Dilophosaurus

*Dilophosaurus wetherilli*

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***Dilophosaurus*** was one of the largest carnivorous dinosaurs of the Early Jurassic Period. *Dilophosaurus* gets its name from the two thin crests of bone on the top of its head. These were probably used as a display for courtship purposes. (Its frill and ability to spit venom at its prey is actually made up and there is no proof if it had such abilities) *Dilophosaurus* has been found in Northern Arizona.

As a more primitive predatory dinosaur, *Dilophosaurus* didn't have forward facing eyes to give it stereo vision. It may have used scent as an integral part of its hunting technique. It had long and slender, rear-curving teeth in long jaws and strong front arms which would have been effective in grabbing prey. It was fast - probably with a top speed of about 30-mph. Footprints attributed to *Dilophosaurus* appear in groups, so it may have hunted in small packs. It shares the same overall body configuration as *Coelophysis* even though *Dilophosaurus* is currently classified as a member of a different group of theropods rather than *Coelophysis* and its relatives.

## History of discovery

In the summer of 1942, the American paleontologist Charles L. Camp led a field party from the University of California Museum of Paleontology (UCMP) in search of fossil vertebrates in Navajo County in northern Arizona. Word of this was spread among the Native Americans there, and the Navajo Jesse Williams brought three members of the expedition to some fossil bones he had discovered in 1940. The area was part of the Kayenta Formation, about 32 kilometers (20 mi) north of Cameron near Tuba City in the Navajo Indian Reservation. Three dinosaur skeletons were found in purplish shale, arranged in a triangle, about 9.1 meters (30 ft) long at one side.

The first was nearly complete, lacking only the front of the skull, parts of the pelvis, and some vertebrae. The second was very eroded, included the front of the skull, lower jaws, some vertebrae, limb bones, and an articulated hand. The third was so eroded that it consisted only of vertebra fragments. The first good skeleton was encased in a block of plaster after ten days of work and loaded onto a truck, the second skeleton was easily collected as it was almost entirely weathered out of the ground, but the third skeleton was almost gone.

## Description

*Dilophosaurus* measured around 6 metres (20 ft) long and may have weighed half a ton. Fossils of the animal have been found at the Navajo Indian Reservation, just west of Tuba City, Arizona, USA and in the Kayenta Formation. Just a few tens of feet below the level of the bones, large footprints of carnivorous dinosaurs were found and these may belong to *Dilophosaurus*. It lived in the Early Jurassic Period, from the Sinemurian to the Pliensbachian stages (193-183 million years ago), and was more primitive than later carnivores of the Jurassic, such as *Ceratosaurus* or *Allosaurus*.

The original description was published in 1954, by the renowned paleontologist Samuel Welles. However, at the time, it was thought to be another genus of theropod (*Megalosaurus*). In 1970, it was recognized to be distinct and given its own generic name *Dilophosaurus*. Welles later redescribed the entire taxon in 1984, in a more comprehensive paper. *Dilophosaurus* may be a primitive member of the clade containing both ceratosaurian and tetanuran theropods. Alternatively, some paleontologists classify this genus as a large coelophysoid. Recent *Dilophosaurus* 'skin imprints', associated with a set of footprints, seemed to suggest that it had feathers but further study revealed these to be impressions of plant material.

Footprints of a *Dilophosaurus-*like predator have been discovered in the Lavini di Marco area, near Rovereto (Trentino, northern Italy).

Meanehile the Dilophosaurus true diet is unknown; it is assumed that the animal had probably a mixed diet of both terrestrial and aquatic prey; similiar to spinosaurids, as its speculated to be large enough to hunt large prosauropods as well as smaller dinosaurs including the local species of coelophysis (*C. kayentakae*) and *Sarahsaurus*. Latest research also concluded the possiblity of fish-hunting on rivers and delta's.

## Classification

In 1954 Welles thought that *Dilophosaurus* was a megalosaur, but later in 1970 revised his opinion because he discovered *Dilophosaurus* had crests. By 1974 Welles and paleontologist Robert A. Long found Dilophosaurus to be a ceratosauroid, and in 1984 he found that *Dilophosaurus* exhibited features of both Coelurosauria and Carnosauria, the two main groups into which theropods had hitherto been divided, based only on body size, and he suggested this division was inaccurate. Welles found *Dilophosaurus* to be closest to the theropods that were placed in Halticosauridae, especially *Liliensternus*.

