This photo shows a scene from a 1942 excavation by UC Berkeley scientists, when a
Dilophosaurus specimen was discovered.
University of California Museum of Paleontology
Now, the new analysis includes two previously unstudied fossil specimens from Arizona, providing the first clear picture of what
Dilophosaurus was like in life. Rather than a small dinosaur that relied on gimmicks such as venom and a neck frill to subdue its prey , Dilophosaurus was a powerful predator and one of the largest land animals in North America when it lived during the early Jurassic period, which lasted from about 201 to 174 million years ago.
“It’s a lot bigger than people would think from watching Jurassic Park,” Marsh says.
Part fossil, part plaster
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 at the University of California, Berkeley, including Samuel Welles, who named it as a new species in 1954.
The team that reconstructed the dinosaur for display used plaster versions of bones to fill in for missing fossils. The resulting dinosaur was “intentionally made to look like [the different predator]
Allosaurus … because it was going on a wall mount and they wanted to make it look complete,” Marsh says. The trouble is that the 1954 study, and additional research that Welles published in 1984, didn’t make clear which bones were actual fossils and which were plaster parts.
Subsequent research based on these early papers led to confusion about whether
Dilophosaurus was more closely related to turkey-size Triassic carnivores, such as Coelophysis, or larger late Jurassic species, such as Ceratosaurus and Allosaurus.
“It just wasn’t clear after 1984 if they were talking about real anatomy or something described from plaster,” Marsh says. Without anyone spending time and resources on further study, the muddled picture of the animal’s anatomy persisted for decades.
Over a thousand dinosaur species once roamed the Earth. Learn which ones were the largest and the smallest, what dinosaurs ate and how they behaved, as well as surprising facts about their extinction.
“Everyone has relied on that one monograph for their research purposes in one way or another, but it turns out there were some problems with how that paper was put together,” says
Peter Makovicky, a paleontologist at the University of Minnesota who was not involved in the new study.
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To set the record straight, Marsh spent seven years studying each of the three most complete
Dilophosaurus skeletons, which are owned by the Navajo Nation and housed at UC Berkeley. He also examined two unstudied specimens found on Navajo land two decades ago by University of Texas at Austin paleontologist Timothy Rowe, a coauthor of the new research who was Marsh’s Ph.D. advisor.
The early research on
Dilophosaurus suggested it had weak jaws and a fragile crest—something Marsh believes may have influenced the depiction of the animal as a slender dinosaur that spat venom in Michael Crichton’s 1990 novel Jurassic Park.Neither the venom nor the neck frill that was added in the movie have any basis in fossil evidence.
The new fossils include a complete hind leg and several parts of the skeleton not known from the earlier specimens, including the braincase and the pelvis, and the bones show that
Dilophosaurus had strong jaws equipped with powerful muscles. It was 20 feet long—about half the size of a full-grown T. rex—and it weighed three-quarters of a ton, meaning it would have easily taken large prey that lived alongside it in the same environments, such as Sarahsaurus, an SUV-size relative of long-necked sauropods.
Wann Langston, Jr., at UC, Berkeley, supervises the reconstruction of the first skeleton of
Dilophosaurus in the early 1950s.
Texas Vertebrate Paleontology Collections
Dilophosaurus is clearly built for being a big macropredator,” Marsh says. “It’s a large-bodied animal that was built for eating other animals.”
The work is a “very welcome description of this animal,” says
Martín Ezcurra, a paleontologist who studies early meat-eating dinosaurs at the Bernardino Rivadavia Natural Sciences Argentine Museum in Buenos Aires. “It’s very interesting that the authors have increased the number of specimens … telling us that Dilophosaurus was more common in early Jurassic ecosystems than we thought.”
One feature shown in
Jurassic Park that was accurate is the double crest that runs along the top of the creature’s snout. Likely a display feature, the crest may have been brightly colored in life, and it could have been used to intimidate rivals or woo mates, similar to a deer’s antlers or a peacock’s tail.
“It’s such a stunning animal. It has those two thin bony crests running along the top of its skull, basically from the nostril and back over the eye socket,” Makovicky says.
Despite being built of thin bone, this crest, which is “unique in its construction,” was reinforced with a honeycomb of air pockets to strengthen and protect it, Marsh says. He and Rowe also found that air pockets continue through the braincase and other bones of the skeleton, hinting at how
Dilophosaurus’ ancestors developed lighter skeletons. This allowed the animals to attain greater sizes without being crippled by their own weight, becoming North America’s first large meat-eating dinosaurs.
The spaces in the crest—which join up with the animal’s nasal passages—may have even been attached to inflatable air sacs for display, potentially of the type seen in
modern frigate birds. However, the theory will have to be tested by other paleontologists using the newly published anatomical data, Marsh says.
Dilophosaurus, Cryolophosaurus, and related crested dinosaurs from China and Argentina all appear in the early Jurassic, representing “a sudden increase in body size across the Triassic-Jurassic boundary, thought to coincide with the disappearance of large crocodile-line [predators],” Makovicky says. “That top predator niche is up for grabs, and these crested dinosaurs seem to jump into it very quickly.”
Despite their initial success, the crested dinosaurs were only around for a short time in evolutionary terms—a few tens of millions of years—before they were replaced by species such as
Ceratosaurus and Allosaurus. Head crests are much less common in later dinosaurs, perhaps because these animals began to develop feathers, which would have been more effective displays and less biologically expensive than sheets of bone.
“In many ways,
Dilophosaurus is a keystone species for our understanding of theropods in the early Jurassic,” Makovicky says. “But the literature on it has been outdated for a very long time.”