Mainly Triassic group of primitive thecodontian (‘tooth-in-socket’) reptiles (see thecodontia). They resembled heavily armoured crocodiles, and appear to have been specialized herbivores or possibly omnivores. They grew up to 3 m long, and their armour plating comprised rows of bony plates.

http://www.ucmp.berkeley.edu/diapsids/pseudosuchia/aetosauria.html Introduction to the Aëtosauria.