noun
Metatheria
A mammalian infraclass that includes marsupials and their extinct relatives. Used in biological taxonomy.
後獣下綱にはカンガルーやコアラなどが含まれる。
Metatheria includes kangaroos, koalas, and others.
有袋類 refers specifically to marsupials, while 後獣下綱 is a broader taxonomic group that includes marsupials and related extinct lineages.
From 後 (meta-, after) + 獣 (beast) + 下綱 (infraclass). A modern taxonomic coinage.