Abstract

The phylogeny of the largest amphibians, the Triassic capitosaurs, is still much debated. One key taxon for the understanding of their relationships, Odenwaldia heidelbergensis from the Buntsandstein of Waldkatzenbach, is restudied here. A phylogenetic analysis performed on the basis of 66 characters and 25 taxa gives a new hypothesis of relationships. It rests to a large degree on previous data matrices, but many character codings have been changed with respect to new observations as well as the discovery of new taxa. The present data indicate that all classic capitosaur taxa do form a clade.
The Capitosauria (all taxa more closely related to Parotosuchus than to Trematosaurus) excludes Benthosuchus and Edingerella but includes Wetlugasaurus, Sclerothorax, Watsonisuchus, Parotosuchus, and all other capitosaurs. All capitosaurs above Watsonisuchus are referred to as the Capitosauroidea, which includes Parotosuchus, Cherninia + Odenwaldia, Eryosuchus, Xenotosuchus, and a vast capitosaur crown clade. The crown includes two main branches: (1) the “Eucyclotosauria” (Cyclotosaurus, Kupferzellia, Procyclotosaurus, Stanocephalosaurus pronus) and (2) the “Paracyclotosauria” (Stanocephalosaurus birdi, Paracyclotosaurus, Mastodonsaurus, and the heylerosaurids Eocyclotosaurus and Quasicyclotosaurus). Stratigraphically, capitosaur phylogeny still reveals a rather poor match. However, the present phylogenetic hypothesis matches the stratigraphic ranges more precisely than the previous ones. The early branching between the “Eucyclotosauria” and “Paracyclotosauria” is more consistent with the fossil record than an alternative concept, in which Cyclotosaurus and the heylerosaurids form sister taxa (“Pancyclotosauria”). In any case, the otic fenestra and
several other probably correlated features in the palate must have evolved two times independently within the crown
capitosauroids