 Biochrons for aetosaur genera have been developed for dating strata in the Chinle Group of the southwestern United States. Up to 13 genera of aetosaurs are known from the Chinle Group, with most occurring in multiple localities and over short time spans. In 1996, paleontologists Spencer G. Lucas and Andrew B. Heckert recognized five biochrons based on the presence of aetosaurs throughout the Chinle Group. The number of biochrons grew to 11 in a 2007 study by Heckert and Lucas along with Adrian P. Hunt and Justin A. Spielmann. These biochrons occurred from the Otischalkian LVF to the Apachean LVF and included genera such as Longosuchus, Tecovasuchus, and Typothorax.
