Dyoplax
Encyclopedia
Dyoplax is an extinct genus
of sphenosuchia
n crocodylomorph
. Fossil
s 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 lagoon
al paleoenvironment
. Numerous bivalves, chondrichthyean
fish
such as Palaeobates, trematosauria
n 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
.
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 referred 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 because 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.
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of sphenosuchia
Sphenosuchia
Sphenosuchia is a suborder of basal crocodylomorphs that first appeared in the Triassic and occurred into the Late Jurassic. Most were small, gracile animals with an erect limb posture. They are now thought to be ancestral to crocodyliforms, which include all living crocodilians.-Stratigraphic...
n crocodylomorph
Crocodylomorpha
The Crocodylomorpha are an important group of archosaurs that include the crocodilians and their extinct relatives.During Mesozoic and early Tertiary times the Crocodylomorpha were far more diverse than they are now. Triassic forms were small, lightly built, active terrestrial animals. These were...
. Fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
s have been found from the type locality within the upper Schilfsandstein Formation in Stuttgart-Feuerbach
Stuttgart-Feuerbach
Feuerbach is a district of the city of Stuttgart. Its name is derived from the small river of the same name that flows from the neighbouring district of Botnang through Feuerbach...
, Germany
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
. The formation was deposited during the early Carnian
Carnian
The Carnian is the lowermost stage of the Upper Triassic series . It lasted from about 228.7 till 216.5 million years ago . The Carnian is preceded by the Ladinian and is followed by the Norian...
stage of the Late Triassic
Late Triassic
The Late Triassic is in the geologic timescale the third and final of three epochs of the Triassic period. The corresponding series is known as the Upper Triassic. In the past it was sometimes called the Keuper, after a German lithostratigraphic group that has a roughly corresponding age...
228 million years ago in a lagoon
Lagoon
A lagoon is a body of shallow sea water or brackish water separated from the sea by some form of barrier. The EU's habitat directive defines lagoons as "expanses of shallow coastal salt water, of varying salinity or water volume, wholly or partially separated from the sea by sand banks or shingle,...
al paleoenvironment
Paleoecology
Paleoecology uses data from fossils and subfossils to reconstruct the ecosystems of the past. It involves the study of fossil organisms and their associated remains, including their life cycle, living interactions, natural environment, and manner of death and burial to reconstruct the...
. Numerous bivalves, chondrichthyean
Chondrichthyes
Chondrichthyes or cartilaginous fishes are jawed fish with paired fins, paired nares, scales, two-chambered hearts, and skeletons made of cartilage rather than bone...
fish
Fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
such as Palaeobates, trematosauria
Trematosauria
Trematosauria is one of two major groups of temnospondyl amphibians that survived the Permian-Triassic extinction event, the other being the Capitosauria. The trematosaurs were a diverse and important group that included many medium-sized to large forms that were semi-aquatic to totally aquatic...
n temnospondyls
Temnospondyli
Temnospondyli is a diverse order of small to giant tetrapods—often considered primitive amphibians—that flourished worldwide during the Carboniferous, Permian, and Triassic periods. A few species continued into the Cretaceous. Fossils have been found on every continent...
such as Metoposaurus
Metoposaurus
Metoposaurus is an extinct genus of temnospondyl amphibian, known from the Late Triassic of Europe. This mostly aquatic animal possessed small, weak limbs, had sharp teeth and a large flat head. The main diet of this highly flattened creature was fish which it captured with its wide jaws lined with...
, a phytosaur
Phytosaur
Phytosaurs are an extinct group of large semi-aquatic Late Triassic archosaurs. Phytosaurs belong to the family Phytosauridae and the order Phytosauria. They were long-snouted and heavily armoured, bearing a remarkable resemblance to modern crocodiles in size, appearance, and lifestyle, an example...
, and plants such as Neocalamites and Equisetites were also present in the paleoenvironment that existed at the time. The holotype
Holotype
A holotype is a single physical example of an organism, known to have been used when the species was formally described. It is either the single such physical example or one of several such, but explicitly designated as 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
Hesperosuchus
Hesperosuchus is an extinct genus of crocodylomorph reptile that contains a single species, Hesperosuchus agilis. Remains of this sphenosuchian have been found in Late Triassic strata from Arizona and New Mexico....
and Parrishia
Parrishia
Parrishia is an extinct genus of sphenosuchian crocodylomorph that is currently considered a nomen dubium because of the lack of diagnostic features associated with it...
.
Phylogeny
When originally described, Dyoplax was said to have had "the head of a lizardLizard
Lizards are a widespread group of squamate reptiles, with nearly 3800 species, ranging across all continents except Antarctica as well as most oceanic island chains...
and the armor of a gavial
Gharial
The gharial , , also called Indian gavial or gavial, is the only surviving member of the once well-represented family Gavialidae, a long-established group of crocodilians with long, slender snouts...
". When the taxon Pseudosuchia
Pseudosuchia
Pseudosuchia is the name originally given to a group of prehistoric reptiles from the Triassic period. The name has been variously interpreted, and it is still sometimes, if infrequently, used in scientific literature today. A more commonly used name, Crurotarsi, is often substituted for...
was first proposed in 1890, Dyoplax was considered one of the three genera within the clade
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
, 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 referred to Notochampsidae, now known as Protosuchidae
Protosuchidae
Protosuchidae was a family of crocodylmorph reptiles from the Late Triassic, Jurassic, and Cretaceous time periods.-Distribution:Triassic protosuchids are known from Lesotho and Arizona. Jurassic protosuchids are known from Nova Scotia, Poland, South Africa, and Arizona...
. 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
Synapomorphy
In cladistics, a synapomorphy or synapomorphic character is a trait that is shared by two or more taxa and their most recent common ancestor, whose ancestor in turn does not possess the trait. A synapomorphy is thus an apomorphy visible in multiple taxa, where the trait in question originates in...
characteristic of the clade Aetosauria. This confirmed that Dyoplax was not within the order
Order (biology)
In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...
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 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
Paul Sereno
Paul Callistus Sereno is an American paleontologist from the University of Chicago who discovered several new dinosaur species on several continents. He has conducted excavations at sites as varied as Inner Mongolia, Argentina, Morocco, and Niger...
& 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
Squamosal
The squamosal is a bone of the head of higher vertebrates. It is the principal component of the cheek region in the skull, lying below the temporal series and otic notch and bounded anteriorly by postorbital. Posteriorly, the squamosal articulates with the posterior elements of the palatal complex,...
. On this basis, the authors concluded that there was enough evidence to place Dyoplax within Sphenosuchia, a phylogenetic
Phylogenetics
In biology, phylogenetics is the study of evolutionary relatedness among groups of organisms , which is discovered through molecular sequencing data and morphological data matrices...
position that remains to this day.
External links
- Dyoplax in the Paleobiology DatabasePaleobiology Database' is an online resource for information on the distribution and classification of fossil animals, plants, and microorganisms.-History:The Paleobiology Database was founded in 2000. It has been funded by the National Science Foundation and the Australian Research Council...