Dilophosaurus was a formidable predator, stretching roughly 6 to 7 meters (about 20 to 23 feet) from snout to tail tip and standing around 1.5 meters (close to 5 feet) at the hip. Weight estimates generally fall in the range of 300 to 400 kilograms, or roughly 660 to 880 pounds. That makes it far larger than the dog-sized creature depicted in the 1993 film that introduced it to popular culture, and a landmark in the definitive 2020 scientific monograph on the species confirmed its status as the largest land animal known from Early Jurassic North America.
What the Fossil Record Actually Tells Us
Dilophosaurus wetherilli was first described in 1954 from specimens collected in the Kayenta Formation of northern Arizona, rocks dating to roughly 193 million years ago. For decades, the scientific picture of the animal relied on a relatively small number of fossils, some of which were incomplete or poorly preserved. That changed dramatically with a comprehensive 2020 study that redescribed the original holotype alongside referred specimens and previously undescribed material. That work established that all the crested theropod material from the Kayenta Formation belongs to a single species, eliminating earlier confusion about whether there might be more than one kind of large, crested predator roaming that landscape.1Journal of Paleontology. A comprehensive anatomical and phylogenetic evaluation of Dilophosaurus wetherilli (Dinosauria, Theropoda) with descriptions of new specimens from the Kayenta Formation of northern Arizona
Individual specimens vary in size, which is expected given that they represent animals at different stages of growth. Some are noticeably smaller than others, suggesting subadults. But even the smaller individuals were sizeable animals, and the largest specimens are consistent with the 6-to-7-meter length range. The variation among known fossils also means that published weight estimates can differ depending on which specimen a researcher uses as the basis for calculation and which method they apply.
Why Weight Estimates Span a Range
Pinning down exact body mass for an extinct animal is inherently uncertain. Paleontologists use several approaches, and each has limitations. One common method involves measuring the circumference of the femur (thighbone) and applying scaling equations derived from living animals. Another builds three-dimensional body models around the skeleton and calculates volume, then converts that volume to mass using assumptions about tissue density. Recent work using digital 3D scans of physical models, scaled to published body-size estimates, has been applied to Dilophosaurus alongside other theropods ranging from the small Coelophysis to the massive Tyrannosaurus.2Journal of Iberian Geology. Digital 3D models of theropods for approaching body-mass distribution and volume
The spread of 300 to 400 kilograms you commonly see for Dilophosaurus reflects this methodological variety. Some older estimates ran a bit lower, and some volumetric reconstructions have pushed the upper end higher. The 2020 monograph’s detailed anatomical work gives modelers better skeletal proportions to work from than were previously available, which has helped narrow the range. Still, any single number you see quoted for Dilophosaurus body mass should be treated as an informed estimate rather than a measurement.
The Largest Land Animal of Its Time and Place
Dilophosaurus holds a distinction that helps put its size in perspective: it was the biggest animal walking on land in North America during the Early Jurassic.1Journal of Paleontology. A comprehensive anatomical and phylogenetic evaluation of Dilophosaurus wetherilli (Dinosauria, Theropoda) with descriptions of new specimens from the Kayenta Formation of northern Arizona That might sound unremarkable until you consider the context. Early Jurassic ecosystems were still recovering from the end-Triassic extinction, which had cleared away many of the large reptile lineages that dominated the Late Triassic. Dilophosaurus represented one of the first theropod dinosaurs to reach what we would consider truly large body size. Most Late Triassic theropods were considerably smaller, and Dilophosaurus shows anatomical changes in its spine and skeleton that researchers have associated with both an increase in body size and a shift toward active predation of large prey.1Journal of Paleontology. A comprehensive anatomical and phylogenetic evaluation of Dilophosaurus wetherilli (Dinosauria, Theropoda) with descriptions of new specimens from the Kayenta Formation of northern Arizona
To be clear, Dilophosaurus was nowhere near the size of the giant theropods that came tens of millions of years later. An Allosaurus from the Late Jurassic could reach 9 meters or more, and Tyrannosaurus rex, which lived roughly 125 million years after Dilophosaurus, weighed perhaps 8,000 kilograms. Dilophosaurus was a fraction of that mass. But in its own world, it was the apex, the largest predator and the largest terrestrial animal in its ecosystem. That ecological position matters more than raw numbers when you are trying to understand what kind of animal it was.
Anatomy Built for a Large Predator
Several features of Dilophosaurus anatomy reflect adaptations to its size. The vertebral column shows what researchers describe as “shoulders” projecting from the front and back faces of the neural spines, the bony projections that rise from the top of each vertebra. These structures appear to be part of the bone itself rather than ossified ligaments, and they likely served as attachment points for the muscles and connective tissues needed to support a large body during movement.3PLOS ONE. Vertebral Adaptations to Large Body Size in Theropod Dinosaurs
Another relevant feature is skeletal pneumaticity, the presence of air-filled spaces within certain bones. This trait is well documented in theropod dinosaurs and shows up in Dilophosaurus. Research across Theropoda has found that evolutionary increases in pneumaticity tend to be concentrated in lineages with large body size, suggesting that reducing skeletal weight helped offset the gravitational costs of being big.4PubMed Central. Air-filled postcranial bones in theropod dinosaurs: physiological implications and the ‘reptile’-bird transition In practical terms, Dilophosaurus may have been somewhat lighter for its body length than you would expect if its bones were solid throughout. This is one reason volumetric mass estimates can be tricky: the density assumptions you plug in affect the final number, and pneumatic bones shift the equation.
