Earth and Environmental Science Transactions of the Royal Society of Edinburgh


The taxonomic status of the phytosaurs (Archosauriformes) Machaeroprosopus and Pseudopalatus from the Late Triassic of the western United States

William G. Parkera1a2, Axel Hungerbühlera3 and Jeffrey W. Martza4

a1 P.O. Box 2217, Petrified Forest National Park, Petrified Forest, AZ 86028, USA. Email:

a2 Department of Geological Sciences, The University of Texas at Austin, Austin, TX 78712, USA

a3 Mesalands Community College, Tucumcari, NM 88401, USA

a4 Denver Museum of Nature and Science, Denver, CO 80205, USA


The genus Machaeroprosopus has long been considered invalid because the type specimen of the Late Triassic phytosaur species, M. validus, has been lost. Re-examination of the primary literature regarding the establishment of the Late Triassic phytosaur genus Machaeroprosopus demonstrates that M. buceros is the correct type species, not M. validus. Thus, the genus level name Machaeroprosopus has priority over the genera Pseudopalatus and Arribasuchus and all nominal species should be reassigned. Reassignment of these species to Machaeroprosopus satisfies the requirements of the International Code of Zoological Nomenclature (ICZN) and preserves historical context. The name Pseudopalatinae is retained as the valid clade name for these phytosaurs because its usage falls outside of the ICZN.

(Received January 12 2012)

(Accepted December 06 2012)


  • ICZN;
  • North America;
  • taxonomy;
  • type species