The fading sun beat down on our backs after an already long day in the field. Exhausted, we toiled over shovels and dug with our bare hands to clear away the sand. We were in the heart of dinosaur country on the Colorado Plateau of northern Arizona, working in the middle of the Navajo Nation to determine the ages of two skeletons of Dilophosaurus wetherilli that had been unearthed there previously. We had spent this hot June day in 2014 hiking up and down the badlands to measure the rock beds and fill our backpacks with geologic samples. And now we had to excavate—not a new dinosaur but rather our truck, which had gotten bogged down in the sand dunes and was buried up to the axles. The life of a globe-trotting field scientist is rooted in the mundane—applying for permits, taking notes, cooking meals and washing dishes in camp, reviewing the day's data by light of the campfire—rather than the swashbuckling of the movies. We never see Indiana Jones or Alan Grant digging out a stuck pickup truck.
In the summer of 1993 dinosaurs and paleontologists exploded onto movie screens around the world. Adapted from the 1990 Michael Crichton novel, Jurassic Park made instant stars, and villains, of several little-known species. Names such as Velociraptor and Dilophosaurus joined Tyrannosaurus and Triceratops in the public lexicon. The dinosaurs of action movies are typically not the animals that scientists know from nature. Yet one of the elements that made the Jurassic Park franchise so successful (it broke box office records in 1993 and topped the charts again in the summer of 2020) was its narrative reliance on the state of the art in paleontology and genetics. Author Crichton and director Steven Spielberg brought a modern look at dinosaur science to audiences for the first time, and the image they portrayed of active, intelligent animals still resonates today.
Of course, Crichton and Spielberg took artistic liberties to tell a compelling story, dramatizing not only the scientists but also the dinosaurs. The animal that departed most from the fossil evidence was Dilophosaurus. In the movie, it takes the form of a golden retriever–sized creature with a rattling frill and venomous spit that kills the computer programmer–turned–dinosaur embryo smuggler, Dennis Nedry. What was Dilophosaurus really like?
In truth, scientists did not have a complete picture of this animal back when it entered pop culture. But in the nearly three decades since Dilophosaurus got the Hollywood treatment, researchers have recovered significant new fossil specimens of this dinosaur and analyzed all of the remains with increasingly sophisticated methods. As a result, we can now reconstruct this dinosaur—its appearance and behavior, how it evolved, the world it inhabited—in detail. The findings show that the real Dilophosaurus bore little resemblance to its big-screen counterpart. They also provide the most detailed portrait yet of a dinosaur from the Early Jurassic epoch.
A Star is Born
Today we know Dilophosaurus as a bipedal, meat-eating dinosaur more than 20 feet long with two distinctive parallel crests of very thin bone along the top of its head (its name derives from the Greek words for “two-crested reptile”). But in 1954, when the animal first appeared in the scientific literature, it had a different name: in a series of papers, Samuel Welles, a University of California, Berkeley, paleontologist, presented his research on two skeletons found by Jesse Williams, a Navajo man who lived near Tuba City, Ariz. The crest had not been identified among the fragmentary remains, and Welles called the creature Megalosaurus wetherilli, believing it to be a new species in the previously known genus Megalosaurus. When Welles found an additional specimen in 1964 that preserved the top of the skull, with its dual crests, he realized that the original find represented a new genus, so he renamed the animal Dilophosaurus wetherilli.
The basic body plan of the dinosaur in Jurassic Park was patterned on Welles's 1984 anatomical description and sculpted reconstructions of the bones in museum exhibits, as well as artwork by paleontologist Gregory Paul in the 1988 book Predatory Dinosaurs of the World. But the Jurassic Park Dilophosaurus departed from the scientific record of the time in several key details. Most obviously, it was depicted as half the size of the real animal. The filmmakers did this deliberately to avoid any confusion with another saurian antagonist, the Velociraptor.
The hallmarks of the cinematic Dilophosaurus—namely, its venomous saliva and collapsible frill—were also fictional traits added for dramatic effect. But these embellishments resembled the biology of other real animals, which made them believable. When Welles described the fossils of Dilophosaurus, he interpreted some of the joints between the tooth-bearing bones at the end of the snout as “weak” and suggested that the animals may have been scavengers or that they did most of their killing with claws on their hands and feet. When writing the story, Crichton invented a dramatic mechanism by which the animals could spit a blinding venom, based on some modern species of cobras, which can spit two meters. Inspiration for the frill, meanwhile, came from the modern-day frilled agamid lizard that lives in Australia and New Guinea. The lizard has a structure made of bone and cartilage originating from the throat that supports the frill. No evidence of such a trait has turned up in the fossil record of Dilophosaurus.
Other aspects of Jurassic Park drew from the latest science. In the early 1980s paleontologists were just starting to reach broad agreement that modern birds descended from dinosaurs and are, in fact, the last surviving dinosaur lineage. The filmmakers threw out early test animations of sinuous, snakelike velociraptors in preference of recommendations from their science adviser, dinosaur paleontologist Jack Horner, to make the animals more birdlike in their movements. The film, with its depiction of dinosaurs as quick, clever animals rather than the sluggish, more lizardlike creatures that 19th-century scholars thought them to be, was the first time many members of the general public encountered the bird-dinosaur connection.
New and Improved
Artistic choices aside, scientific understanding of Dilophosaurus was bound to change in the years after Jurassic Park's release. In the lead-up to the book and film, the field of paleontology was undergoing tremendous change. Advances in computing were revolutionizing the study of fossils, enabling researchers to process enormous data sets in ways unimaginable when Dilophosaurus was first discovered. Take, for instance, cladistic analysis, which identifies discrete, heritable anatomical features that can be compared between animals and that provide a statistical basis for testing hypotheses about the relationships of animals to one another. Researchers can now analyze many more characteristics much more quickly than ever before and thus develop better-supported hypotheses about how dinosaurs are related and how they evolved. Increased computing power and developments in medical and industrial CT scanning also created a nondestructive way to look inside bones and rocks at hidden anatomy.
Not only did the analytical tools available to paleontologists evolve, but in 1998 teams at the University of Texas at Austin began recovering more Dilophosaurus remains in the same region of northern Arizona that yielded the first finds. Every new fossil discovery can support or refute prior thinking about long-vanished organisms. In this case, the new fossils preserved parts of the Dilophosaurus anatomy that were missing or distorted in previously collected specimens.
Fossils are typically collected in large blocks of rock and encased in plaster to protect them during their journey from the field to the laboratory. When they arrive in the museum, paleontologists use dental picks, chisels and miniature handheld jackhammers to carefully remove the rock and expose the fossils. After millions of years of exposure to geologic processes such as crushing and weathering, the fossils we find are most often distorted and incomplete elements. We sometimes disassemble and reconstruct broken fragments to better approximate their original condition, sculpting and adding missing material based on closely related animals.
When Wann Langston, Jr., and his colleagues prepared the first Dilophosaurus skeletons at U.C. Berkeley around 1950, they filled in missing skull parts with casts from the skull of a more complete carnivorous dinosaur from the Jurassic, and they sculpted missing parts of the pelvis out of plaster. No one really knew what those missing parts looked like; the reconstructions represented a hypothesis of the real form of Dilophosaurus—one that could be tested with new fossils.
The Dilophosaurus material discovered since Welles's initial description and Langston's reconstruction shows that the animal's snout and jaw were much more substantial than originally recognized. The upper jaw bones do not have the weak interface that the fragmentary first finds suggested. Instead these bones indicate a strong skull capable of biting into prey. Likewise, newly identified features of bones from the animal's lower jaw show stout ridges for muscle attachments. In modern reptiles, these ridges provide surface area for the attachment of large muscles. And the skeleton of a different dinosaur found at the U.T. Austin dig site—the plant-eating Sarahsaurus—features bite marks, attesting to the presence of a large meat-eating animal with jaws strong enough to puncture bone. Together this evidence supports the idea that Dilophosaurus was probably a predator with a deadly bite rather than a creature that had to scavenge or use its claws to kill, as Welles supposed.
Dilophosaurus was a large dinosaur, especially for its time. Most of the dinosaurs of the Late Triassic of western North America, just 20 million years earlier, were animals the size of turkeys or eagles, but Dilophosaurus would have towered over a human, standing up to eight feet tall and measuring up to 25 feet long when fully grown. It had much longer and stronger arms than other larger meat-eating dinosaurs such as Allosaurus and Ceratosaurus, and its legs were relatively longer as well. When the first skeletons of Dilophosaurus were found, scientists thought the species was related to the so-called carnosaurs Allosaurus and Streptospondylus, so they reconstructed the missing parts of the pelvis to look like they did in those animals. The better-preserved Dilophosaurus skeletons found later show more intermediate pelvis anatomy between Coelophysis-like and Allosaurus-like animals from the Late Triassic and Late Jurassic, respectively.
Like many early dinosaurs and all modern birds, Dilophosaurus had fleshy air pockets from its respiratory system growing into its vertebrae, which provided strength while simultaneously lightening the skeleton. These air sacs allowed for the unidirectional flow of air through the lungs—in other words, the entire cycle occurs in one breath, as it does in birds and crocodilians. This type of respiration provides the animal with more oxygen than does the bidirectional respiratory system that mammals have, in which air flows both in and out of the lungs. Animals that breathe unidirectionally tend to have relatively high rates of metabolism and thus high activity levels, so Dilophosaurus was probably a fast, agile hunter.
CT imaging has revealed that these air sacs are also present in the bones surrounding the dinosaur's brain and were continuous with the sinus cavities in the front of the skull. In most meat-eating dinosaurs, a ridge of bone provides a roof over an opening in the skull in front of the eye sockets known as the antorbital fenestra. But in Dilophosaurus, this opening is continuous with the side of the dinosaur's unique crests, suggesting that the crests, too, had air sacs. The crests were almost certainly covered by keratin, the same material that forms horns, claws and hair, and may have played a role in helping members of this species identify one another or attract mates. But how the air sacs might have supported these or other functions of the crests is unclear.
One of the challenges of studying the evolutionary history of any species is understanding physical variation within and among taxonomic groups. Welles thought the various skeletons we now categorize as Dilophosaurus actually represented multiple genera. Taking advantage of the latest cladistics tools, one of us (Marsh) tested that hypothesis by identifying hundreds of anatomical features present on each individual skeleton and comparing them with one another. The results of this statistical analysis show that, contrary to what Welles surmised, all of the animals are so similar that they must represent not only one genus but one species.
Marsh also incorporated these anatomical characteristics into a much larger data set that compares Dilophosaurus with other specimens from around the world. This process elucidates the early evolutionary history and biogeographical distribution of dinosaur groups and has more precisely located Dilophosaurus on the tree of life. We now know that the evolutionary gap between Dilophosaurus and its closest known relatives is significant, implying that many other, closer, relatives remain to be discovered.
Context Clues
Just as our conception of Dilophosaurus the animal has grown more detailed, so, too, has our understanding of the world it lived in. The hike down the Adeii Eichii Cliffs to the Dilophosaurus quarry is a journey back through 183 million years to the Early Jurassic. Back then, dinosaurs roamed the landscape, leaving footprints in what is now sandstone across the Colorado Plateau. Paved surfaces end miles from the rock outcrop, so we drive on overgrown rutted two-tracks that cross the loose sandy dune fields that show up on our geologic maps as “QAL”—Quaternary alluvium. This windblown sand is what stranded our field vehicles in 2014. The bedrock under these modern dunes is the Navajo Sandstone, the lithified remains of a 180-million-year-old desert. The red rock badlands of Ward Terrace, as this area is known, spill out to the western horizon, where they meet the much younger volcanic San Francisco Peaks of Flagstaff, Ariz. To the northwest is the mouth of one of the world's most visited geologic features, the Grand Canyon.
From the sands that trapped our pickup atop Ward Terrace to the Vishnu schist—the black rock at the bottom of the canyon that is being carved away by the Colorado River—these landscapes preserve much of the past 1.8 billion years of the rock record. As paleontologists, we work to understand the life entombed in those rocks, and we use lines of geologic and biological evidence preserved within them to reconstruct the environments of deep time.
One of our objectives was to more precisely determine the age of the rock in which Dilophosaurus is found, known as the Kayenta Formation. This rock was laid down by rivers, lakes and streams east of a volcanic arc that was depositing ash and fine-grained particles into the area. The ash helped to both preserve the bones of Dilophosaurus and aid early efforts to date the Kayenta Formation. We collected new rock samples to date using radiometric methods. We processed the samples by grinding and extracting zircon crystals, which can preserve unstable isotopes of uranium. The uranium isotope decays into lead at a constant rate, and when we vaporize the crystals with a laser and analyze them with a mass spectrometer, the relative quantities of uranium and lead we measure indicate when the rock layers were laid down. In the case of this Dilophosaurus site, it was around 183 million years ago, plus or minus a few million years.
Dilophosaurus thus lived during the Early Jurassic epoch, approximately five million to 15 million years after the end-Triassic mass extinction that resulted in the loss of roughly three quarters of life on Earth, including most of the large reptiles that competed for resources with the early dinosaurs. The mass extinction was probably triggered by the initial breakup of the supercontinent Pangaea as the northern Atlantic Ocean opened up like a volcanic zipper. Throughout the Late Triassic and Early Jurassic, the North American tectonic plate traveled northward from a subtropical climate belt into an arid climate belt, so the location that Dilophosaurus lived in moved from the approximate latitude of modern-day Costa Rica to modern-day northern Mexico. As such, the environment that deposited the Kayenta Formation was seasonally dry, with sand dunes migrating in and out of wetter environments where animals flourished.
