‘Francosuchus’ trauthi is not Paleorhinus: implications for Late Triassic vertebrate biostratigraphy

ABSTRACT

A rostrum fragment from the marginal marine upper Lunz Formation of Austria (early Late Triassic: late Carnian) was previously identified as a new species of phytosaurian archosauriform, ‘Francosuchus’ trauthi. ‘Francosuchus’ trauthi was subsequently synonymized with the non-phytosaurid phytosaur Paleorhinus, and this synonymy was used as evidence to correlate the ‘Paleorhinus biochron’ and the Otischalkian land-vertebrate faunachron to the marine timescale. Here, I provide a redescription of ‘Francosuchus’ trauthi and document anatomical features that differ substantially from all known species of non-phytosaurid phytosaur. There is no evidence to support synonymy of ‘Francosuchus’ trauthi with Paleorhinus, and no unambiguous features to support a phytosaurian identification. However, ‘Francosuchus’ trauthi possesses a unique combination of characters that distinguish it from all other Triassic tetrapods, and necessitates referral of the species to a new genus, Dolerosaurus, gen. nov. Rejection of the proposed synonymy between ‘Francosuchus’ trauthi and Paleorhinus means that the ‘Paleorhinus biochron’ cannot be tied to the marine late Carnian as previously suggested, and provides further evidence of the problems inherent in attempting to correlate the terrestrial Triassic to the marine timescale.

ACKNOWLEDGMENTS

This work was supported by a DFG Emmy Noether Programme award (BU 2587/3-1). I thank U. Göhlich (NHMW) and P. Havlik (University of Tübingen) for access to specimens in their care, R. Stepanek (University of Vienna) and M. Dobritz (Klinikum rechts der Isar, Munich) for CT scanning, and S. Lautenschlager for assistance with CT data. C. Kammerer provided invaluable assistance with etymological matters, suggesting the new generic name used here. This work benefited from discussions with M. Jones, M. Stocker, R. Bronowicz, O. Rauhut, P. Barrett, J. Müller, and T. Scheyer. The review comments of M. Stocker and W. Parker and the editorial work of R. Irmis helped improve the final version of the manuscript.

Handling editor: Randall Irmis.