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

Published online by Cambridge University Press:  25 September 2013

William G. Parker ,
Axel Hungerbühler  and
Jeffrey W. Martz
William G. Parker
Affiliation:
P.O. Box 2217, Petrified Forest National Park, Petrified Forest, AZ 86028, USA. Email: William_Parker@nps.gov Department of Geological Sciences, The University of Texas at Austin, Austin, TX 78712, USA
Axel Hungerbühler
Affiliation:
Mesalands Community College, Tucumcari, NM 88401, USA
Jeffrey W. Martz
Affiliation:
Denver Museum of Nature and Science, Denver, CO 80205, USA
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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.

Keywords

ICZNNorth Americataxonomytype species

Machaeroprosopus is a genus-level name applied to various phytosaur specimens from the Late Triassic of the western United States between 1916 and 1962. At its height of use, it contained eight species from a variety of stratigraphic levels in the Chinle Formation of Arizona and New Mexico (Mehl Reference Mehl, Mehl, Toepelmann and Schwartz1916, Reference Mehl1922; Camp Reference Camp1930). However, this taxonomic name is no longer in use, mainly because of the physical loss of the type specimen of the presumed type species M. validus (Gregory Reference Gregory1962; Westphal Reference Westphal1979; see history below). The genus-level name Pseudopalatus was first applied to a phytosaur specimen from Arizona by Mehl (Reference Mehl1928) and is currently considered valid with four referred species (e.g. Parker & Irmis Reference Parker and Irmis2006). In this paper we discuss the taxonomic validity of the type species of Machaeroprosopus and Pseudopalatus.

Institutional abbreviations. AMNH, American Museum of Natural History, New York; CFMNH, Field Museum of Natural History, Chicago; UCMP, University of California Museum of Paleontology, Berkeley; UM, University of Missouri, Columbia; UW, University of Wisconsin Geological Museum, Madison.

1. History

The taxonomic history of the North American members of the Pseudopalatinae, a clade of phytosaurs diagnosed by derived characters of the cranium (Ballew Reference Ballew, Lucas and Hunt1989; Hungerbühler Reference Hungerbühler2002), is complex and convoluted, but needs to be addressed to provide a framework to assess the present status of the taxonomic name Machaeroprosopus. Machaeroprosopus was erected by Mehl (Reference Mehl, Mehl, Toepelmann and Schwartz1916) in part for a skull and lower jaws from the upper part of the Chinle Formation of Arizona, M. validus (UW 3807), which was designated by Mehl (Reference Mehl, Mehl, Toepelmann and Schwartz1916) as the type species for the genus. In the same paper, Mehl (Reference Mehl, Mehl, Toepelmann and Schwartz1916, p. 23) referred the skull of “Belodon” buceros (AMNH FR 2318; Cope Reference Cope1881, Reference Cope1887, Reference Cope1888) from the Petrified Forest Member of New Mexico to Machaeroprosopus as the “second species of this genus”. Subsequently a third species, M. andersoni, was assigned to the genus by Mehl (Reference Mehl1922). This species is based on a skull (CFMNH 396, originally Walker Museum 396) most likely from the Bull Canyon Formation of New Mexico (Gregory Reference Gregory1972). The taxon Machaeroprosopus was brought to greater prominence by the assignment of five new species from the Chinle Formation of Arizona to the genus (Camp Reference Camp1930). These included M. adamanensis (UCMP 26699), M. gregorii (UCMP 27200), and M. zunii (UCMP 27036) from the Blue Mesa Member (sensu Woody Reference Woody2006), as well as M. lithodendrorum (UCMP 26688) and M. tenuis (UCMP 27018) from the Sonsela Member (Parker & Martz Reference Parker and Martz2011). Camp (Reference Camp1930) also suggested that Pseudopalatus pristinus Mehl, Reference Mehl1928 (UM 525VP) may be referable to Machaeroprosopus, a referral subsequently made by Colbert (Reference Colbert1947). Through the next few decades, other specimens (e.g. AMNH FR 3060) from the Chinle Formation and Dockum Group were referred to Machaeroprosopus (e.g. Stovall & Savage Reference Stovall and Savage1939; Colbert Reference Colbert1947).

