Reintroducing the Phytosaur Genus Machaeoroprosopus

I had posted about the taxonomic problem caused by the loss of the holotype specimen Machaeroprosopus validus before with a plea for people to help look for the specimen.  Come to find out a careful reading of the literature and the ICZN demonstrates that the specimen is not as important as previously believed regarding the taxonomic status of the name Machaeroprosopus. It will take awhile for Triassic and phytosaur workers to get used to using the name again and I am sure that some will just flat out refuse, but according to the ICZN the name Machaeoroprosopus is the proper one if the holotype specimen of "Belodon" buceros is truly diagnosable and if the other nominal species of "Pseudopalatus" are referable to the same genus represented by "B." buceros.

Parker, W. G., Hungerb├╝hler, A., and J. W. Martz. 2013. The taxonomic status of the phytosaurs (Archosauriformes) Machaeroprosopus and Pseudopalatus from the Late Triassic of the western United States. Earth and Environmental Science Transactions of the Royal Society of Edinburgh First View Article. DOI:

Abstract - 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.


  1. So this genus now contains seven species!?
    They really should be revised...

    1. Actually, Stocker and Butler (2013) listed Machaeroprosopus validus and M. andersoni as Phytosauria incertae sedis without commenting on their relationship to Machaeroprosopus buceros and M. pristinus in spite of the fact that M. validus is a pseudopalatine grade phytosaurid judging from the original description of Mehl (1916). And Machaeroprosopus will acquire one more species as the discovery of M. lottorum shows that Redondasaurus is congeneric with Machaeroprosopus (keep in mind that Redondasaurus bermani was recently synonymized with Redondasaurus gregorii by Spielmann and Lucas 2012)*.
      *As a side note, since Redondasaurus is congeneric with Machaeroprosopus as per the discovery of Machaeroprosopus lottorum, the presence of Redondasaurus in the lower Wingate Sandstone would make the Redonda Formation and siltstone member partially Revueltian in age because Dromomeron romeri is known from the siltstone member.

      Spielmann, J. A.& Lucas, S. G. 2012. Tetrapod Fauna of the Upper Triassic Redonda Formation, East-central New Mexico: The Characteristic Assemblage of the Apachean Land-vertebrate Faunachron. New Mexico
      Museum of Natural History and Science Bulletin, 55.

  2. Bill, Bill... haven't you been paying attention to Anchisaurus, Coelophysis, Allosaurus, Stegosaurus, etc.? We don't follow the Code, the Code follows us. The new way to handle these situations is to declare the old remains to be nomina dubia because actually studying them takes work. Then just pick a shiny new specimen as a neotype, and the popular vote makes it so. Then we can continue using the name that's currently popular and everyone's happy. Here we already had everyone using Pseudopalatus and now you've gone and messed that up. It's the same with your Typothorax/Episcoposaurus paper from that volume. You didn't see us theropod workers stoop to describing and illustrating all of Cope's Coelophysis fragments when the Rioarribasaurus situation was brought up. We just knew coelophysoids are all similar and that we wanted the Ghost Ranch taxon to be Coelophysis, so we made it so. You need to stop spending so much effort doing science and just get your desired results by fiat.

    In all seriousness though, these are both amazing papers that dinosaur workers would be wise to emulate.

    1. While the names Allosaurus, Coelophysis, Stegosaurus, and Anchisaurus have been entrenched in the public consciousness for a long time, the middle-late Norian pseudopalatines from America have had a rather unstable taxonomic history, being referred to as Phytosaurus, Rutiodon, Machaeroprosopus, Pseudopalatus, and Belodon. But the case of Machaeroprosopus is a different case than that of Allosaurus, Coelophysis, Stegosaurus, and Anchisaurus because the type specimen of Machaeroprosopus buceros is diagnostic and M. validus was tossed as a nomen dubium only because the holotype went missing several years after study, even though UW 3807 appears to be well-preserved enough to preserve diagnostic characters that would uphold the validity of M. validus. Add to that the species now included in the genera Smilosuchus were once assigned to Machaeroprosopus, but later recognized as being more primitive than Machaeroprosopus proper, Nicrosaurus, and Mystriosuchus. Some workers may object to the use of Machaeroprosopus in place of Pseudopalatus, but others will accept this name change by Parker et. al. because they know that phytosaur alpha-taxonomy has been a headache for paleontologists and that Gregory (1962) did not consider the upper Chinle phytosaurs to be distinct from Rutiodon and Phytosaurus.


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