Mammalia

...The oldest of this group is the Placodermi, which appeared in the Late Silurian and flourished until the Permian. It is believed that the first to branch off from this group (in the Late Ordovician) was the Chondrichthyes, but their fossils do not appear until the Middle Devonian, later than the Osteichthyes, which also branched off from the Placodermi. The Amphibia, which branched off from the Crossopterygii, a subclass of the Osteichthyes that acquired bones, and acquired limbs and lungs, appeared during the transition from the Devonian to the Carboniferous. The Reptilia, a reptile that branched off from the Amphibia and acquired an amniotic membrane, appeared in the Late Carboniferous. The Aves, a bird that branched off from the Archosauria subclass of reptiles and acquired feathers, appeared in the Early Jurassic. The Mammalia, a mammal that branched off from the Synapsida subclass of the Synapsida and acquired split hairs, mammary glands, and three middle ear ossicles, appeared in the Late Triassic. The classes Agnathida, Placoderms, Chondrichthyes, and Osteichthyes are sometimes grouped together in the superclass Pisces, with the remaining classes grouped in the superclass Tetrapoda.

*Some of the terminology that mentions "Mammalia" is listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

…この類で最古のものはシルル紀後期に現れ二畳紀まで栄えた板皮類(綱)Placodermiで，これから最初に分かれた(オルドビス紀後期)のが軟骨魚類Chondrichthyesと推定されているが，これの化石は，やはり板皮綱から分かれデボン紀前期に現れた硬骨魚類Osteichthyesよりも後のデボン紀中期にならないと姿を見せない。硬骨を獲得した硬骨魚綱の中の総鰭類(亜綱)Crossopterygiiから分かれ，四肢と肺を獲得した両生類Amphibiaはデボン紀から石炭紀への移行期，両生綱から分かれ羊膜を獲得した爬虫類Reptiliaは石炭紀後期，爬虫類の祖竜亜綱Archosauriaから分かれ羽毛を獲得した鳥類Avesはジュラ紀前期，同じく爬虫綱の単弓亜綱Synapsidaから分かれ毛と乳腺および3個の中耳小骨を獲得した哺乳類Mammaliaは三畳紀後期に現れている。無顎綱，板皮綱，軟骨魚綱，および硬骨魚綱を合わせて魚類Pisces，残りのものを四足動物Tetrapodaの2上綱とすることがある。…

※「Mammalia」について言及している用語解説の一部を掲載しています。

出典｜株式会社平凡社世界大百科事典 第２版について | 情報