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(from greek ἀμνίον amnion, “membrane surrounding the fetus”)
(earlier “bowl in which the blood of sacrificed animals was caught”)
from ἀμνός amnos, “lamb”)
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(“amniotes” are a ‘clade’ of tetrapod vertebrates comprising the ‘reptiles’, ‘birds’, and ‘mammals’ that lay their ‘eggs’ on land or retain the ‘fertilized egg’ within the mother)
(they are distinguished from the ‘anamniotes’ (‘fishes’ and ‘amphibians’), which typically lay their eggs in water)
(older sources, particularly prior to the 20th century, may refer to amniotes as “higher vertebrates” and anamniotes as “lower vertebrates”, based on the discredited idea of the ‘Great Chain of Being’)
(‘amniotes’ are ‘tetrapods’ (“descendants of four-limbed and backboned animals”) that are characterized by having an egg equipped with an ‘amnion’, an adaptation to lay eggs on land rather than in water as the ‘anamniotes’ (including ‘frogs’) typically do)
(‘amniotes’ include ‘synapsids’ (‘mammals’ along with their extinct kin) and ‘sauropsids’ (‘reptiles’ and ‘birds’), as well as their ancestors, back to ‘amphibians’)
(‘amniote embryos’, whether laid as eggs or carried by the female, are protected and aided by several extensive membranes)
(in ‘eutherian mammals’ (such as ‘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, referred to as “basal amniotes”, resembled ‘small lizards’ and evolved from the ‘amphibian reptiliomorphs’ about 312 million years ago, in the ‘Carboniferous’ geologic period)
(their eggs could survive out of the water, allowing ‘amniotes’ to branch out into drier environments)
(the eggs could also “breathe” and cope with wastes, allowing the eggs and the amniotes themselves to evolve into larger forms)
(the ‘amniotic egg’ represents a critical divergence within the ‘vertebrates’, one enabled to reproduce on ‘dry land’—free of the need to return to water for reproduction as required of the ‘amphibians’)
(from this point the ‘amniotes’ spread around the globe, eventually to become the dominant land vertebrates)
(very early in the evolutionary history of ‘amniotes’, ‘basal amniotes’ diverged into 2 main lines, the ‘synapsids’ and the ‘sauropsids’, both of which persist into the ‘modern era’)
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(the oldest known fossil ‘synapsid’ is protoclepsydrops from about 312 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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*🌈✨ *TABLE OF CONTENTS* ✨🌷*
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🔥🔥🔥🔥🔥🔥*we won the war* 🔥🔥🔥🔥🔥🔥