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A New Rauisuchid (Archosauria, Pseudosuchia) From the Upper Triassic (Norian) of New Mexico Increases the Diversity and Temporal Range of the Clade

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A New Rauisuchid (Archosauria, Pseudosuchia) From the Upper Triassic (Norian) of New Mexico Increases the Diversity and Temporal Range of the Clade

Emily J Lessner et al. PeerJ.

Abstract

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.

Keywords: Hayden Quarry; Postosuchus; Rauisuchidae; Teratosaurus.

Conflict of interest statement

The authors declare that they have no competing interests.

Figures

Figure 1
Figure 1. Stratigraphic and geographic location of the Hayden Quarry.
(A) Stratigraphic section showing the location of major Ghost Ranch vertebrate fossil sites (adapted from Whiteside et al., 2015), (B) Map of New Mexico with Triassic exposures in grey (adapted from Irmis et al., 2011), and (C) Locality photo of the Hayden Quarry showing the relative locations of paleochannels 2, 3, and 4. Abbreviations: CaQ, Canjilon Quarry; CoQ, Coelophysis Quarry; H2, Hayden Quarry 2; H3, Hayden Quarry 3; H4, Hayden Quarry 4; SQ, Snyder Quarry.
Figure 2
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.
Figure 3
Figure 3. Left lateral views and interpretive drawings of the maxillae of (A) Batrachotomus kupferzellensis (SMNS 52970), (B) Fasolasuchus tenax (PVL 3851), (C) Polonosuchus silesiacus (ZPAL AbIII/563), (D) Postosuchus kirkpatricki (TTU-P 9000), (E) Teratosaurus suevicus (NHMUK 38646; reversed), and (F) Vivaron haydeni gen. et. sp. nov. (GR 263; reversed) emphasizing the antorbital fossa.
Scale bars = 5 cm.
Figure 4
Figure 4. 3D visualization of CT scan data of holotype right maxilla of Vivaron haydeni gen. et. sp. nov. (GR 263) in (A) lateral and (B) medial views with bone depicted in gray, teeth in yellow, and trigeminal nerve pathway in blue.
Scale bar = 5 cm.
Figure 5
Figure 5. Referred left maxilla of Vivaron haydeni gen. et. sp. nov. (GR 186) in (A) anterior, scale bar = 1 cm (B) lateral, and (C) medial views.
Abbreviations: a, articulation; al, alveolus; al.for, anterolateral foramen; am.fos, anteromedial fossa; ap, ascending process; dg, dental groove; for, foramen; idp, interdental plate; j, jugal; mxp, palatal process of the maxilla; pm, premaxilla; snf, subnarial fenestra; *indicates potential autapomorphy. Scale bar = 1 cm in (A) and 5 cm in (B) and (C).
Figure 6
Figure 6. Referred left premaxilla of Vivaron haydeni gen. et. sp. nov. (GR 391) in (A) medial, (B) lateral, and (C) ventral views (with interpretive drawings).
Abbreviations: a, articulation; adp, anterodorsal process; al, alveolus; en, external naris; for, foramen; fos, fossa; idp, interdental plate; pdp, posterodorsal process; pm, premaxilla; pmxp, premaxillary protuberance; snf, subnarial fenestra; *indicates potential autapomorphy. Scale bar = 1 cm.
Figure 7
Figure 7. Referred cranial elements of Vivaron haydeni gen. et. sp. nov. Left jugal (GR 641) in (A) medial and (B) lateral views; right ectopterygoid (GR 640) in (C) dorsal and (D) lateral views; right ectopterygoid (GR 451) in (E) dorsal and (F) lateral views; tooth (GR 560) (G); tooth (GR 664) (H) and wrinkled enamel (I).
Abbreviations: a, articulation; ec, ectopterygoid; g, groove; j, jugal; pt, pterygoid; rr, rugose ridge. Scale bars = 1 cm; arrows point anteriorly.
Figure 8
Figure 8. Referred right quadrate of Vivaron haydeni gen. et. sp. nov. (GR 639) in (A) anterior, (B) medial, and (C) posterior views (with interpretive drawings).
Abbreviations: a, articulation; co, condyle; cr, crest; dlp, dorsolateral process; fos, fossa; g, groove; pt, pterygoid; ptw, pterygoid wing; qf, quadrate foramen; qj, quadratojugal; sq, squamosal; *indicates potential autapomorphy. Scale bar = 5 cm.
Figure 9
Figure 9. Referred right ilia of Vivaron haydeni gen. et. sp. nov. GR 638 in (A) dorsal, (B) lateral, and (C) medial views; GR 642 in (D) dorsal, (E) lateral, and (F) medial views.
Abbreviations: a, articulation; ac, acetabulum; d, depression; f, flange; ip, ischial peduncle of the ilium; pap, preacetabular process; pbp, pubic peduncle of the ilium; pp, postacetabular process; sac, supra-acetabular crest; sar, supra-acetabular ridge; sr, sacral. Scale bar = 5 cm.
Figure 10
Figure 10. Strict consensus of Archosauria (80 taxa, 412 characters) highlighting relationships of Vivaron haydeni gen. et. sp. nov. within Rauisuchidae.
Consensus of 3,240 MPTs of length 1,287. Circles = nodes; chevrons = stem groups.
Figure 11
Figure 11. Distribution of Rauisuchidae across Pangea during the Late Triassic with each star marking a locality where rauisuchid material has been confirmed (25 stars present in the southwestern United States; generated from http://fossilworks.org/).
The underlying source of the data is the Paleobiology Database (http://www.paleobiodb.org).

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Further reading

    1. Alcober O. Redescription of the skull of Saurosuchus galilei (Archosauria: Rauisuchidae) Journal of Vertebrate Paleontology. 2000;20(2):302–316. doi: 10.1671/0272-4634(2000)020[0302:ROTSOS]2.0.CO;2. - DOI
    1. Brusatte SL, Benton MJ, Ruta M, Lloyd GT. Superiority, competition, and opportunism in the evolutionary radiation of dinosaurs. Science. 2008;321(5895):1485–1488. doi: 10.1126/science.1161833. - DOI - PubMed
    1. Chatterjee S. Postosuchus, a new thecodontian reptile from the Triassic of Texas and the origin of tyrannosaurs. Philosophical Transactions of the Royal Society of London Series B, Biological Sciences. 1985;309(1139):395–460. doi: 10.1098/rstb.1985.0092. - DOI
    1. Drumheller SK, Stocker MR, Nesbitt SJ. Direct evidence of trophic interactions among apex predators in the Late Triassic of western North America. Naturwissenschaften. 2014;101(11):975–987. doi: 10.1007/s00114-014-1238-3. - DOI - PubMed
    1. Heckert AB, Lucas SG. Triassic vertebrate paleontology in New Mexico. New Mexico Museum of Natural History and Science Bulletin. 2015;68:77–96.

Grant support

Funding for this project was provided by NSF grants EAR—134950, 1349554, 1349667, and 1349654 and National Geographic Society Research Grant # 8014-06 (awarded to K. Padian). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

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