Gregory (Reference Gregory1962) published a comprehensive overview of the phytosaurs in which he considered Machaeroprosopus to be a junior synonym of Rutiodon Emmons, Reference Emmons1856 from the eastern United States. Gregory (Reference Gregory1962) assigned species of Machaeroprosopus to both Rutiodon and the German genus Phytosaurus Jaeger, Reference Jaeger1828 (a nomen dubium that was applied mainly to specimens now assigned to Nicrosaurus O. Fraas, Reference Fraas1866), with the included species split based mainly on rostral morphology. Gregory (Reference Gregory1962) was also the first to note that the holotype specimen of M. validus (UW 3807) was lost (also see Westphal Reference Westphal1979). Unfortunately, published photographs of the original specimen do not exist (Ballew Reference Ballew, Lucas and Hunt1989).

The first numerical phylogenetic analysis of phytosaurs separated the pseudopalatine phytosaurs from Rutiodon and recognized that “Rutiodon” buceros should be assigned to Pseudopalatus Mehl, Reference Mehl1928, the type species of which is P. pristinus (Ballew Reference Ballew, Lucas and Hunt1989). This was followed by Long & Murry (Reference Long and Murry1995) who restricted Rutiodon to the eastern U.S. and considered the western U.S. “Rutiodon” species to be referable to Pseudopalatus, Leptosuchus Case, Reference Case1922 and Smilosuchus Long & Murry, Reference Long and Murry1995. In addition, to receive the species buceros, they erected the new genus name Arribasuchus Long & Murry, Reference Long and Murry1995. This taxonomy was further modified by Stocker (Reference Stocker2010) who found Leptosuchus and Smilosuchus to form two separate monophyletic clades basal to Pseudopalatinae.

Based on Mehl's (Reference Mehl, Mehl, Toepelmann and Schwartz1916) interpretive drawings of the holotype skull of M. validus (UW 3807), it has been suspected that the taxon represents a pseudopalatine phytosaur (Ballew Reference Ballew, Lucas and Hunt1989). However, because M. validus is the proposed type species (Mehl Reference Mehl, Mehl, Toepelmann and Schwartz1916), and the type specimen is lost, further referral of material to Machaeroprosopus became problematic. The most recent reviews (Ballew Reference Ballew, Lucas and Hunt1989; Long & Murry Reference Long and Murry1995) considered the genus Machaeroprosopus de facto invalid, with the consequence that it was not considered to have priority over the name Pseudopalatus. Since then, the name Machaeroprosopus has fallen out of use.

2. The status of the genus Machaeroprosopus

A careful reading of the published literature reveals, however, that the validity of the name Machaeroprosopus does not actually rely on the status of the M. validus holotype skull (UW 3807). The first pseudopalatine skull (AMNH FR 2318) described from North America is that of “Belodon” buceros (Cope Reference Cope1881, Reference Cope1887, Reference Cope1888). Subsequently, Jaekel (Reference Jaekel1910) recognised that AMNH FR 2318 was distinct from Belodon Meyer in Meyer & Plieninger, Reference Meyer and Plieninger1844 (another nomen dubium, at that time applied to species now referred to Nicrosaurus and Mystriosuchus E. Fraas, Reference Fraas1896) and provided a new generic name Metarhinus for the specimen. However, this name was preoccupied by Metarhinus Osborn, Reference Osborn1908, a brontothere. Mehl (Reference Mehl, Mehl, Toepelmann and Schwartz1916, p. 23) described a new phytosaur skull from Arizona (Machaeroprosopus validus) and wrote that “unfortunately the name proposed by Jaekel, Metarhinus, is not available and the writer would suggest the name Machaeroprosopus. Of this genus, M. validus, the form herein described may be the type. M. buceros is the second species of the genus.” Thus, in creating his new genus and assigning new and existing species, Mehl (Reference Mehl, Mehl, Toepelmann and Schwartz1916) ignored the priority of the species name M. buceros and made his new species M. validus the type for the genus, an assignment that was followed by all subsequent workers (e.g. Case Reference Case1920, Reference Case1922; Abel Reference Abel1923; Camp Reference Camp1930; Colbert Reference Colbert1947; Gregory Reference Gregory1962).

