A new species of Cyclotosaurus (Stereospondyli, Capitosauria) from the Late Triassic of Bielefeld, NW Germany, and the intrarelationships of the genus

Article, Other literature type English OPEN
Witzmann, Florian ; Sachs, Sven ; Nyhuis, Christian J. (2016)
  • Publisher: Copernicus Publications
  • Journal: (issn: 2193-0074, eissn: 2193-0074)
  • Related identifiers: doi: 10.5194/fr-19-83-2016
  • Subject: Paleontology | QE701-760

A nearly complete dermal skull roof of a capitosaur stereospondyl with closed otic fenestrae from the middle Carnian Stuttgart Formation (Late Triassic) of Bielefeld-Sieker (NW Germany) is described. The specimen is assigned to the genus <i>Cyclotosaurus</i> based on the limited contribution of the frontal to the orbital margin via narrow lateral processes. A new species, <i>Cyclotosaurus buechneri</i> sp. nov., is erected based upon the following unique combination of characters: (1) the interorbital distance is short so that the orbitae are medially placed (shared with <i>C. robustus</i>); (2) the region lateral to the orbitae is only slightly broader than the orbitae (shared with <i>C. posthumus</i>, <i>C. ebrachensis</i>, <i>C. intermedius</i>, and <i>C. mordax</i>); (3) the postorbital region is slender (shared with <i>C. ebrachensis</i>); (4) the preorbital projection of the jugal is shorter than half the length of the snout (shared with <i>C. mordax</i>, <i>C. ebrachensis</i>, <i>C. intermedius</i>, <i>C. posthumus</i>, and <i>C. hemprichi</i>). A phylogenetic analysis of seven <i>Cyclotosaurus species</i>, including <i>C. buechneri</i>, and eight further capitosaur taxa with the Rhinesuchidae as an outgroup finds a monophyletic <i>Cyclotosaurus</i>. In accordance with its stratigraphic occurrence, <i>C. buechneri</i> nests at its base but is more derived than <i>C. robustus</i>. Among the more derived <i>Cyclotosaurus</i> species, <i>C. ebrachensis</i> and <i>C. intermedius</i>, as well as <i>C. posthumus</i> and <i>C. hemprichi</i>, form sister groups, respectively. However, the phylogenetic position of <i>C. mordax</i> with respect to both groups remains unresolved. In the phylogenetic analysis presented here, <i>Cyclotosaurus</i> is the sister group of the Heylerosaurinae (<i>Eocyclotosaurus</i> + <i>Quasicyclotosaurus</i>). <i>Cyclotosaurus buechneri</i> represents the only unequivocal evidence of <i>Cyclotosaurus</i> (and of a cyclotosaur in general) in northern Germany.
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