Thursday, September 8, 2016

[Paleontology • 2016] Vivaron haydeni • A New Rauisuchid (Archosauria, Pseudosuchia) from the Upper Triassic (Norian) of New Mexico Increases the Diversity and Temporal Range of the Clade

Vivaron haydeni  
 Lessner​, Stocker, Smith, Turner, Irmis & Nesbitt, 2016

 DOI: 10.7717/peerj.2336 


Rauisuchids are large (2–6 m in length), carnivorous, and quadrupedal pseudosuchian archosaurs closely related to crocodylomorphs. Though geographically widespread, fossils of this clade are relatively rare in Late Triassic assemblages. The middle Norian (∼212 Ma) Hayden Quarry of northern New Mexico, USA, in the Petrified Forest Member of the Chinle Formation, has yielded isolated postcranial elements and associated skull elements of a new species of rauisuchid. Vivaron haydeni gen. et. sp. nov. is diagnosed by the presence of two posteriorly directed prongs at the posterior end of the maxilla for articulation with the jugal. The holotype maxilla and referred elements are similar to those of the rauisuchid Postosuchus kirkpatricki from the southwestern United States, but V. haydeni shares several maxillary apomorphies (e.g., a distinct dropoff to the antorbital fossa that is not a ridge, a straight ventral margin, and a well defined dental groove) with the rauisuchid Teratosaurus suevicus from the Norian of Germany. Despite their geographic separation, this morphological evidence implies a close phylogenetic relationship between V. haydeni and T. suevicus. The morphology preserved in the new Hayden Quarry rauisuchid V. haydeni supports previously proposed and new synapomorphies for nodes within Rauisuchidae. The discovery of Vivaron haydeni reveals an increased range of morphological disparity for rauisuchids from the low-paleolatitude Chinle Formation and a clear biogeographic connection with high paleolatitude Pangea.

Figure 2: Holotype right maxilla of Vivaron haydeni gen. et. sp. nov. (GR 263) in (A) lateral and (B) medial views (with interpretive drawings).
 Abbreviations: a, articulation; al, alveolus; aof, antorbital fenestra; aofo, antorbital fossa; ap, ascending process; dg, dental groove; for, foramen; fos, fossa; idp, interdental plate; j, jugal; pal, palatine; *indicates autapomorphy. Scale bar  = 5 cm.    DOI: 10.7717/peerj.2336 

Systematic Paleontology

ARCHOSAURIA Cope, 1870 sensu Gauthier & Padian, 1985
SUCHIA Krebs, 1974 sensu Sereno, 1991
RAUISUCHIDAE von Huene, 1942 sensu Nesbitt, 2011

Vivaron haydeni gen. et sp. nov.

Derivation of name: Vivaron, named for the mythical 30-foot rattlesnake demon believed to haunt Orphan Mesa at Ghost Ranch (Poling-Kempes, 2005); haydeni, in honor of John Hayden, who discovered the Hayden Quarry from which the type and referred material was collected.

Holotype: right maxilla (GR 263).
Referred material: left premaxilla (GR 391), left maxilla (GR 186), left jugal (GR 641), right quadrate (GR 639), right ectopterygoid (GR 640), right ectopterygoid (GR 451). We tentatively refer to this taxon a right ilium (GR 638), right ilium (GR 642), tooth (GR 560), tooth (GR 664).

Type Horizon: Petrified Forest Member, Chinle Formation (Late Triassic: middle Norian, ∼212 Ma) (Irmis et al., 2011).

Type Locality: Hayden Quarry 2 paleochannel, Ghost Ranch, Rio Arriba County, New Mexico, USA. Referred material is from Hayden Quarry paleochannels 2, 3, and 4; all three paleochannels are geographically within 30 m of each other and stratigraphically within 15 m of each other (Fig. 1).

Emily J. Lessner​, Michelle R. Stocker, Nathan D. Smith, Alan H. Turner, Randall B. Irmis and Sterling J. Nesbitt. 2016. A New Rauisuchid (Archosauria, Pseudosuchia) from the Upper Triassic (Norian) of New Mexico Increases the Diversity and Temporal Range of the Clade. PeerJ. 4:e2336. DOI: 10.7717/peerj.2336

Undergraduate researcher leads study naming a new species of reptile from 212 million years ago