Dissorophus Temporal range:Kungurian,280–273 Ma PreꞒ Ꞓ O S D C P T J K Pg N
Dissorophus multicinctus skeleton
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Order:	†Temnospondyli
Family:	†Dissorophidae
Subfamily:	†Dissorophinae
Genus:	†Dissorophus Cope, 1895
Type species
†Dissorophus multicinctus Cope, 1895

Dissorophus (DI-soh-ROH-fus) (meaning "double roof" for two layers of armor) is an extinctgenus oftemnospondylamphibian that lived during the EarlyPermian Period about 273million years ago. Its fossils have been found inTexas^[1] and inOklahoma^[2] inNorth America. Its heavy armor and robust build indicateDissorophus was active on land, similar to other members of thecladeDissorophidae that are known from the LateCarboniferous to the Early Permian periods.Dissorphus is distinguished by its small body size, disproportionately large head and short trunk.

The American paleontologistEdward Drinker Cope first briefly describedDissorophus in 1895,^[3] likely deriving the genus name fromAncient Greek δισσός/dissos "double" and ὀροφή/orophe "roof" to refer to the double layer of armor formed by horizontal "spinous branches" at the top of the neural spines of the vertebrae that "touch each other, forming a carapace" with overlying rows of bonyosteoderms that form an armored "dermal layer of transverse bands which correspond to the skeletal carapace beneath," a feature expressed as well in the type species namemulticinctus, meaning "many-banded" inLatin. Cope referred to the animal as "a veritable batrachian [amphibian]armadillo."

DeMar[5] mentions Boulenger's interpretation ofDissorophus as “remarkable for an extraordinary exo- and endo-skeletalcarapace",^[4] reflected in the nameDissorphus multicinctus for its double layered armor.^[5]

Additional specimens ofDissorophus were later collected by theMuseum of Comparative Zoology atHarvard College and theUniversity of Chicago, described by the paleontologistsWilliston,Case andRomer. Williston (1914) divided the Dissorophidae into two subfamilies: Aspodosaurinae and Dissorophinae. He distinguished the Aspodosaurinae as having an openotic notch and single layered armor (one armor segment per vertebral segment), and Dissorophinae as having a closedotic notch and double layered armor (two armor segments per vertebral segment).^[4]

Below is acladogram fromSchoch (2010). Schoch developed his cladogram based on an analysis of anatomical features of dissorophids. He found thatDissorophus,Broiliellus texensis,Broiliellus brevis andBroiliellus olson all share a pointedsnout as a common feature.^[6]

Schoch and Sues describe the skull ofDissorophus multicinctus as “short and broad posteriorly”. DeMar and Williston mention that the skull has two equal sides and it is flat posterior to the orbit, but curved and has depressions from anterior to margins. In addition, the skull surface shows deep circular pits or depressions situated on posterior portions of the frontals and bound by narrow ridges between them and thus difficult to distinguish sutures.^[1][7][8]

According to DeMar, the skull depth increases posteriorly and decreases anteriorly when in lateral view. He points out another prominent feature ofDissorophus which is an enlarged otic notch. Measuring up to 3.5 cm in length, the otic notch ofDissorophus is relatively deeper than some members of the family Dissorophidae who possess shallow otic notches. The presence of an otic notch firmly assures that dissorophides are indeed unified with the amphibian family because this feature present in all amphibians and lost in later amniotes. DeMar also adds that the depth of the otic notch relates to the length of the skull. In this case, short skulls would have shallow otic notches and longer skulls would possess deeper otic notches.^[1]

Carroll (1964) makes a similar observation as DeMar inBroiliellus brevus that has a short skull and therefore a shallow otic notch, as expected. On the other hand, Bolt makes a crucial comment, that the specimens used to describe these anatomical features by both DeMar and Carroll are based on that assumption that they are in "adult configurations".^[9][10] DeMar mentions that the external nares is enlarged and measures up to 1 cm long in larger specimens.^[1]

On this note, Williston adds that the external naris are elongated along the skull margins, resulting to an oval shaped outline and oriented laterally and anteriorly.^[1][7]

The orbits ofDissorophus are relatively large, circular, and oriented dorsally than laterally. As DeMar describes, theorbits are large enough to intersect with the frontals,palatines, post orbitals,lacrimals, andjugals.^[1]

DeMar also makes points out a crucial feature that suggest whyDissorophus andBroileillus are closely related to one another than any other species. This feature at the region wheremaxillary,quadratojugal andjugal meet. In this case, he illustrates that thejugal overlaps thequadratojugal andmaxillary, thus extending to the tooth rows. This feature was also observed byCarroll (1964) onBroiliellus brevis,Conjuctio andDissorophus angustus. Thus, this feature gives another explanation to the relationship betweenDissorophus andConjunctio, keeping in mind thatDissorophus andBroiliellus are more closely related to each other because they both have a pointed snout while Conjunctio does not.^[1][10]

