 Aetosauria was first named in 1889 by English naturalist Richard Lydekker and zoologist Henry Alleyne Nicholson . They considered Aetosauria to be one of three suborders of the order Crocodilia , the other two being Parasuchia ( a Triassic group ) and Eusuchia ( a group including all post @-@ Triassic crocodiles ) . At the time , Cope considered Aetosauria to belong to Rhynchocephalia , an order of reptiles that includes the living tuatara . He also thought that the tightly fitting osteoderms , which were thought to be fused to the ribs , indicated that aetosaurs were transitional between rhynchocephalians and turtles . Nicholson and Lydekker placed a single family within the suborder , Aëtosauridæ . They considered aetosaurs to be similar to living crocodilians apart from their elongated metatarsals , which were compared to those of dinosaurs . In fact , Marsh considered aetosaurs to be closely related to dinosaurs because both had similar metatarsals . 