International Code of Zoological Nomenclature (ICZN) Article 67·8 states that if a replacement name is proposed for a genus name then the type species for the prior genus remains the same for its replacement genus, regardless of any contrary statement (ICZN 1999). Because B. buceros Cope, Reference Cope1881 is fixed as the type species of Metarhinus Jaekel, Reference Jaekel1910 by monotypy (ICZN article 68·3), the type species must stay the same for the first proposed replacement name, Machaeroprosopus. Thus the actual type species of Machaeroprosopus is M. buceros and not M. validus, and Mehl's (Reference Mehl, Mehl, Toepelmann and Schwartz1916) erection of M. validus as the type species is invalid. Because the type specimen of M. buceros (AMNH FR 2318) is preserved and presumably diagnosable (see Ballew Reference Ballew, Lucas and Hunt1989, p. 331), the genus is valid. We acknowledge that Hunt (Reference Hunt1994) came to the same conclusions regarding the type species of Machaeroprosopus, but did not publish his findings as a nomenclatorial act. However, M. buceros currently lacks a valid diagnosis utilising the holotype skull (AMNH FR 2318). Existing modern descriptions of this skull (Ballew Reference Ballew, Lucas and Hunt1989; Lucas et al. Reference Lucas, Heckert, Zeigler, Hunt, Heckert and Lucas2002) do not provide a differential diagnosis of M. buceros using this material, and proposed diagnoses of the species use referred material from the Canjilon Quarry of New Mexico instead (e.g. Long & Murry Reference Long and Murry1995).

The genus Pseudopalatus (type species Pseudopalatus pristinus Mehl, Reference Mehl1928) is also valid; however, in some studies P. pristinus is considered to be congeneric with Machaeroprosopus buceros (e.g. Ballew Reference Ballew, Lucas and Hunt1989; Long & Murry Reference Long and Murry1995). This relationship is supported by phylogenetic analyses where P. pristinus and M. buceros are recovered as sister taxa within the framework of a more inclusive clade (Hungerbühler Reference Hungerbühler2002; Parker & Irmis Reference Parker and Irmis2006; Hungerbühler et al. Reference Hungerbühler, Mueller, Chatterjee and Cunningham2013 (this volume)). Moreover, it has been argued that M. buceros and P. pristinus may actually represent sexual dimorphs of a single species (Colbert Reference Colbert1947; Zeigler et al. Reference Zeigler, Lucas, Heckert, Heckert and Lucas2002b). Therefore, as currently understood, Pseudopalatus is either a subjective (separate species M. buceros and P. pristinus) or an objective junior synonym (sexually dimorphic M. buceros) of Machaeroprosopus. As a consequence, all nominal species currently included in Pseudopalatus as valid taxa or synonyms should be reassigned.

2.1. Systematic palaeontology

Archosauriformes Gauthier, Kluge & Rowe, Reference Gauthier, Kluge and Rowe1988

Phytosauria Jaeger, Reference Jaeger1828, sensu Nesbitt, Reference Nesbitt2011

Phytosauridae Jaeger, Reference Jaeger1828, sensu Doyle & Sues, Reference Doyle and Sues1995

Leptosuchomorpha Stocker, Reference Stocker2010

Pseudopalatinae Long & Murry, Reference Long and Murry1995, sensu Parker & Irmis, Reference Parker and Irmis2006