In 1988 Gregory Paul classified halticosaurs as a subfamily of the family Coelophysidae, and proposed that *Dilophosaurus* could have been a direct descendant of *Coelophysis*. He also considered the possibility that spinosaurs were late-surviving dilophosaurs, based off the similar nostril position, kinked snouts, and slender teeth of *Baryonyx*. In the year 1994, paleontologist Thomas R. Holtz placed *Dilophosaurus* in the Superfamily Coelophysoidea, along with but separate from the Coelophysidae. Thomas Holtz placed Coelophysoidea in Ceratosauria, and in 2000, paleontologist James H. Madsen and Welles divided Ceratosauria into the families Ceratosauridae and Dilophosauridae.

In 1998 Lamanna and colleagues pointed out that since *Dilophosaurus* was discovered to have had crests on its skull, other similarly crested theropods have been discovered (including *Sinosaurus*), and that this feature is, thus, not unique to the genus, and of limited use for determining interrelationships within the group. Paleontologist Adam M. Yates described the genus *Dracovenator* from South Africa in 2005, finding it closely related to *Dilophosaurus* and *Zupaysaurus*. His cladistic analysis suggested they did not belong in the Coelophysoidea, but instead in Neotheropoda, a more derived (or '"advanced"') group.

He suggested that if *Dilophosaurus* was more derived than the Coelophysoidea, the features it had with this grouping may have been inherited from basal (or '"primitive"') theropods, indicating that theropods may have passed through a "coelophysoid stage" in their early evolution.

In the year 2007, Nathan D. Smith and colleagues found the crested theropod *Cryolophosaurus* to be a sister species of *Dilophosaurus*, and grouped them with *Dracovenator* and *Sinosaurus*. This clade was more derived than the Coelophysoidea, but more basal than the Ceratosauria, as a result of that placing basal theropods in a ladder-like arrangement. In 2012, paleontologist Carrano and colleagues found that the group of crested theropods proposed by Smith and colleagues was based on features that relate to the presence of such crests, but that the features of the rest of the skeleton were less consistent. They instead found that *Dilophosaurus* was a coelophysoid, with *Cryolophosaurus* and *Sinosaurus* being more derived, as basal members of the group Tetanurae.

The paleontologist Christophe Hendrickx, and colleagues defined the Dilophosauridae to include *Dilophosaurus* and *Dracovenator* in 2015, noting that while general uncertainty exists about the placement of this group, it appears to be slightly more derived than the Coelophysoidea, and the sister group to the Averostra. Dilophosauridae share features with the Coelophysoidea such as the subnarial gap and the front teeth of the maxilla pointing forwards, whilst features shared with Averostra include a fenestra at the front of the maxilla and a reduced number of teeth in the maxilla, they suggested that the cranial crests of *Cryolophosaurus* and *Sinosaurus* had either evolved convergently, or were a feature inherited from a common ancestor.

In 2019, Marion Zahner and Winand Brinkmann found the members of the Dilophosauridae to be a successive basal sister taxa of the Averostra rather than a monophyletic clade (a natural group), but noted that some of their analyses did find the group valid, containing *Dilophosaurus*, *Dracovenator*, *Cryolophosaurus*, and possibly *Notatesseraeraptor* as the basal-most member. They then provided a diagnosis for Dilophosauridae, based on features in the lower jaw. In the phylogenetic analysis accompanying their 2020 redescription, Rower and Marsh found all specimens of *Dilophosaurus* to form a monophyletic group, sister to Averostra, and to be more derived than *Cryolophosaurus*. Their analysis did not find support for Dilophosauridae, and then suggested cranial crests were a plesiomorphic (ancestral) trait of Ceratosauria and Tetanurae.

## Ichnology

Multiple ichnotaxa (taxa based on trace fossils) have been assigned to *Dilophosaurus* or other similar theropods. Welles in 1971, reported dinosaur footprints from the Kayenta Formation of northern Arizona on two levels 14 m (45 ft) and 112 m (367 ft) below where the original *Dilophosaurus* specimens were found.