Another distinct feature that Dissorophus has is that the maxillary teeth extend further back ventral to thesquamosal. DeMar explains this extension of teeth further back correlates with the jugal overlap on the maxillary and quadratojugal. In addition, DeMar clarifies that the contact between vomer and pterygoid is lost resulting topalatine contributing to an enlarged interpterygoid.^[1]

Williston's anatomical analysis onDissorophus reveal that there are about thirty five teeth on thedentary.^[7] Additionally, DeMar's mentions that the entire lower jaw is covered by dermal pitting except for the region of coronoid process. He also mentions that thecoronoid process extends anteriorly and serves as an attachment point for muscles and thus the most probable diet inferred would be a carnivore likely to prey on smaller animals such as insects and smaller animals. DeMar also comments on a distinctive feature that is only present inDissorophus multicinctus and not any other dissorophids. He explains the presence of a ventral flange that interrupts the continuity of the lower jaw. Connecting to the ventral flange is a pitted surface of angular that “continues on the ventral edge and projects medially forming a small shelf.” He concludes that this arrangement of lower jaw is not found in any other dissopophid, however, the angular projection ventral to the ventral flange is also developed inBriolielus.^[1]

Williston explains that thehumerus andfemur ofDissorophus are solidly built and stouter. The humerus has "deep lateral curvatures and wide supracondicular ridges" while the femur is a lot stronger built compared to the humerus. He also mentions that the articular surface ofDissorophus femur is "flattened with sharp rims on the antero-posterior convexity". He adds that both femur and humerus are both "expanded on the inner and outer side and narrow in the middle".^[7]

The carapace is another distinctive feature present inDissorophus. Williston describes this feature as a heavy bony covering that is not necessarily broad, but long and heavy. The dorsal section is deeply pitted and the ventral section is rather smooth.^[7] In addition, Dilkes's findings show that theosteoderm is composed of an internal section and external section that are “expanded laterally”. His distinction between an internal and external section is such that the internal section is associated with a flange. The flanges are deeply notched and the edges of these notches serve as attachment points to theneural spine, this explains his hardships in trying to decipher regions of theneural spine. On the other hand, the external series are positioned anterior to the internal series. He also adds that both series are likely fused together by interosteodermal ligaments. This osteoderm feature that Dilkes makes directly correlates to Bolt's interpretations thatDissorophus has a double layered osteoderm comprising both the internal series and external series.^[7][5]

In terms of locomotion, Dilkes mentions that compared toCacops,Dissorphus likely had a more flexible vertebral column in terms oflateral flexion and axial rotation. Limitation to locomotion is solely based on anatomy of the osteoderms. As Dilkes explains, coupling betweenlateral flexion and axial rotation throughout the vertebrae, translates to limited locomotion. In the case ofCacops, Dilkes's interpretation on the 20-degree angle of inclination of thezygapophyses indicate that coupling betweenlateral flexion and axial rotation is highly limited. In addition, there is extensive overlap between internal series and external series which contributes to a limitation oflateral flexion. In the case ofDissorophus, Dilkes gives more detail that there is larger angle of inclinations ofzygapophyses indicating that there is greater coupling between the axial rotation andlateral flexion despite insertion of theflanges in theneural spine.

In conclusion, both DeMar and Dilkes clarify that the osteoderm growth covers the first sections of the anterior vertebral column and grows posteriorly with fusion of the next posterior vertebral sections. This means that reduction of flexibility starts anteriorly and proceeds posteriorly, thus it is likely that "as juveniles bothCacops andDissorophus had greater vertebral flexibility" as mentioned by Dilkes.^[11][1]

Modern amphibians are semi-aquatic. According to DeMar,Dissorophus multicinctus had made a full transition onterrestrial land, indicated by the presence of a dermal armor that made it less dependent on water and better adapted to active life on land.^[1]

His hypotheses on terrestriality include:

• “Terrestrial animals live in a medium of low density (air) thus must have stronger support in vertebral column and limbs for static stress. So it is expected that it would have features that diminish static stress such as a dorsal armor."
• "Terrestrial animals move actively on land so it would have features that assist with the activity."
• "Terrestrial animals are subject to drying so it would possess features that reduce drying.”

Some functions of the dorsal armor suggested by DeMar include;

• "Protection against predators."
• "Limit mobility of the vertebral column."
• "Reduce surface subject to drying."

DeMar's suggestions on terrestriality and functions of dermal armor directly correlates to the Geological location[6] at whichDissorphus multicinctusfossils are found.^[1] According to both Williston, Schoch and information from the Paleobiology database[7],Dissorophus fossils are found in the Clear Fork Division of the Texas Red-beds of Arroyo formation.^[6][1][7]

• Dissorophids
• Carboniferous temnospondyls of North America
• Permian temnospondyls of North America
• Fossil taxa described in 1895
• Taxa named by Edward Drinker Cope
• Prehistoric amphibian genera

• Articles with short description
• Short description is different from Wikidata
• Articles with 'species' microformats