Machaeroprosopus Mehl, Reference Mehl, Mehl, Toepelmann and Schwartz1916

Synonyms.Arribasuchus Long & Murry, Reference Long and Murry1995; Pseudopalatus Mehl, Reference Mehl1928

Type species. Belodon buceros Cope, Reference Cope1881

Type locality and age. Petrified Forest Member, Chinle Formation, Chama Basin, New Mexico (Cope Reference Cope1881; Lucas et al. Reference Lucas, Heckert, Zeigler, Hunt, Heckert and Lucas2002). Late Triassic, Norian, ∼212 Ma (Irmis et al. Reference Irmis, Mundil, Martz and Parker2011); Revueltian biozone (Lucas & Hunt Reference Lucas, Hunt, Lucas and Morales1993; Parker & Martz Reference Parker and Martz2011).

Referred species.Machaeroprosopus validus Mehl, Reference Mehl, Mehl, Toepelmann and Schwartz1916; Machaeroprosopus andersoni Mehl, Reference Mehl1922; Pseudopalatus pristinus Mehl, Reference Mehl1928; Machaeroprosopus tenuis Camp, Reference Camp1930; Pseudopalatus mccauleyi Ballew, Reference Ballew, Lucas and Hunt1989; Pseudopalatus jablonskiae Parker & Irmis, Reference Parker and Irmis2006; Machaeroprosopus lottorum Hungerbühler et al., Reference Hungerbühler, Mueller, Chatterjee and Cunningham2013.

Distribution and age. Sonsela, Petrified Forest, Owl Rock members, Chinle Formation, Arizona, Utah, New Mexico; Bull Canyon and Cooper Canyon Formations, Dockum Group, New Mexico, Texas, Oklahoma (Long & Murry Reference Long and Murry1995; Hunt Reference Hunt2001; Martz Reference Martz2008). Late Triassic, Norian, ∼217–∼207 Ma (Ramezani et al. Reference Ramezani, Hoke, Fastovsky, Bowring, Therrien, Dworkin, Atchley and Nordt2011; Irmis et al. Reference Irmis, Mundil, Martz and Parker2011); Revueltian biozone (Lucas & Hunt Reference Lucas, Hunt, Lucas and Morales1993; Martz Reference Martz2008; Parker & Martz Reference Parker and Martz2011).

2.2. Referral of species

Although the validity of the genus of Machaeroprosopus depends only on the validity and referral of the type species, the referral of other species to the genus as advocated here is dependent on phylogenetic relationships within the Pseudopalatinae. Pseudopalatinae (sensu Parker & Irmis Reference Parker and Irmis2006) remains a valid name for this clade regardless of the status of the genus-level name Pseudopalatus. The phylogeny of Hungerbühler (Reference Hungerbühler2002) found “Pseudopalatus” buceros, “P.” pristinus, and “P.” maccauleyi to form a clade to the exclusion of Redondasaurus, Mystriosuchus, and Nicrosaurus. Parker & Irmis (Reference Parker and Irmis2006) found “P.” jablonskiae to also fall within the “Pseudopalatus” clade. Although Stocker (Reference Stocker2010) found “Pseudopalatus” to be paraphyletic with respect to Mystriosuchus, her phylogeny only included three pseudopalatine species, and the phylogeny of Hungerbühler et al. (Reference Hungerbühler, Chatterjee and Cunningham2003) finding of “Pseudopalatus” paraphyletic with respect to “Redondasaurus” will be addressed in a forthcoming paper (Hungerbühler et al. Reference Hungerbühler, Mueller, Chatterjee and Cunningham2013 (this volume)). Until this new phylogeny incorporating multiple pseudopalatine taxa is published, we tentatively refer the above species traditionally referred to Pseudopalatus to Machaeroprosopus. Accordingly, Machaeroprosopus andersoni Mehl, Reference Mehl1922 is considered a valid taxon by some workers (e.g. Hunt Reference Hunt2001) and a junior synonym of M. pristinus by others (e.g. Long & Murry Reference Long and Murry1995) and is in need of restudy in an apomorphy-based context (e.g. Bell et al. Reference Bell, Gauthier and Bever2010) to determine its taxonomic status. Machaeroprosopus tenuis Camp, Reference Camp1930 has long been considered a junior synonym of M. pristinus by most workers (e.g. Colbert Reference Colbert1947; Ballew Reference Ballew, Lucas and Hunt1989; Long & Murry Reference Long and Murry1995) and this synonymy was even hinted at by Camp himself in Reference Camp1930; however, it is also in need to restudy to test this synonymy (Hungerbühler et al. Reference Hungerbühler, Mueller, Chatterjee and Cunningham2013 (this volume)).

