Dilophosaurus is a genus of theropod dinosaurs that lived in what is now North America during the Early Jurassic, about 193 million years ago.

A Navajo man named Jesse Williams found the first Dilophosaurus specimens in 1940 on Navajo Nation land near Tuba City, Arizona. In 1942, Williams showed the fossils to paleontologists from the University of California, Berkeley, including Samuel Welles, who named it as a new species in 1954.

The genus name is derived from the Greek words di meaning "two", lophos meaning "crest", and sauros meaning "lizard"--a reference to the pair of longitudinal, arched crests on its skull. 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.

In 1954, Welles described Dilophosaurus as a new species in the existing genus Megalosaurus, but revised his opinion in 1970 after discovering that it had crests. At the time, Megalosaurus was used as a "wastebasket taxon", wherein many species of theropods were placed, regardless of their geologic age or locality.

At about 7 m (23 ft) in length, with a weight of about 400 kg (880 lb), Dilophosaurus was one of the earliest large predatory dinosaurs and the largest known land-animal in North America at the time--though small compared to some of the later theropods. Its size was comparable to that of a brown bear.

A resting trace of a theropod similar to Dilophosaurus has been interpreted by some researchers as showing impressions of feathers around the belly and feet. Other researchers interpret these impressions as sedimentological artifacts created as the dinosaur moved, though this interpretation does not rule out that the track-maker could have borne feathers.

In the film adaptation, it is given the fictional ability to spit venom--a development that leads to the demise of disgruntled computer programmer Dennis Nedry. The real-life Dilophosaurus had no such ability.

Velociraptor and Dilophosaurus (two species responsible for fatalities in Jurassic Park) had top speeds of about 38 km per hour (24 mph), just below what a modern elephant can manage.

Dilophosaurus had 12 maxillary teeth and as many as 18 dentary teeth. The teeth were generally long and thin, with serrations on the front and back edges.

A 2007 study found that Dilophosaurus had features that indicate it may have eaten fish. The authors (Milner and Kirkland) point out that the ends of the jaws were expanded to the sides, forming a "rosette" of interlocking teeth, similar to those of spinosaurids, known to have eaten fish, and gharials, which includes the modern crocodile.