Updated August 9, 2019
with a recently downloaded loaded photo of the skull (Fig. 3) from Maisch, Matzke and Rathgeber 2013. The DGS version sutures are distinct from those of Maisch et al.. The LRT nesting did not change.
Dyoplax arenaceus (Fraas 1867, Lucas, Wild and Hunt 1998) is a unique Late Triassic crocodylomorph, one of the three original crocodylomorphs in the 19th century along with two aetosaurs.
No bones are present.
Like Cosesaurus it is a natural cast mold. Fraas thought it had the head of a lizard, but the armor of a gavial. Lucas et al. nested it as the oldest sphenosuchian crocodylomorph. Maish et al. nested it with Erpetosuchus.
Dyoplax nests as a basal metriorhynchid, those Jurassic sea crocodiles with flippers for fore limbs and a curved fish-like tail (Fig. 2), which was probably too early to be present. Unfortunately the tail tip and limb tips are missing from the fossil (Fig. 1)
The fossil appears to have no arch of bones separating the upper and lateral temporal fenestrae, but the intervening squamosal appears to be flipped and displaced near the neck ribs. (Black arrow in fig. 1)
Fraas O 1867. Dyoplax arenaceus, ein neuer Stuttgarter Keuper-Saurier. Jh. Verein vaterländ. Naturk. Württemberg 23:108-112; Stuttgart.
Lucas SG, Wild R, Hunt AP 1998. Dyoplax O. Fraas, a Triassic sphenosuchian from Germany. Stuttgarter Beiträge zur Naturkunde, B. 263: 1–13.
Maisch MW, Matzke AT and Rathgeber T 2013. Re-evaluation of the enigmatic archosaur Dyoplax arenaceus O. Fraas, 1867 from the Schilfsandstein (Stuttgart Formation, lower Carnian, Upper Triassic) of Stuttgart, Germany. Neues Jahrbuch für Geologie und Paläontologie – Abhandlungen. 267 (3): 353–362.