Neoaetosauroides, have smooth carapaces and lack spikes altogether. More recent studies (see below) have favored a third group, Typothoracinae, which like Desmatosuchinae has long spikes, but differs in having more sharply angled joints between osteoderms. Moreover, the genus Aetosauroides is now often classified outside Stagonolepididae as a non-stagonolepidid aetosaur, making the names Aetosauria and Stagonolepididae no longer synonymous. List of genera Phylogeny Aetosaur phylogeny was first investigated in 1994 by paleontologist J. Michael Parrish. Aetosauroides, Aetosaurus, Desmatosuchus, Longosuchus, Neoaetosauroides, Stagonolepis, and Typothorax were included in the phylogenetic analysis. Aetosaurs were found to form a clade with rauisuchians, which Parrish termed Rauisuchiformes. Rauisuchiformes also included the superorder Crocodylomorpha, to which living crocodilians belong. Parrish found Aetosauria to be a monophyletic group and thus a true clade consisting of a common aetosaur ancestor and all of its descendants. To phylogenetically define Aetosauria, Parrish identified five synapomorphies, or shared characteristics. The first synapomorphy concerned the jaw, with the premaxilla at its tip being edentulous (toothless), upturned, and wide to form a "shovel". Moreover, the dentary bone in the lower jaw is also toothless, upturned, and broad. The reduced size and simple conical shape of the teeth was considered another synapomorphy. Two more synapomorphies of aetosaurs are shared with crocodylomorphs, but were not considered to be an indication of a close phylogenetic relationship; the body is covered in dorsal and ventral armor to form a complete carapace, and the paramedian osteoderms are much wider than they are long, with distinctive pitting. A final synapomorphy was found in the structure of the limb bones. In all aetosaurs, the limbs are very robust, with large muscle attachments such as the deltopectoral crest of the humerus, the fourth trochanter of the femur, the intracondylar ridge of the tibia, and the iliofibularis trochanter of the fibula. In Parrish's phylogenetic analysis, Aetosaurus was found to be the most basal member of the clade, the earliest to diverge after the most recent common ancestor. After Aetosaurus, there is a polytomy of three smaller clades in which it is unknown which clade diverged first from the group. Within this polytomy there was Neoaetosauroides, a clade containing Aetosauroides and Stagonolepis, and another polytomy that included Longosuchus, Desmatosuchus, and a clade containing Paratypothorax and Typothorax. A later study by paleontologists Andrew B. Heckert and Spencer G. Lucas in 1999 expanded the number of synapomorphies that diagnose Aetosauria to 18. New synapomorphies included temporal