Dyoplax

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Dyoplax
Temporal range: 228  Ma
Dyoplax holotype.jpg
Original lithographic illustration of the holotype of Dyoplax arenaceus, from Fraas, 1867
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Clade: Archosauria
Clade: Pseudosuchia
Clade: Suchia
Family: Erpetosuchidae
Genus: Dyoplax
Fraas, 1867
Type species
Dyoplax arenaceus
Fraas, 1867

Dyoplax is an extinct genus of pseudosuchian archosaur, possibly an erpetosuchid. Fossils have been found from the type locality within the upper Schilfsandstein Formation in Stuttgart, Germany. The holotype specimen was a natural cast of a nearly complete skeleton that lacked only parts of the tail and limb bones. [1]

Contents

Classification

Oscar Fraas, the original describer of Dyoplax, described the specimen as having "the head of a lizard and the armor of a gavial". [2] 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". [3] Several other papers published in later years have also placed the genus within Pseudosuchia. [4] [5] [6] [7] In 1956 the genus was referred to Notochampsidae, now known as Protosuchidae. [8] It was suggested to be a possible erpetosuchid in 1966, [9] [10] but was later classified as one of the earliest protosuchids in 1994. [11]

In that same year a paper was published that identified several synapomorphies characteristic of the clade Aetosauria. [12] 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.

A paper published in 1998 by Spencer et al. considered Dyoplax to be within Sphenosuchia, a grade of basal crocodylomorphs. [13] The authors claimed that all synapomorphies present within Crocodylomorpha, as defined in 1992 by Sereno & Wild, were present in Dyoplax. [14] 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 known at the time, predating other genera from the late Carnian that were once thought to be the oldest members of Sphenosuchia such as Hesperosuchus and Parrishia . [15] However, Maisch, Matzke and Rathgeber (2013) questioned the placement of Dyoplax within Crocodylomorpha, and argued that it shared important cranial and postcranial features with Erpetosuchus ; the authors tentatively reassigned Dyoplax to Erpetosuchidae. [1]

Paleoecology

The Shilfsandstein Formation was deposited during the early Carnian stage of the Late Triassic (~ 228 million years ago) in a lagoonal paleoenvironment. Numerous bivalves, chondrichthyan fish such as Palaeobates , trematosaurian temnospondyls such as Metoposaurus , [16] [17] a phytosaur, and plants such as Neocalamites and Equisetites were also present in the paleoenvironment that existed at the time.

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<i>Procompsognathus</i> Extinct genus of dinosaurs

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<span class="mw-page-title-main">Aetosaur</span> Extinct order of heavily armoured reptiles

Aetosaurs are heavily armored reptiles belonging to the extinct order Aetosauria. They were medium- to large-sized omnivorous or herbivorous pseudosuchians, part of the branch of archosaurs more closely related to crocodilians than to birds and other dinosaurs. All known aetosaurs are restricted to the Late Triassic, and in some strata from this time they are among the most abundant fossil vertebrates. They have small heads, upturned snouts, erect limbs, and a body ornamented with four rows of plate-like osteoderms. Aetosaur fossil remains are known from Europe, North and South America, parts of Africa, and India. Since their armoured plates are often preserved and are abundant in certain localities, aetosaurs serve as important Late Triassic tetrapod index fossils. Many aetosaurs had wide geographic ranges, but their stratigraphic ranges were relatively short. Therefore, the presence of particular aetosaurs can accurately date a site in which they are found.

<i>Gracilisuchus</i> Genus of fossil reptiles

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<span class="mw-page-title-main">Pseudosuchia</span> Clade of reptiles

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<span class="mw-page-title-main">Sphenosuchia</span> Suborder of reptiles

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<i>Terrestrisuchus</i> Genus of terrestrial crocodylomorph

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<i>Tarjadia</i> Extinct genus of reptiles

Tarjadia is an extinct genus of erpetosuchid pseudosuchian, distantly related to modern crocodilians. It is known from a single species, T. ruthae, first described in 1998 from the Middle Triassic Chañares Formation in Argentina. Partial remains have been found from deposits that are Anisian-Ladinian in age. Long known mostly from osteoderms, vertebrae, and fragments of the skull, specimens described in 2017 provided much more anatomical details and showed that it was a fairly large predator. Tarjadia predates known species of aetosaurs and phytosaurs, two Late Triassic groups of crurotarsans with heavy plating, making it one of the first heavily armored archosaurs. Prior to 2017, most studies placed it outside Archosauria as a member of Doswelliidae, a family of heavily armored and crocodile-like archosauriforms. The 2017 specimens instead show that it belonged to the Erpetosuchidae.

<span class="mw-page-title-main">Suchia</span> Clade of reptiles

Suchia is a clade of archosaurs containing the majority of pseudosuchians. It was defined as the least inclusive clade containing Aetosaurus ferratus, Rauisuchus tiradentes, Prestosuchus chiniquensis, and Crocodylus niloticus by Nesbitt (2011). Generally the only pseudosuchian group which is omitted from Suchia is the family Ornithosuchidae, although at least one analysis classifies ornithosuchids as close relatives of erpetosuchids and aetosaurs. Phytosaurs are also excluded from Suchia, although it is not certain whether they qualify as pseudosuchians in the first place.

<span class="mw-page-title-main">Erpetosuchidae</span> Extinct family of reptiles

Erpetosuchidae is an extinct family of pseudosuchian archosaurs. Erpetosuchidae was named by D. M. S. Watson in 1917 to include Erpetosuchus. It includes the type species Erpetosuchus granti from the Late Triassic of Scotland, Erpetosuchus sp. from the Late Triassic of eastern United States and Parringtonia gracilis from the middle Middle Triassic of Tanzania; the group might also include Dyoplax arenaceus from the Late Triassic of Germany, Archeopelta arborensis and Pagosvenator candelariensis from Brazil and Tarjadia ruthae from Argentina.

<i>Incertovenator</i> Extinct genus of probable archosaur

Incertovenator is an extinct genus of archosauriform reptile, likely an archosaur, of uncertain affinities. Its unstable position is a result of possessing a number features found in both the bird-line avemetatarsalian archosaurs and the crocodylian-line pseudosuchians. The type and only known species is I. longicollum, which is known from single specimen discovered in the Late Triassic Ischigualasto Formation of Argentina. Incertovenator is known almost entirely by its vertebral column. This indicates that it had a relatively long neck, leading to its uncertain classification due to the convergent evolution of elongated neck vertebrae in both avemetatarsalian and pseudosuchian archosaurs.

References

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  2. Fraas, Oscar (1867). "Dyoplax arenaceus, ein neuer Stuttgarter Keuper-Saurier". Jahreshefte des Vereins für vaterländische Naturkunde in Württemberg. 23. Stuttgart: 108–112.
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