Some examples of the diversity of the crocodile-line archosaurs or Crurotarsi. This group was very common and diverse in the Triassic, and only a bit less so in the Jurassic and Cretaceous. Many of them were highly specialized and seem to have been active, possibly even warm-blooded animals. The group has many interesting examples of convergent evolution with dinosaurs and other groups. Now only the modern crocodiles remain.
In this picture, from top to bottom:
Saltwater Crocodile, Crocodylus porosus. The largest modern species of crocodile. An opportunistic predator that can eat anything from water buffalo to sharks.
Yacarerari. Belongs to the Cretaceous group Notosuchia. It was a cat-sized animal with very unusual mammal-like teeth.
Metriorhynchus. Member of the completely aquatic group Thalattosuchia. It had a tail fin and it's limbs were modified into flippers. It might have been viviparous, since it's body plan sure doesn't look suitable for laying eggs on dry land. Thalattosuchians are strongly convergent with ichthyosaurs and dolphins.
Terrestrisuchus. A small, obviously cursorian Sphenosuchian that could have weighed around 15 kg. It might be a juvenile specimen of Saltoposuchus.
Postosuchus. A member of Rauisuchia. It might have been partly or completely bipedal, since it's front limbs are small and weak. It was a large predator that had very similar head and teeth as the tyrannosaurid dinosaurs.
Effigia. Another dinosaur-like rauisuchian. It was a fast-running, bipedal animal very similar to ornithomimosaurs (the ostrich-mimic dinosaurs). It even had a toothless beak.
Desmatosuchus. A triassic aetosaur with very impressive armour. It was a herbivore with a surprisingly pig-like head.
Rutiodon. A crocodile-like phytosaur. Despite their appearance, phytosaurs were not closely related to the modern crocodiles. They seem to be another example of convergent evolution.