## Skull and Crests

The most distinctive characteristic of *Dilophosaurus* was the pair of rounded crests on its skull, probably used for display. Studies by Rob Gay (2001) show that these crests may have been larger in one sex than in the other. Another curious skull feature was a notch behind the first row of teeth, giving it an almost crocodile-like appearance. This "notch" existed by virtue of a weak connection between the premaxillary and maxillary bones of the skull. This conformation led to the early hypothesis that *Dilophosaurus* scavenged off dead carcasses, with the front teeth being too weak to bring down and hold large prey. A similar notch is present in most other species of coelophysoid.

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## Species

There is another species of *Dilophosaurus* (*D. sinensis*), which may or may not belong to this genus. It is possibly closer to the bizarre Antarctic theropod *Cryolophosaurus*, based on the fact that the anterior end of the jugal does not participate in the internal antorbital fenestra and that the maxillary tooth row is completely in front of the orbit and ends anterior to the vertical strut of the lacrimal. This species was recovered from the Yunnan Province of China in 1987, with the prosauropod *Yunnanosaurus* and later described and named in 1993 by Shaojin Hu.

## JPInstitute.com Description

Dilophosaurus was the largest meat-eater of the early Jurassic. It was made famous by the movie Jurassic Park, but the movie did not present an accurate picture of this dinosaur. Because it was the biggest and most ferocious of its time, it would not have needed to be poisonous (it was probably not a "spitter" like in the movie). It is also much larger than the movie version.

Dilophosaurus gets its name from the two thin crests of bone on the top of its head. These were probably used as a display for courtship purposes (scientists don't believe it had a frill on its neck like the movie version). Dilophosaurus has been found in both the U.S. and China, which, although part of the same huge landmass, were still quite a long distance from each other.

As an early predatory dinosaur, Dilophosaurus did not have forward facing eyes to give it stereo vision. It may have used scent as an integral part of its hunting technique. It had long and slender, rear-curving teeth in long jaws and strong front arms which would have been effective in grabbing prey. It was fast - probably with a top speed of about 30-mph. It also had a long tail that could have been used as a whip in a fight. Footprints attributed to Dilophosaurus appear in groups, so it may have hunted in small packs. It shares the same overall body configuration as its ancestor the Coelophysis.

## Dinosaur Field Guide Description

Dilophosaurus ("double-crested lizard") was one of the first large meat-eating dinosaurs. It was a close relative of the smaller dinosaur Coelophysis. Little Coelophysis lived in the Late Triassic, when Rauisuchus and other reptiles related to the ancestors of crocodilians were the top predators. At the end of the Triassic, however, there was a series of great extinctions, and the giant crocodile relatives became extinct. Dinosaurs then became the top meat-eaters. In general, Dilophosaurus looks like a shorter-necked, more heavily built version of Coelophysis. Like its little relative, Dilophosaurus has a characteristic "kink" in the front of its snout. This probably helped hold on to struggling victims. One dramatic difference (other than
size) between the two is the pair of tall crescent-shaped crests along the top of Dilophosaurus's skull. These were very thin and probably used only for display. Footprints that match the feet of Dilophosaurus are found in many parts of the world, dating from Early Jurassic. Since the continents of the Earth were still mostly attached as the supercontinent of Pangaea at this time (see map on page 151), it is possible that the double-crested hunter lived in most parts of the world.

### Fun Facts

The state fossil of Connecticut is a dinosaur footprint, very likely the footprint of Dilophosaurus or a close relative.

### Trivia

When the first skeleton of this dinosaur was found (in 1942), it was thought to be from a new species of Megalosaurus. Only later in the lab did paleontologist Sam Welles discover the pair of crests on its head.

## Links

http://web.archive.org/web/20031219053925fw\_/http://www.jpinstitute.com/dinopedia/dinocards/dc\_dilop.html#

## References

1. ↑ Dinopedia on the JPI site
2. ↑ http://files.geology.utah.gov/surveynotes/articles/pdf/fishing\_dinos\_39-3.pdf