A comprehensive anatomical and phylogenetic evaluation of Dilophosaurus wetherilli (Dinosauria: Theropoda) with descriptions of new specimens from the Kayenta Formation of northern Arizona

Dilophosaurus wetherilli was the largest animal known to have lived on land in North America during the Early Jurassic. Despite its charismatic presence in pop culture and dinosaurian phylogenetic analyses, major aspects of the skeletal anatomy, taxonomy, ontogeny, and evolutionary relationships of this dinosaur remain unknown. Skeletons of this species were collected from the middle and lower part of the Kayenta Formation in the Navajo Nation of Arizona. Redescription of the holotype, referred, and previously undescribed specimens of Dilophosaurus wetherilli supports the existence of a single species of crested, large-bodied theropod in the Kayenta Formation. The parasagittal nasolacrimal crests are uniquely constructed by a small ridge on the nasal process of the premaxilla, dorsoventrally-expanded nasal, and tall lacrimal that includes a posterior process behind the eye. The cervical vertebrae exhibit serial variation within the posterior centrodiapophyseal lamina, which bifurcates and reunites down the neck. Iterative specimen-based phylogenetic analyses result in each of the additional specimens recovered as the sister taxon to the holotype. When all five specimens are included in an analysis, they form a monophyletic group that supports the monotypy of the genus. Dilophosaurus wetherilli is not recovered as a ceratosaur or coelophysoid but is instead a non-averostran neotheropod in a grade with other stem-averostrans like Cryolophosaurus ellioti and Zupaysaurus rougieri. We do not recover a monophyletic 'Dilophosauridae.' Instead of being apomorphic for a small clade of early theropods, it is more likely that elaboration of the nasals and lacrimals of stem-averostrans is plesiomorphically present in early ceratosaurs and tetanurans that share those features. Many characters of the axial skeleton of Dilophosaurus wetherilli are derived compared to Late Triassic theropods and may be associated with macropredation and an increase in body size in Theropoda through the Triassic-Jurassic boundary.The UCMP, MNA, and TMM specimens in this study are property of the Navajo Nation and are held in trust at the University of California Museum of Paleontology (Berkeley, CA), the Museum of Northern Arizona (Flagstaff, AZ), and the Texas Vertebrate Paleontology Collections at The University of Texas at Austin (Austin, TX). Please acknowledge the Navajo Nation when referring to these specimens. Any persons wishing to conduct geologic investigations on the Navajo Nation must first apply for and receive a permit from, P.O. Box 1910, Window Rock, AZ 86515 and telephone number (928) 871-6587.Funding provided by: National Science FoundationCrossref Funder Registry ID: http://dx.doi.org/10.13039/100000001Award Number: CNS-0709135Funding provided by: Geology Foundation, University of Texas at AustinCrossref Funder Registry ID: http://dx.doi.org/10.13039/100006776Award Number: Funding provided by: University of California Museum of PaleontologyCrossref Funder Registry ID: http://dx.doi.org/10.13039/100011068Award Number: Funding provided by: National Science FoundationCrossref Funder Registry ID: http://dx.doi.org/10.13039/100000001Award Number: EAR-0948842Funding provided by: National Science FoundationCrossref Funder Registry ID: http://dx.doi.org/10.13039/100000001Award Number: EAR-1160721Funding provided by: National Science FoundationCrossref Funder Registry ID: http://dx.doi.org/10.13039/100000001Award Number: EAR-1258878Funding provided by: National Science FoundationCrossref Funder Registry ID: http://dx.doi.org/10.13039/100000001Award Number: EAR-1561622Supplemental Data 1: Linear measurements less than 200 mm were measured using Pittsburgh electronic digital calipers. Lengths longer than 200 mm were measured using a paper tape measure. All measurements are in mm unless otherwise noted. Measurements with * denote those taken off of broken surfaces and should be considered minimum distances. When two numbers are present, the first represents the left side and the second represents the right. A single number results from midline elements or the only preserved element in that specimen. See description for details. Supplemental Data 2: Character descriptions for the phylogenetic analyses. Supplemental Data 3: The braincase of TMM 47006-1 was scanned at the University of Texas High-Resolution X-ray CT Facility using a North Star Imaging scanner that comprises a Fein Focus High Power 200 kV source (0.24 mA), aluminum filter, and Perkin Elmer detector. The voxel size was 50.5 microns, resulting in 1733 total slices. A post-reconstruction ring correction was applied to slices 1420-1733. Segmentation, image processing, and surface-file editing were accomplished using VGStudio Max (version 2.0.1) and Meshmixer (version 3.3.15). Supplemental Data 4: TNT file for the phylogenetic analyses. Supplemental Data 5: TNT outputs for the six phylogenetic analyses (MPTs, apomorphy lists, consensus trees, and support values)