主龙类（Archosauria）又名初龙类、祖龙类、古龙类，在希腊文意为「具优势的蜥蜴」，是双孔亚纲爬行动物的一个主要演化支，包含恐龙、翼龙目，现仅存鳄鱼与鸟类。

关于主龙类何时开始出现，有许多争论。有一派将二叠纪的俄罗斯主龙（Archosaurus rossicus）与原龙（Protorosaurus speneri）视为真正的主龙类，这让主龙类首次出现于晚二叠纪。而另外一派，将俄罗斯主龙与原龙分类于主龙形类（并非主龙类但关系最近），使得主龙类在早三叠纪奥伦尼克阶从主龙形类演化而来。

Archosaurs are a group of diapsid amniotes whose living representatives consist of birds and crocodilians. This group also includes all extinct dinosaurs, extinct crocodilian relatives, and pterosaurs. Archosauria, the archosaur clade, is a crown group that includes the most recent common ancestor of living birds and crocodilians. It includes two main clades: Pseudosuchia, which includes crocodilians and their extinct relatives, and Ornithosuchia, which includes birds and their extinct relatives (such as non-avian dinosaurs and pterosaurs).