Dissorophus (DI-soh-ROH-fus) (meaning "double roof" for two layers of armor) is an extinct genus of temnospondyl amphibian that lived during the Early Permian Period about 273 million years ago. Its fossils have been found in Texas and in Oklahoma in North America. Its heavy armor and robust build indicate Dissorophus was active on land, similar to other members of the clade Dissorophidae that are known from the Late Carboniferous to the Early Permian periods. Dissorphus is distinguished by its small body size, disproportionately large head and short trunk.
The American paleontologist Edward Drinker Cope first briefly described Dissorophus in 1895, likely deriving the genus name from Ancient 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 bony osteoderms 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 name multicinctus, meaning "many-banded" in Latin. Cope referred to the animal as "a veritable batrachian [amphibian] armadillo."
DeMar mentions Boulenger's interpretation of Dissorophus as “remarkable for an extraordinary exo- and endo-skeletal carapace", reflected in the name Dissorphus multicinctus for its double layered armor.
History
Additional specimens of Dissorophus were later collected by the Museum of Comparative Zoology at Harvard College and the University of Chicago, described by the paleontologists Williston, Case and Romer. Williston (1914) divided the Dissorophidae into two subfamilies: Aspodosaurinae and Dissorophinae. He distinguished the Aspodosaurinae as having an open otic notch and single layered armor (one armor segment per vertebral segment), and Dissorophinae as having a closed otic notch and double layered armor (two armor segments per vertebral segment).
Classification
Below is a cladogram from . Schoch developed his cladogram based on an analysis of anatomical features of dissorophids. He found that Dissorophus, Broiliellus texensis, Broiliellus brevis and Broiliellus olson all share a pointed snout as a common feature.
Description and Paleobiology
Skull
Schoch and Sues describe the skull of Dissorophus 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.
According to DeMar, the skull depth increases posteriorly and decreases anteriorly when in lateral view. He points out another prominent feature of Dissorophus which is an enlarged otic notch. Measuring up to 3.5 cm in length, the otic notch of Dissorophus 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.
makes a similar observation as DeMar in Broiliellus 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". DeMar mentions that the external nares is enlarged and measures up to 1 cm long in larger specimens.
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.
The orbits of Dissorophus are relatively large, circular, and oriented dorsally than laterally. As DeMar describes, the orbits are large enough to intersect with the frontals, palatines, post orbitals, lacrimals, and jugals.