes split into two main lines. The oldest known fossil synapsid is Protoclepsydrops from about 320 million years ago, while the oldest known sauropsid is probably Paleothyris, in the order Captorhinida, from the Middle Pennsylvanian epoch (ca. 306-312 million years ago).
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