主竜類は中生代の陸と空を支配した

主竜類は三畳紀に出現し、中生代の陸上生態系の頂点に君臨した爬虫類である。「直立する足」や「眼窩の前に穴（前眼窩窓）」などで特徴づけられる。しかし、中にはそれらの特徴を二次的に失ったものもいる。

主竜類にはワニ類を含む「クルロタルシ類」と、翼竜類・恐竜類を含む「鳥頸類」がある。クルロタルシ類の中にはワニ類など、水生適応を果たすものが現れ、鳥頸類の中には大空を羽ばたき、空の生態系を支配するものまで現れた。

しかし、中生代の終わりには鳥類とワニ類を除いて全て絶滅してしまった。

The Archosaurs ruled Mesozoic’s land and sky

Archosaurs appeared during the Triassic period and was a group of prosperous reptiles reigning at the top of the Mesozoic terrestrial ecosystem. Despite the fact that some Archosaurs will lose later some of these features, they were characterized by a hole in front of the orbital (before orbital window) in their skulls and by the erected posture they adopted on their feet. The Archosaur group is composed of the Crurotarsi group, which contains the crocodilian, and the Ornithodira group composed of the Pterosauria and the Dinosauria. The Crurotarsi group was quite diversified and while crocodile adapted to the aquatic life, some members of the Ornithodira group flapped into the sky, governing empty ecosystems. At the end of the Mesozoic Era, despite their successes through this era, all Archosaurs but birds and crocodiles went extinct.