Diplocaulus

Credit: Entelognathus on the Wikimedia Commons.

*Diplocaulus* is an extinct genus of lepospondyl that lived in North America and Africa during the Late Carboniferous to the Late Permian.

## History

*D. salamandroides* is the type species of *Diplocaulus*, found near Danville, Illinois by Willian Gurley and J.C. Winslow. They were described by Edward Drinker Cope (1877), from several vertebrae sent to him by the discoverers. They were noted to be similar to salamanders (hence the chosen epithet), but Cope decided not to further classify them. A labyrinthodont mandible with teeth was associated with these vertebrae, but it was much larger, so it likely belongs to *Eryops* or another larger species of amphibian. It can be distinguished from D. magnicornis by its small size and less pronounced accessory articular processes. They were found in rocks known as the "*Clepsydrops* shales", believed to be Missourian-aged.

*D. magnicornis* was named by Cope (1882), being the most common and well-described *Diplocaulus* by far. It is also the first species known from more than vertebrae, allowing scientists to pin the true appearance of *Diplocaulus*. Much modern knowledge is known from *D. magnicornis* since it outnumbers all *Diplocaulus* in terms of known material. *D. magnicornis* lived in the red beds in Texas and Oklahoma.

*D. brevirostris*, though rarer, is similar to *D. magnicornis*, represented by some specimens from the early Texas red beds strata  of the Arroyo Formation, Clear Fork Group. It was differentiated by a much shorter, blunterrostrum with more elongate horns with a convex upper surface on the parietals and a strong, smooth curve at the posterior of the skull. Though juvenile *D. magnicornis* have a similar edge on the rear of their skull, but *D. brevirostris* are clearly mature because of their robust ornamentation. Thus, they are considered different. AM 4470 is the only specimen known from more than a skull, preserves vertebrae similar to *"D. primigenius"*. E.C. Olson, who described the species, suggested it lived in a different environment from *D. magnicornis*, which accounts for their comparative rarity. However, it has been suggested *D. magnicornis* lived in similar environments, so this is now seen as incorrect.

*D. recurvatus* is known from the Texas red beds, Vale Formation and is very similar to *D. magnicornis*, partially coexisting in younger layers. Olson hypothesized it may have descended from an early *D. magnicornis* population It differs from the tips of the horns bending and abruptly tapering. Comparisons between *D. magnicornis* indicates that they had developmental pathways that differed from *D. magnicornis*. The skull length and width seem to inversely correlate in *D. recurvatus* and directly in *D. magnicornis*. Additionally, the restricted horns develops in *D. recurvatus* where they would expand in *D. magnicornis*.

*D. minimus*, known from the Ikakern Formation of Morocco, has an unusually asymmetrical cranium with a long left prong and short, rounder right prong. This is present in many referred skulls, so it is unlikely to be caused by distortion or crushing. Some studies suggest the species is closer related to *Diploceraspis* than to *D. magnicornis*. This may suggest *Diplocaulus* is not a truly monophyletic genus, and that *Diploceraspis* is a junior synonym or *"D." minimus* is a distinct genus.

## Description

The boomerang shaped skull were either used for buoyancy or as gills. *Diplocaulus* had four small limbs, but were hardly used, preferring to swim in swamps rather than walk on land. The body of *Diplocaulus* is very salamander-like. Although no tails of *Diplocaulus* are assigned, a row of tail vertebrae near it's head, from a nearly complete and articulated specimen in 1917. This is interpreted as a long slender tail, which could curl towards the animal's head when curled in a ball. Research since discovery has disputed whether the anguiliform tail was the main source of propulsion. *Diplocaulus* is known for two long tubular protrusions from the skull, which shaped like a boomerang. Most of the outer-front edge of the two formations is lined by an elongated and blade-like squamosal. However, the rear edge is formed by the postparietal, which is named the dermosupraoccipitals in older publishing. Each horn from base to tip is comprised of a long bone that has a history with uncertain identification. Many sources state the bone is a tabular, which lies at the rear edge of the skull in early tetrapods. In 1951, Olson claims it could not be a tabular because it contacts the parietals at a point, which true tabulars do not. He argues it is a supratemporal bone, which enlarges and drifts to the rear tip of the skull. Beerbower in 1963 counters Olson's claims that Urocordylus retains both bones, and the tabular sits in a similar position touching the parietals near the skull's rear. Based upon this, the bone is likely a tabular, and newer sources use Beerbower's point.

## Paleoecology

Three juvenile *Diplocaulus* in a burrow containing eight animals (including a juvenile *Eryops*) were found partially eaten by *Dimetrodon*, who probably unearthed the amphibians during a drought. One was killed by a bite to the head that took a part of the skull and brain, a fatal injury the animal could not defend against.

## Species

* *D. salamandroides*
* *D. magnicornis*
* *D. brevirostris*
* *D. recurvatus*?
* "*D. "minimus*?

## Synonyms

### Genus Synonymy

* *Permoplatyops*
* *Diploceraspis*?

### Species Synonymy

* *D. limbatus* (=*D. brevirostris*)
* *D. copei* (=*D. magnicornis*)
* *D. pusillus*? (=D*. magnicornis*)
* *D. primigenius* (=*D. magnicornis*)
* *D. parvus* (=*D. recurvatus*)

## References

https://en.wikipedia.org/wiki/Diplocaulus