Sclerocephalus - Phylogeny

Phylogeny

The phylogenetic relationships of Sclerocephalus are uncertain. It was traditionally considered a close relative of the genus Onchiodon, and both were placed in the family Actinodontidae. Actinodontidae was thought to be closely related to the family Eryopidae, and is now considered a synonym of that group. However, while Sclerocephalus shares some similarities with eryopids, it also shares much in common with a group of large-bodied, semiaquatic temnospondyls called Stereospondylomorpha. Sclerocephalus and Onchiodon are no longer thought to be closely related, and while Onchiodon remains a close relative of eryopids, Sclerocephalus is often grouped near the genus Archegosaurus as a basal stereospondylomorph.

The most commonly accepted phylogeny of temnospondyls (first proposed by Yates and Warren ) divides the group into two different branches called Limnarchia and Euskelia. Limnarchia is a diverse Mesozoic clade that includes Stereospondylomorpha. Euskelia is a smaller Paleozoic clade that includes Eryopidae and the group Dissorophoidea, which may have given rise to modern amphibians. An earlier phylogeny proposed by Boy (1990) takes a different view, combining Eryopidae and Stereospondylomorpha into the group Eryopoidea, with dissorophoids as distant relatives. If this phylogeny is correct, Sclerocephalus would be a basal member of Eryopoidea, close to the ancestry of most other stereospondylomorphs.

Schoch & Witzmann (2009) found support for the Eryopoidea clade. They included Sclerocephalus in their phylogenetic analysis and found it to nest at the base of Stereospondylomorpha. Below is a cladogram from their study: