Dilophosaurus
Dilophosaurus is a genus of theropod dinosaurs that lived in what is now North America during the Early Jurassic, about 186 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, an explorer and amateur archeologist. Further specimens have since been found, including an infant. Fossil 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 in length, with a weight of about, Dilophosaurus was one of the earliest large predatory dinosaurs and the largest known land-animal in North America at the time. 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, arched crests on its skull; their complete shape is unknown, but they were probably enlarged by keratin. 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; the fourth was vestigial. The thigh bone was massive, the feet were stout, and the toes bore large claws.
Dilophosaurus has been considered a member of the family Dilophosauridae along with Dracovenator, a group placed between the Coelophysidae and later theropods, but some researchers have not found support for this grouping. 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 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 Scutellosaurus and Sarahsaurus. It was designated as the state dinosaur of Connecticut based on tracks found there. Dilophosaurus was featured in the novel Jurassic Park and its movie adaptation, where it was given the fictional abilities to spit venom and expand a neck frill, and was depicted as smaller than the real animal.
History of discovery
In the summer of 1942, the paleontologist Charles L. Camp led a field party from the University of California Museum of Paleontology 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 north of Cameron near Tuba City in the Navajo Indian Reservation. Three dinosaur skeletons were found in purplish shale, arranged in a triangle, about 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 vertebral fragments. The first good skeleton was encased in a block of plaster after 10 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.The nearly complete first specimen was cleaned and mounted at the UCMP under supervision of the paleontologist Wann Langston, a process that took three men two years. The skeleton was wall-mounted in bas relief, with the tail curved upwards, the neck straightened, and the left leg moved up for visibility, but the rest of the skeleton was kept in its burial position. As the skull was crushed, it was reconstructed based on the back of the skull of the first specimen and the front of the second. The pelvis was reconstructed after that of Allosaurus, and the feet were also reconstructed. At the time, it was one of the best-preserved skeletons of a theropod dinosaur, though incomplete. In 1954, the paleontologist Samuel P. Welles, who was part of the group who excavated the skeletons, preliminarily described and named this dinosaur as a new species in the existing genus Megalosaurus, M. wetherilli. The nearly complete specimen was made the holotype of the species, and the second specimen was made the paratype. The specific name honored John Wetherill, a Navajo councilor whom Welles described as an "explorer, friend of scientists, and trusted trader". Wetherill's nephew, Milton, had first informed the expedition of the fossils. Welles placed the new species in Megalosaurus due to the similar limb proportions of it and M. bucklandii, and because he did not find great differences between them. At the time, Megalosaurus was used as a "wastebasket taxon", wherein many species of theropods were placed, regardless of their age or locality.
Welles returned to Tuba City in 1964 to determine the age of the Kayenta Formation, and discovered another skeleton about south of where the 1942 specimens had been found. The nearly complete specimen was collected with the help of William J. Breed of the Museum of Northern Arizona and others. During preparation of this specimen, it became clear that it was a larger individual of M. wetherilli, and that it would have had two crests on the top of its skull. Being a thin plate of bone, one crest was originally thought to be part of the missing left side of the skull, which may had been pulled out of its position by a scavenger. When it became apparent that it was a crest, it was also realized that a corresponding crest would have been on the left side, since the right crest was right of the midline, and was concave along its middle length. This discovery led to re-examination of the holotype specimen, which was found to have bases of two thin, upwards-extended bones, which were crushed together. These also represented crests, but they had formerly been assumed to be part of a misplaced cheek bone. The two 1942 specimens were also found to be juveniles, while the 1964 specimen was an adult, about one-third larger than the others. Welles later recalled that he thought the crests were as unexpected as finding "wings on a worm".
New genus and subsequent discoveries
Welles and an assistant subsequently corrected the wall mount of the holotype specimen based on the new skeleton, by restoring the crests, redoing the pelvis, making the neck ribs longer, and placing them closer together. After studying the skeletons of North American and European theropods, Welles realized that the dinosaur did not belong to Megalosaurus, and needed a new genus name. At that time, no other theropods with large longitudinal crests on their heads were known, and the dinosaur had therefore gained the interest of paleontologists. A mold of the holotype specimen was made, and fiberglass casts of it were distributed to various exhibits; to make labeling these casts easier, Welles decided to name the new genus in a brief note, rather than wait until the publication of a detailed description. In 1970, Welles coined the new genus name Dilophosaurus, from the Greek words di meaning "two", lophos meaning "crest", and sauros meaning "lizard": "two-crested lizard". Welles published a detailed osteological description of Dilophosaurus in 1984, but did not include the 1964 specimen, since he thought it belonged to a different genus. Dilophosaurus was the first well-known theropod from the Early Jurassic, and remains one of the best-preserved examples of that age.In 2001, the paleontologist Robert J. Gay identified the remains of at least three new Dilophosaurus specimens in the collections of the Museum of Northern Arizona. The specimens were found in 1978 in the Rock Head Quadrangle, away from where the original specimens were found, and had been labeled as a "large theropod". Though most of the material is damaged, it is significant in including elements not preserved in the earlier specimens, including part of the pelvis and several ribs. Some elements in the collection belonged to an infant specimen, the youngest known example of this genus, and one of the earliest known infant theropods from North America, only preceded by some Coelophysis specimens. The juvenile specimen includes a partial humerus, a partial fibula, and a tooth fragment. In 2005, paleontologist Ronald S. Tykoski assigned a specimen from Gold Spring, Arizona, to Dilophosaurus, but in 2012, paleontologist Matthew T. Carrano and colleagues found it to differ in some details.
In 2020, the paleontologists Adam D. Marsh and Timothy B. Rowe comprehensively redescribed Dilophosaurus based on the by then known specimens, including specimen UCMP 77270 which had remained undescribed since 1964. They also removed some previously assigned specimens, finding them too fragmentary to identify, and relocated the type quarry with the help of a relative of Jesse Williams. In an interview, Marsh called Dilophosaurus the "best worst-known dinosaur", since the animal was poorly understood despite having been discovered 80 years earlier. A major problem was that previous studies of the specimens did not make clear which parts were original fossils and which were reconstructed in plaster, yet subsequent researchers only had Welles' 1984 monograph to rely on for subsequent studies, muddling understanding of the dinosaur's anatomy. Marsh spent seven years studying the specimens to clarify the issues surrounding the dinosaur, including two specimens found two decades earlier by Rowe, his Ph.D. advisor.