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The synapsid lineage became distinct from the sauropsid lineage in the late Carboniferous period, between 320 and 315 million years ago. [2] The only living synapsids are mammals, [3] while the sauropsids gave rise to the dinosaurs, and today's reptiles and birds along with all the extinct amniotes more closely related to them than to mammals. [2]
Synapsida [a] is a diverse group of tetrapod vertebrates that includes all mammals and their extinct relatives. It is one of the two major clades of the group Amniota, the other being the more diverse group Sauropsida (which includes all extant reptiles and birds).
Class Reptilia (reptiles, paraphyletic) Class Aves (birds) Class Mammalia (mammals) In addition to these, there are two classes of extinct armoured fishes, Placodermi and Acanthodii, both paraphyletic. Other ways of classifying the vertebrates have been devised, particularly with emphasis on the phylogeny of early amphibians and reptiles.
A mammal (from Latin mamma ' breast ') [1] is a vertebrate animal of the class Mammalia (/ m ə ˈ m eɪ l i. ə /).Mammals are characterised by the presence of milk-producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair, and three middle ear bones.
Reclassifying reptiles has been among the key aims of phylogenetic nomenclature. [8] The term Sauropsida had from the mid 20th century been used to denote a branch-based clade containing all amniote species which are not on the synapsid side of the split between reptiles and mammals. This group encompasses all now-living reptiles as well as ...
Compared with the metanephros of birds and mammals, the metanephros of reptiles is simpler in structure. [21] Unlike mammals, the kidneys of reptiles do not have a clear distinction between cortex and medulla. [43] The kidneys lack the loop of Henle, have fewer nephrons (from about 3,000 to 30,000), and cannot produce hypertonic urine.
Some extinct reptiles, such as proterosuchids and euparkeriids, also possessed these features yet originated prior to the split between the crocodilian and bird lineages. The older morphological definition of Archosauria nowadays roughly corresponds to Archosauriformes , a group named to encompass crown-group archosaurs and their close relatives.
While reptiles and amphibians can be quite similar externally, the French zoologist Pierre André Latreille recognized the large physiological differences at the beginning of the 19th century and split the herptiles into two classes, giving the four familiar classes of tetrapods: amphibians, reptiles, birds and mammals. [30]