Amniotes (from Greek ἀμνίον
amnion, "membrane surrounding the fetus", earlier "bowl in which the blood of sacrificed animals was caught", from ἀμνός
amnos, "lamb") 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.
