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Dyoplax
''Dyoplax'' is an extinct genus of pseudosuchian archosaur. Fossils have been found from the type locality within the upper Schilfsandstein Formation in Stuttgart, 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'',〔Benton, M. J. (1986). The Late Triassic tetrapod extinction events. ''In: Padtan, K. (ed.): The Beginning of the Age of Dinosaurs'': 303-320; Cambridge. Cambridge University Press〕〔Hunt, A. P. (1993). A revision of the Metoposauridae (Amphibia: Temnospondyli) of the Late Triassic with description of a new genus from the western United States. Museum of Northern Arizona Bulletins 59:67-97; Flagstaff〕 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.
==Phylogeny==
When originally described, ''Dyoplax'' was said to have had "the head of a lizard and the armor of a gavial".〔Fraas, O. (1867). ''Dyoplax arenaceus'', ein neuer Stuttgarter Keuper-Saurier. ''Jh. Verein vaterländ. Naturk. Württemberg'' 23:108-112; Stuttgart.〕 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".〔Zittel, K. A. von (1890). Handbuch der Palaeontologie. I. Abtheilung Palaeozoologie. III Band. Vertebrata (Pisces, Amphibia, Reptilia, Aves). – XII + 900 pp., 719 figs. München & Leipzig (Oldenbourg).〕 Several other papers published in later years have also placed the genus within Pseudosuchia.〔Huene, F. von (1902). Ubersicht über die Reptilien der Trias. ''Geol. paläont. Abhandlungen, N. F.'' 6(1): 1-84; Jena〕〔McGregor, J. H. (1906). The Phytosauria, with especial reference to Mystriosuchus and Rhytidodon. ''Memoirs of the American Mususeum of Natural History'' 9:29-101; New York.〕〔Huene, F. von (1942). Lieferungen 3/4. Pseudosuchia, Saurischia, Rhynchosauridae und Schlussabschnitt. ''Die Fossilen Reptilien des Südamerikanischen Gondwanalandes. Ergebnisse der Sauriergrabungen in Südbrasilien 1928/29. C. H. Beck'sche Verlagsbuchhandlung, München'' 161-332〕〔Romer, A.S. Vertebrate Paleontology. University of Chicago Press, Chicago; 2nd edition (1945).〕 In 1956 the genus was referred to Notochampsidae, now known as Protosuchidae.〔Romer, Alfred Sherwood (1956). ''Osteology of the Reptiles''. Chicago. University of Chicago Press. pp. 1–772. ISBN 0-89464-985-X.〕 It was suggested to be a possible erpetosuchid in 1966,〔Romer, A.S. Vertebrate Paleontology. University of Chicago Press, Chicago; 3rd edition (1966) ISBN 0-7167-1822-7〕〔Carroll, R.L. (1988). ''Vertebrate Paleontology and Evolution''. WH Freeman and Company, New York ISBN 0-7167-1822-7〕 but was later classified as one of the earliest protosuchids in 1994.〔Benton, M. J. (1994). Late Triassic to Middle Jurassic extinctions among continental tetrapods: Testing thepattern. ''In: Fraser, N. C. & Sues, H-D. (eds.): In the Shadow of the Dinosaurs'': 366-397; Cambridge. Cambridge University Press.〕
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 because it lacked four out of five of the synapomorphies associated with Aetosauria.
''Dyoplax'' was first considered to be within the suborder Sphenosuchia 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. The age of the specimen within the strata would make ''Dyoplax'' 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''. However, Maisch, Matzke and Rathgeber (2013) questioned the placement of ''Dyoplax'' within Crocodylomorpha, and claimed that it shared important cranial and postcranial features with ''Erpetosuchus''; the authors tentatively re-assigned ''Dyoplax'' to Erpetosuchidae.〔
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