 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 fenestrae , or holes , that opened on the side of the skull rather than the top , lateral osteoderms articulating with the paramedians , and osteoderms covering the limbs . Aetosaurus was still found to be the most basal member , but the phylogeny of more derived aetosaurs differed in that Typothorax and Paratypothorax were split into two different clades with their sister taxa being Desmatosuchus and Longosuchus , respectively . More importantly , a new aetosaur called Coahomasuchus was included in the analysis . Coahomasuchus was found to be a basal aetosaur closely related to Stagonolepis , and also appeared early in the fossil record of aetosaurs . Previously , basal members were only known from later times , occurring after more advanced aetosaurs . 