None of the other species of Machaeroprosopus named by Camp (Reference Camp1930) are currently considered to fall within the genus, or even within Pseudopalatinae; these taxa have been variously referred to the genera Rutiodon, Leptosuchus, and Smilosuchus (Gregory Reference Gregory1962; Ballew Reference Ballew, Lucas and Hunt1989; Long & Murry Reference Long and Murry1995; Stocker Reference Stocker2010). Long & Murry (Reference Long and Murry1995) erected the genus Smilosuchus for “Machaeroprosopus” gregorii (UCMP 27200; Long & Murry Reference Long and Murry1995). The most recent systematic revisions of Stocker (Reference Stocker2010) considered Smilosuchus gregorii a valid taxon falling within Leptosuchomorpha but outside of Pseudopalatine, and also referred “M.” adamanensis (UCMP 26699), and “M.” lithodendrorum (UCMP 26688) to the genus Smilosuchus. Stocker (Reference Stocker2010) also found “Machaeroprosopus” zunii (UCMP 27036) and “Phytosaurus” doughtyi (AMNH 4919; Case Reference Case1920), which Camp (Reference Camp1930) tentatively assigned to Machaeroprosopus, to be non-leptosuchomorph phytosaurids, and therefore, non-pseudopalatines.

3. Discussion

Phytosaur workers may be hesitant to re-adopt a name that has not been in use since the early 1960s. Moreover, the name Machaeroprosopus in its later usage was widely identified in particular with non-pseudopalatine phytosaur species now assigned to Leptosuchus or Smilosuchus (Camp Reference Camp1930; Colbert Reference Colbert1947; Stocker Reference Stocker2010). The strongest objection might be that after decades of confusing taxonomic rearrangements, a stable consensus has been finally achieved over the last 20 years that the majority of pseudopalatine taxa from the US should be placed in the genus Pseudopalatus (e.g. Ballew Reference Ballew, Lucas and Hunt1989; Long & Murry Reference Long and Murry1995; Hunt Reference Hunt2001; Zeigler et al. Reference Zeigler, Lucas, Heckert, Heckert and Lucas2002a, Reference Zeigler, Lucas, Heckert, Heckert and Lucasb; Parker & Irmis Reference Parker and Irmis2006; Stocker Reference Stocker2010). However, we wish to point out that: (1) the species buceros is the mandatory type species for Machaeroprosopus as specified by ICZN Article 67·8; (2) to validate Pseudopalatus would require an application to the ICZN to assign a new type species, for which we see little chances for success, as a long-established name already exists for this taxon; and (3) the historical context is preserved. Machaeroprosopus is the first pseudopalatine genus erected for a species from the western US and the first three species assigned to the genus (i.e. M. validus, M. buceros, M. andersoni) are all recognised as pseudopalatine phytosaurs (Mehl Reference Mehl, Mehl, Toepelmann and Schwartz1916, Reference Mehl1922; Ballew Reference Ballew, Lucas and Hunt1989; Long & Murry Reference Long and Murry1995; Hunt Reference Hunt2001), so assigning these species to Machaeroprosopus is appropriate.

