Dyoplax

Dyoplax is an extinct genus of sphenosuchian crocodylomorph. Fossils have been found from the type locality within the upper Schilfsandstein Formation in Stuttgart-Feuerbach, Germany. The formation was deposited during the early Carnian stage of the Late Triassic 228 million years ago in a lagoonal paleoenvironment. Numerous bivalves, chondrichthyean fish such as Palaeobates, trematosaurian temnospondyls such as Metoposaurus, a phytosaur, and plants such as Neocalamites and Equisetites were also present in the paleoenvironment that existed at the time. The holotype specimen was a cast of a nearly complete skeleton that lacked only parts of the tail and limb bones. The age of the specimen within the strata shows that Dyoplax is the oldest sphenosuchian, predating other genera from the late Carnian that were once thought to be the oldest members of Sphenosuchia such as Hesperosuchus and Parrishia.

Phylogeny
When originally described, Dyoplax was said to have had "the head of a lizard and the armor of a gavial". When the taxon Pseudosuchia was first proposed in 1890, Dyoplax was considered one of the three genera within the clade, and was included within the family "Aetosauridae". Several other papers published in later years have also placed the genus within Pseudosuchia. In 1956 the genus was refered to Notochampsidae, now known as Protosuchidae. It was suggested to be a possible erpetosuchid in 1966, but was later classified as one of the earliest protosuchids in 1994.

In that same year a paper was published that identified several synamomorphies characteristic of the clade Aetosauria. This confirmed that Dyoplax was not within the order Aetosauria as had been previously speculated due to the fact that it lacked four out of five of the synapomorphies associated with Aetosauria.

Dyoplax was first considered to be within the suborder Spenosuchia in a paper published in 1998 by Spencer et al.. The authors claimed that all synapomorphies present within Crocodylomorpha, as defined in 1992 by Sereno & Wild, were present in Dyoplax. They further concluded that the genus had most of the synapomorphies common to Sphenosuchia, lacking only the forked posterior process of the squamosal. On this basis, the authors concluded that there was enough evidence to place Dyoplax within Sphenosuchia, a phylogenetic position that remains to this day.