Dilophosaurus wetherilli

Dilophosaurus wetherilli was an early large-bodied theropod from the Kayenta Formation of northern Arizona. At roughly seven metres long, it was among the largest North American land animals of its time. Two tall, parallel nasolacrimal crests rose above its skull, while a deep snout, recurved serrated teeth, strong neck, grasping hands and powerful hind limbs equipped it as an active macropredator. A comprehensive 2020 redescription united five skeletons as one species and placed it outside both Coelophysoidea and Ceratosauria, near the stem leading toward later averostran theropods.

Its fossils occur between approximately 193 and 183 million years ago. Values shown here are approximate and reflect the current curated seed dataset.

Each head crest was a compound structure involving the premaxilla, nasal and lacrimal bones and connecting with air spaces in the snout. The crests were too thin for forceful combat and probably contributed to visual display or species recognition, although colour and exact function are unknown. The neck and trunk vertebrae contain hollows and bony partitions associated with an air-sac respiratory system. The arms were not useless: the shoulder and forelimb were robust, the first three fingers were well developed and clawed, and a fourth digit was reduced. The skull's joints were more firmly connected than older weak-jawed reconstructions suggested.

• Pair of tall, thin nasolacrimal crests built from several skull bones
• Deep snout with firmly connected tooth-bearing bones
• Recurved, laterally compressed teeth with serrated cutting edges
• Long neck with air-filled vertebrae linked to a bird-like air-sac system
• Strong shoulders and grasping hands with three functional clawed fingers
• Reduced fourth manual digit retained beside the functional fingers
• Powerful hind limbs and a long counterbalancing tail

Jesse Williams, a Navajo man, discovered the first two skeletons near Tuba City in 1940 and brought the site to the attention of Samuel P. Welles and the University of California Museum of Paleontology. Welles's team excavated them in 1942. He named the species Megalosaurus wetherilli in 1954, honouring local explorer John Wetherill. A third skeleton found in 1964 preserved enough of the skull to reveal the paired crests, leading Welles to establish the genus Dilophosaurus in 1970. Later fieldwork by Timothy Rowe's teams recovered two more individuals, including a juvenile. All known specimens held in Berkeley and Austin remain the property of the Navajo Nation.

Discovery credit: Jesse Williams, Samuel P. Welles.

Naming authors: Samuel P. Welles.

Dilophosaurus lived on the broad river plains and sandy channels recorded by the silty facies of the Kayenta Formation. The Early Jurassic landscape of what is now northern Arizona included seasonal waterways, dunes and patches of vegetation. It shared the region with the sauropodomorph Sarahsaurus, armoured Scelidosaurus-like herbivores, smaller theropods, crocodylomorphs, turtles and early mammals. The fossil region lies within the Navajo Nation, and the marker on the map is deliberately regional rather than an excavation coordinate.

Its size, teeth, reinforced snout, strong neck and grasping forelimbs identify Dilophosaurus as an active predator capable of handling substantial prey. Bite marks and shed theropod teeth occur with herbivore remains in the Kayenta Formation, but they do not preserve a complete hunting event or identify every feeder with certainty. The twin crests were probably visual signals rather than weapons. There is no fossil evidence for venom glands, projectile venom or an expandable neck frill, and no evidence that the animal regularly hunted in coordinated packs.

• The two crests that give Dilophosaurus its name were not recognised when the first fragmentary skulls were described, so the species initially entered science as Megalosaurus wetherilli.
• The real animal was about seven metres long—roughly twice the length of the small Dilophosaurus portrayed in Jurassic Park.
• No fossil supports the film version's neck frill or venom; both were invented for storytelling.
• Holotype UCMP 37302 preserves abnormalities in eight shoulder or forelimb bones, including healed fractures and infections, showing that the animal survived for months and possibly years after serious injuries began.
• The five scientifically described skeletons housed in California and Texas remain the property of the Navajo Nation.

A research repository is not necessarily a public exhibit. Loan and display status can change, so check with the institution before visiting.

1. 01
   The Paleobiology Database

   Open source
2. 02
   A comprehensive anatomical and phylogenetic evaluation of Dilophosaurus wetherilli (Dinosauria, Theropoda) with descriptions of new specimens from the Kayenta Formation of northern Arizona

   Adam D. Marsh, Timothy B. Rowe · Journal of Paleontology 94, Memoir 78 · 2020

   Open source
3. 03
   Towards a more complete understanding of the meat-eating dinosaur Dilophosaurus wetherilli

   Adam D. Marsh · Cambridge Core Blog · 2020

   Open source
4. 04
   Record-Breaking Pain: The Largest Number and Variety of Forelimb Bone Maladies in a Theropod Dinosaur

   Phil Senter, Sara L. Juengst · PLOS ONE · 2016

   Open source