Pseudosuchians (Pseudosuchia) are archosaurs that include modern crocodilians and their extinct relatives. The name “Pseudosuchia” means “false crocodiles” and that makes it a bit odd because crocodiles are pseudosuchians too.  The group name Pseudosuchia was originally given to a group of superficially crocodile-like prehistoric animals from Triassic period, but it was later used to refer the crocodilian-line archosaurs when it was realized that crocodilian descended from some of these Triassic animals.
Pseudosuchians appeared during Early Triassic and soon they took over the niches left from therapsids that went extinct in Permian–Triassic mass extinction or the Great Dying. They ruled ruled the world during most Triassic, but later on the dinosaurs were also diversifying