|Reconstructed cast of the holotype specimen (UCMP 37302) in position of burial, Royal Ontario Museum|
Dilophosaurus (/daɪˌloʊfəˈsɔːrəs, -foʊ-/ dy-LOHF-o-SOR-əs) is a genus of theropod dinosaur that lived in what is now North America during the Early Jurassic, about 193 million years ago. Three skeletons were discovered in northern Arizona in 1940, and the two best preserved were collected in 1942. The most complete specimen became the holotype of a new species in the genus Megalosaurus, named M. wetherilli by Samuel P. Welles in 1954. Welles found a larger skeleton belonging to the same species in 1964. Realizing it bore crests on its skull, he assigned the species to the new genus Dilophosaurus in 1970, as Dilophosaurus wetherilli. The genus name means "two-crested lizard", and the species name honors John Wetherill, a Navajo councilor. Further specimens have since been found, including an infant. Footprints have also been attributed to the animal, including resting traces. Another species, Dilophosaurus sinensis from China, was named in 1993, but was later found to belong to the genus Sinosaurus.
At about 7 meters (23 ft) in length, with a weight of about 400 kilograms (880 lb), Dilophosaurus was one of the earliest large predatory dinosaurs, though it was smaller than some later theropods. It was slender and lightly built, and the skull was proportionally large, but delicate. The snout was narrow, and the upper jaw had a gap or kink below the nostril. It had a pair of longitudinal, plate-shaped crests on its skull, similar to a cassowary with two crests. The mandible was slender and delicate at the front, but deep at the back. The teeth were long, curved, thin, and compressed sideways. Those in the lower jaw were much smaller than those of the upper jaw. Most of the teeth had serrations at their front and back edges. The neck was long, and its vertebrae were hollow, and very light. The arms were powerful, with a long and slender upper arm bone. The hands had four fingers: the first was short but strong and bore a large claw, the two following fingers were longer and slenderer with smaller claws, and the fourth was vestigial. The thigh bone was massive, the feet were stout, and the toes bore large claws.
Dilophosaurus is a member of the family Dilophosauridae along with Dracovenator, a group placed between the Coelophysidae and later theropods. Dilophosaurus would have been active and bipedal, and may have hunted large animals; it could also have fed on smaller animals and fish. Due to the limited range of movement and shortness of the forelimbs, the mouth may instead have made first contact with prey. The function of the crests is unknown; they were too weak for battle, but may have been used in visual display, such as species recognition and sexual selection. It may have grown rapidly, attaining a growth rate of 30 to 35 kilograms (66 to 77 lb) per year early in life. The holotype specimen had multiple paleopathologies, including healed injuries and signs of a developmental anomaly. Dilophosaurus is known from the Kayenta Formation, and lived alongside dinosaurs such as Megapnosaurus and Sarahsaurus. Dilophosaurus was featured in the novel Jurassic Park and its movie adaptation, wherein it was given the fictional abilities to spit venom and expand a cowl on its neck, as well as being smaller than the real animal. It was designated as the state dinosaur of Connecticut in 2017.
Dilophosaurus was one of the earliest large predatory dinosaurs, a medium-sized theropod, though small compared to some of the later theropods. Slender and lightly built, its size was comparable to that of a brown bear. The largest known specimen weighed about 400 kilograms (880 lb), measured about 7 meters (23 ft) in length, and its skull was 590 millimeters (1.94 ft) long. The smaller holotype specimen weighed about 283 kilograms (624 lb), was 6.03 meters (19.8 ft) long, with a hip height of about 1.36 meters (4.5 ft), and its skull was 523 millimeters (1.716 ft) long. A resting trace of a theropod similar to Dilophosaurus and Liliensternus has been interpreted by some researchers as showing impressions of feathers around the belly and feet, similar to down. Other researchers instead interpret these impressions as