Fossils of other organisms found in the Kayenta Formation reveal how Dilophosaurus fit into the ecosystem. It was the apex predator in the river oasis it inhabited, a conifer-lined waterway through a sea of sand. One specimen housed at U.T. Austin was found in the same quarry as two individuals of the long-necked herbivore Sarahsaurus. These dinosaurs lived alongside a smaller meat-eating dinosaur called Megapnosaurus and a small armored dinosaur called Scutellosaurus. The most common animal found in the Kayenta Formation is the early turtle Kayentachelys, which swam alongside heavily scaled bony fish, freshwater coelacanths and lungfish. Early mammal relatives, including the beaverlike tritylodontids and ratlike morganucodontids, were also potential prey for Dilophosaurus.
Fossils for All
In the fossil excavation depicted in Jurassic Park, a complete Velociraptor skeleton comes to light with some gentle brushing. In the real world, dinosaur fossils are typically found as broken, barely identifiable fragments. On a lucky day, a mostly complete bone might turn up. With the publication last summer of Marsh's comprehensive anatomical study, Dilophosaurus has become the best-documented Early Jurassic dinosaur from anywhere in the world. But it took decades to find additional remains that filled in the unknown anatomy of the animal. And it took successive generations of paleontologists to interpret the bones.
Museums play a vital role in facilitating such efforts. The public's conception of museums is a dramatically lit exhibit gallery, but the major function of a natural history museum is to conduct research into the natural world. To that end, these institutions build large collections of specimens to serve as the evidence for scientific research. Teams of specially trained conservators, archivists and collection managers carefully document and preserve the specimens, with the goal of making the collections accessible to researchers in perpetuity. Repeatability is a cornerstone principle of scientific research; other scientists must be able to corroborate our findings. In paleontology, that means that the fossils themselves must be preserved in a museum, so that future generations of scientists can revisit the specimens and double-check observations.
The Navajo Nation has partnered with museums that care for those fossils to preserve not just the bones themselves but all the archives and data associated with them. In 2015, when we went to relocate the original Dilophosaurus discovery site for this research, we were lucky to meet John Willie, a relative of Jesse Williams, the Navajo man who found the first bones in 1940. Willie walked us to the site and explained that the natural resources unique to the Navajo Nation are extremely important to the Diné (Navajo People). The Navajo Nation is one of the best places in the world to see terrestrial rocks from the Early Mesozoic era, and its Minerals Department has been active in facilitating scientific research, including approving permits for fieldwork and loans of fossils and reviewing scientific manuscripts.
Scientific understanding comes from building on and reevaluating prior knowledge and sometimes overturning old notions. It is exciting when this hard-won information filters into pop culture. Paleontology has close ties with cinema going to the dawn of animation. Winsor McCay's 1914 Gertie the Dinosaur opens with the animator and a group of friends visiting the American Museum of Natural History in New York City, looking at the skeleton of a sauropod dinosaur. McCay bets his party that he can bring the animal to life; the result is the first dinosaur to appear on film. McCay consulted with paleontologists at the museum for guidance on his reconstruction of Gertie. Later Barnum Brown, the discoverer of Tyrannosaurus rex, provided expertise to Walt Disney during the production of its 1940 animated film Fantasia. And the studio behind the 1954 Godzilla found inspiration for the design of its monster in the dinosaurs that appeared in a 1947 mural by Rudolph Zallinger entitled The Age of Reptiles, housed at the Yale Peabody Museum. With the Jurassic Park film franchise set to release its sixth installment in 2022, we look forward to seeing how paleontology is represented.
Incidentally, the reverse is also true. Pop culture filters into science, sometimes literally. Langston once recounted that while repairing fossils at U.C. Berkeley in the 1930s and 1940s, the paleontologists would dissolve cellulose acetate film strips in acetone to make glue rather than buy the more expensive Duco Cement. So, yes, Dilophosaurus is in the movies. But perhaps there is a little bit of the movies in Dilophosaurus, too.
AUTHORS' NOTE: Fieldwork on the Navajo Nation was conducted under a permit from the Navajo Nation Minerals Department. Any persons wishing to conduct geologic investigations on the Navajo Nation must first apply for and receive a permit from the Navajo Nation Minerals Department, P.O. Box 1910, Window Rock, Arizona 86515, and telephone no.: (928) 871-6587.
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