4. Acknowledgements

We thank Christian Kammerer for discussion of the ICZN, as well as Vicki Hammond and Randall Irmis for handling the manuscript. Critical reviews by Michelle Stocker and Richard Butler are appreciated and helped clarify many of the points made herein.

References

5. References

Abel, O. 1923. Die Schnauzenverletzungen der Parasuchier und ihre biologische Bedeutung. Paläontologische Zeitschrift 5, 26–57.Google Scholar
Ballew, K. L. 1989. A phylogenetic analysis of Phytosauria (Reptilia: Archosauria) from the late Triassic of the western United States. In Lucas, S. G. & Hunt, A. P. (eds) Dawn of the age of dinosaurs in the American Southwest, 309–39. Albuquerque: New Mexico Museum of Natural History and Science.Google Scholar
Bell, C. J., Gauthier, J. A. & Bever, G. S. 2010. Covert biases, circularity, and apomorphies: a critical look at the North American quaternary herpetofaunal stability hypothesis. Quaternary International 217 (1–2), 30–36.CrossRefGoogle Scholar
Camp, C. L. 1930. A study of the phytosaurs with description of new material from western North America. Memoirs of the University of California 10, 1–174.Google Scholar
Case, E. C. 1920. Preliminary description of a new suborder of phytosaurian reptiles with a description of a new species of Phytosaurus. Journal of Geology 28, 524–35.Google Scholar
Case, E. C. 1922. New reptiles and stegocephalians from the Upper Triassic of western Texas. Carnegie Institution of Washington Publication 321, 1–84.Google Scholar
Colbert, E. H. 1947. Studies of the phytosaurs Machaeroprosopus and Rutiodon. American Museum of Natural History Bulletin 88, 53–96.Google Scholar
Cope, E. D. 1881. Belodon in New Mexico. The American Naturalist 15, 922–23.Google Scholar
Cope, E. D. 1887. A contribution to the history of the Vertebrata of the Trias of North America. Proceedings of the American Philosophical Society 24, 209–28.Google Scholar
Cope, E. D. 1888. The pineal eye in extinct vertebrates. American Naturalist 24, 914–17.Google Scholar
Doyle, K. D. & Sues, H.-D. 1995. Phytosaurs (Reptilia: Archosauria) from the Upper Triassic New Oxford Formation of York County, Pennsylvania. Journal of Vertebrate Paleontology 15 (3), 545–53.Google Scholar
Emmons, E. 1856. Geological report of the midland counties of North Carolina. New York: George P. Putnam and Co. XX+352 pp.Google Scholar
Fraas, E. 1896. Die schwäbischen Trias-Saurier nach dem Material der Kgl. Naturalien-Sammlung in Stuttgart zusammengestellt. Stuttgart: Schweizerbart. 18 pp.Google Scholar
Fraas, O. 1866. Vor der Sündfluth! Eine Geschichte der Urwelt. Stuttgart: Hoffmann. 512 pp.Google Scholar
Gauthier, J. A., Kluge, A. G. & Rowe, T. 1988. Amniote phylogeny and the importance of fossils. Cladistics 4 (2), 105–209.CrossRefGoogle ScholarPubMed
Gregory, J. T. 1962. The genera of phytosaurs. American Journal of Science 260, 652–90.Google Scholar
Gregory, J. T. 1972. Vertebrate faunas of the Dockum Group, Triassic, eastern New Mexico and west Texas. New Mexico Geological Society Guidebook 23, 120–23.Google Scholar
Hungerbühler, A. 2002. The Late Triassic phytosaur Mystriosuchus westphali, with a revision of the genus. Palaeontology 45 (2), 377–418.Google Scholar
Hungerbühler, A., Chatterjee, S. & Cunningham, D. 2003. A new phytosaur species from the Triassic of West Texas: new information on cranial anatomy, taxonomy and sexual dimorphism in Pseudopalatinae. Journal of Vertebrate Paleontology 23 (Suppl. to 3), 63A.Google Scholar
