Reassessment of the aetosaur 'Desmatosuchus' chamaensis with a reanalysis of the phylogeny of the Aetosauria (Archosauria: Pseudosuchia)

Study of aetosaurian archosaur material demonstrates that the dermal armour of Desmatosuchus chamaensis shares almost no characters with that of Desmatosuchus haplocerus. Instead, the ornamentation and overall morphotogy of the lateral and paramedian armour of 'D.' chomaensis most closely resembles that of typothoracisine aetosaurs such as Paratypothorax. Autapomorphies of 'D.'chamoensis, for example the extension of the dorsal eminences of the paramedian plates into elongate, recurved spikes, warrant generic distinction for this taxon. This placement is also supported by a new phylogenetic hypothesis for the Aetosauria in which 'D.' chamaensis is a sister taxon of Paratypothorax and distinct from Desmatosuchus. Therefore, a new genus, Heliocanthus is erected for 'D.' chamaensis. Past phylogenetic hypotheses of the Aetosauria have been plagued by poorly supported topologies, coding errors and poor character construction. A new hypothesis places emphasis on characters of the lateral dermal armour, a character set previously under-utilised. Detailed examination of aetosaur material suggests that the aetosaurs can be divided into three groups based on the morphology of the lateral armour. Whereas it appears that the characters relating to the ornamentation of the paramedian armour are homoplastic, those relating to the overall morphology of the lateral armour may possess a stronger phylogenetic signal.