Biochronology
Because species of aetosaurs typically have restricted fossil ranges and are abundant in the strata they are found in, they are useful in biochronology. Osteoderms are the most common remains associated with aetosaurs, so a single identifiable scute can accurately date the layer it is found in.
Aetosaur biochronology -255 — – -250 — – -245 — – -240 — – -235 — – -230 — – -225 — – -220 — – -215 — – -210 — – -205 — – -200 — – Jurassic Permian Triassic Induan Olenekian Anisian Ladinian Carnian Norian Rhaetianr
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Palæozoic
Axis scale: millions of years ago.
References: Lucas et al. (1998), Heckert et al. (2007)
One aetosaur, Typothorax coccinarum, has been used to define the Revueltian land vertebrate faunachron. A land vertebrate faunachron (LVF) is a time interval that is defined by the first appearance datum (FAD), or first occurrence, of a tetrapod index fossil and is commonly used to date Late Triassic and Early Jurassic terrestrial strata. Since the FAD of T. coccinarum is at the beginning of the Norian stage, the Revueltian LVF starts at the beginning of the Norian around 216 million years ago. The Revueltian ends with the next FAD, which happens to be that of the phytosaur Redondasaurus and the start of the Apachean LVF.
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.
Read more about this topic: Aetosaurs