Hungerbühler, A., Mueller, B., Chatterjee, S. & Cunningham, D. P. 2013. Cranial anatomy of the Late Triassic phytosaur Machaeroprosopus, with the description of a new species from west Texas. Earth and Environmental Science Transactions of the Royal Society of Edinburgh 103 (for 2012), 269–312Google Scholar
Hunt, A. P. 1994. Vertebrate paleontology and biostratigraphy of the Bull Canyon Formation (Chinle Group, Upper Triassic), east-central New Mexico with revisions of the families Metoposauridae (Amphibia: Temnospondyli) and Parasuchidae (Reptilia: Archosauria). Unpublished Ph.D. Thesis, University of New Mexico, Albuquerque. 404 pp.Google Scholar
Hunt, A. P. 2001. The vertebrate fauna, biostratigraphy and biochronology of the type Revueltian land-vertebrate faunachron, Bull Canyon Formation (Upper Triassic), east-central New Mexico. New Mexico Geological Society Guidebook 52, 123–51.Google Scholar
International Commission on Zoological Nomenclature (ICZN). 1999. International Code of Zoological Nomenclature, 4th edition. London: The International Trust for Zoological Nomenclature. 126 pp.Google Scholar
Irmis, R. B., Mundil, R., Martz, J. W. & Parker, W. G. 2011. High-resolution U–Pb ages from the Upper Triassic Chinle Formation (New Mexico, USA) support a diachronous rise of dinosaurs. Earth and Planetary Science Letters 309 (3–4), 258–67.Google Scholar
Jaeger, G. F. 1828. Über die fossilen Reptilien, welche in Würtemberg aufgefunden worden sind. Stuttgart: Metzler. 48 pp.Google Scholar
Jaekel, O. 1910. Ueber einen neuen Belodonten aus dem Buntsandstein von Bernburg. Sitzungsberichte der Gesellschaft Naturforschender Freunde zu Berlin 1910, 197–229.Google Scholar
Long, R. A. & Murry, P. A. 1995. Late Triassic (Carnian and Norian) tetrapods from the southwestern United States. New Mexico Museum of Natural History and Science Bulletin 4. Albuquerque: New Mexico Museum of Natural History and Science. 254 pp.Google Scholar
Lucas, S. G., Heckert, A. B., Zeigler, K. E. & Hunt, A. 2002. The type locality of Belodon buceros Cope, 1881, a phytosaur (Archosauria: Parasuchidae) from the Upper Triassic of north-central New Mexico. In Heckert, A. B. & Lucas, S. G. (eds) Upper Triassic stratigraphy and paleontology. New Mexico Museum of Natural History and Science Bulletin 21, 189–92. Albuquerque: New Mexico Museum of Natural History and Science. 301 pp.Google Scholar
Lucas, S. G. & Hunt, A. P. 1993. Tetrapod biochronology of the Chinle Group (Upper Triassic), western United States. In Lucas, S. G. & Morales, M. (eds) The nonmarine Triassic. New Mexico Museum of Natural History and Science Bulletin 3, 327–29. Albuquerque: New Mexico Museum of Natural History and Science. 478 pp.+59 pp.Google Scholar
Martz, J. W. 2008. Lithostratigraphy, chemostratigraphy, and vertebrate biostratigraphy of the Dockum Group (Upper Triassic), of southern Garza County, West Texas. Unpublished Ph.D. Dissertation, Texas Tech University, Lubbock, Texas, USA. 504 pp.Google Scholar
Mehl, M. G. 1916. New or little known phytosaurs from Arizona. In Mehl, M. G., Toepelmann, W. C. & Schwartz, G. M. (eds) New or little known reptiles from the Trias of Arizona and New Mexico, with notes from the fossil bearing horizons near Wingate, New Mexico. Bulletin of the University of Oklahoma, new series 103, University Studies Series 5. Norman: University of Oklahoma. 44 pp.Google Scholar
Mehl, M. G. 1922. A new phytosaur from the Trias of Arizona. Journal of Geology 30, 144–57.Google Scholar
Mehl, M. G. 1928. Pseudopalatus pristinus a new genus and species of phytosaurs from Arizona. University of Missouri Quarterly 3, 1–25.Google Scholar
Meyer, H. v. & Plieninger, T. 1844. Beiträge zur Paläontologie Württemberg's enthaltend die fossilen Wirbelthierreste aus den Triasgebilden mit besonderer Rücksicht auf die Labyrinthodonten des Keupers. Stuttgart: Schweizerbart. 131 pp.Google Scholar
Nesbitt, S. J. 2011. The early evolution of archosaurs: relationships and origin of major clades. Bulletin of the American Museum of Natural History 352, 292 pp.Google Scholar
Osborn, H. F. 1908. New or little known titanotheres from the Eocene and Oligocene. Bulletin of the American Museum of Natural History 24, 599–617.Google Scholar
Parker, W. G. & Irmis, R. B. 2006. A new species of the Late Triassic phytosaur Pseudopalatus (Archosauria: Pseudosuchia) from Petrified Forest National Park, Arizona. Museum of Northern Arizona Bulletin 62, 126–43.Google Scholar
Parker, W. G. & Martz, J. W. 2011. The Late Triassic (Norian) Adamanian-Revueltian tetrapod faunal transition in the Chinle Formation of Petrified Forest National Park, Arizona. Earth and Environmental Science Transactions of the Royal Society of Edinburgh 101 (for 2010), 231–60.CrossRefGoogle Scholar
Ramezani, J., Hoke, G. D., Fastovsky, D. E., Bowring, S. A., Therrien, F., Dworkin, S. I., Atchley, S. C., and Nordt, L. C. 2011. High-precision U-Pb zircon geochronology of the Late Triassic Chinle Formation, Petrified Forest National Park (Arizona, USA): Temporal constraints on the early evolution of dinosaurs. Geological Society of America Bulletin 123 (11–12), 2142–59.CrossRefGoogle Scholar
Stocker, M. R. 2010. A new taxon of phytosaur (Archosauria: Pseudosuchia) from the Norian (Late Triassic) Sonsela Member (Chinle Formation) in Arizona, and a critical re-evaluation of Leptosuchus Case, 1922. Palaeontology 53 (5), 997–1022.Google Scholar
Stovall, J. W. & Savage, D. E. 1939. A phytosaur in Union County, New Mexico, with notes on the stratigraphy. Journal of Geology 47, 759–66.Google Scholar
Westphal, K. W. 1979. Missing holotype Machaeroprosopus validus (Mehl, 1916). Journal of Paleontology 3, 741.Google Scholar
Woody, D. T. 2006. Revised stratigraphy of the lower Chinle Formation (Upper Triassic) of Petrified Forest National Park, Arizona. Museum of Northern Arizona Bulletin 62, 17–45.Google Scholar
Zeigler, K. E., Lucas, S. G. & Heckert, A. B. 2002a. A phytosaur skull from the Upper Triassic Snyder Quarry (Petrified Forest Formation, Chinle Group of north-central New Mexico). In Heckert, A. B. & Lucas, S. G. (eds) Upper Triassic stratigraphy and paleontology. New Mexico Museum of Natural History and Science Bulletin 21, 171–77. Albuquerque: New Mexico Museum of Natural History and Science. 302 pp.Google Scholar
Zeigler, K. E., Lucas, S. G. & Heckert, A. B. 2002b. The Late Triassic Canjilon Quarry (Upper Chinle Group, New Mexico) phytosaur skulls: evidence of sexual dimorphism in phytosaurs. In Heckert, A. B. & Lucas, S. G. (eds) Upper Triassic stratigraphy and paleontology. New Mexico Museum of Natural History and Science Bulletin 21, 179–88. Albuquerque: New Mexico Museum of Natural History and Science. 302 pp.Google Scholar