The skull was large relative to the body, with a long snout and relatively tall maxillae (upper jaw bones). The jaws carried rows of curved, blade-like teeth suited to gripping and tearing flesh. Phylogenetically, Dilophosaurus sits outside the group that includes most later large theropods. It is not a ceratosaur or a coelophysoid, as some earlier studies proposed, but rather a non-averostran neotheropod on the stem leading to the more derived theropod groups.1Journal of Paleontology. A comprehensive anatomical and phylogenetic evaluation of Dilophosaurus wetherilli (Dinosauria, Theropoda) with descriptions of new specimens from the Kayenta Formation of northern Arizona In plain terms, it was an early branch of the theropod family tree, not a close relative of the famous later giants. Its large size was evolved independently from theirs.
Those Distinctive Double Crests
The feature that gives Dilophosaurus its name (which translates to “two-crested lizard”) is the pair of parallel bony crests running along the top of the skull. These are thin, fragile-looking structures made of extensions of the nasal and lacrimal bones. They were almost certainly display features, used in species recognition or mate selection, much like the head crests of modern cassowaries or hornbills.
A question that comes up often is whether the crests affected how Dilophosaurus could use its jaws. Recent biomechanical analysis of feeding mechanics in large theropods found that cranial ornamentation like crests and horns, including those of Dilophosaurus, had limited impact on feeding performance. Stress values in ornamented skulls were comparable to those of similarly sized theropods without such features.5Current Biology. Gigantism and feeding mechanics in large theropod dinosaurs The crests were not making the skull weaker or limiting what it could bite. They were essentially add-ons that did not compromise the animal’s ability to function as a predator.
The crests were also far too thin and delicate to have been used as weapons. They were not battering rams or slashing instruments. Their value was visual, and their fragility is one reason they are not always well preserved in fossils, which historically contributed to confusion about exactly what Dilophosaurus looked like.
Footprints That Match the Body
Dilophosaurus left more than bones behind. Large, three-toed footprints from Early Jurassic formations in the eastern United States and elsewhere, classified under the ichnogenus Eubrontes, have long been attributed to large theropod dinosaurs. Dilophosaurus is one of the most commonly cited trackmakers for these prints, given that its foot proportions and estimated body size are a good match. Some researchers have debated whether early sauropodomorphs might have produced some Eubrontes tracks, but most paleontologists continue to identify theropods as the primary makers.6BioOne Complete. Pedal Skeletal Proportions of Bipedal and Potentially Bipedal Dinosaurs and Other Archosaurs: Interpreting the Makers of Early Mesozoic Footprints
Eubrontes tracks can measure 30 centimeters or more in length, which is consistent with an animal in the 6-to-7-meter body-length range. Tracks also provide information that bones alone cannot: stride length, gait, speed estimates, and whether the animal was walking or running. These trace fossils reinforce the picture of Dilophosaurus as a large, active bipedal predator that covered ground efficiently.
Evidence of a Tough Life
One Dilophosaurus specimen offers a vivid window into what life was like at this body size. The individual had eight afflicted bones in its pectoral girdle and forelimb. On its left side, it had a fractured shoulder blade and radius along with large abscesses in the ulna and the base of its thumb. On its right side, there was abnormal torsion of the upper arm bone, bony tumors on the radius, a truncated joint surface on one of the hand bones, and angular deformities in a finger. Despite all of this damage, the bone showed extensive healing and remodeling, meaning the animal survived for months and possibly years after these problems began.7PubMed Central. Record-Breaking Pain: The Largest Number and Variety of Forelimb Bone Maladies in a Theropod Dinosaur
Some of these deformities may have resulted from developmental osteodysplasia, a condition known in modern birds but previously unreported in non-avian dinosaurs. The fact that this Dilophosaurus could survive such extensive injuries tells us something about its size and ecological position. A smaller animal with that degree of forelimb impairment would have been far more vulnerable to predation and starvation. At 300-plus kilograms, as the largest predator in its ecosystem, Dilophosaurus had a buffer that smaller animals did not. Its right third finger was permanently deformed and could no longer flex, yet the animal carried on.
The Jurassic Park Problem
No discussion of Dilophosaurus size is complete without addressing the elephant in the room, or rather, the lack of one. In the 1993 film Jurassic Park, Dilophosaurus was depicted as a small animal, roughly the size of a large dog, with a retractable frill around its neck and the ability to spit venom at its prey. Every one of these features is fiction. There is no fossil evidence for a neck frill, no evidence for venom glands or venom-delivery structures, and the real animal was not small. A fully grown Dilophosaurus stood taller than an adult human at the hip and weighed as much as a large horse.
The filmmakers made a deliberate creative choice to shrink the animal so it would not be confused with the Velociraptors, which were themselves dramatically enlarged beyond their real size. The result is that an entire generation grew up thinking of Dilophosaurus as a small, somewhat comical creature. The 2020 monograph’s lead author, Adam Marsh, has spoken publicly about the challenge of correcting this perception. The real Dilophosaurus was a serious, large-bodied predator, and the anatomical work of the past few years has only reinforced that picture.
Where Dilophosaurus Fits in the Size Story of Theropods
Theropod dinosaurs started small. The earliest members of the lineage in the Late Triassic were lightly built animals, often just a meter or two in length. Something changed around the Triassic-Jurassic boundary, roughly 201 million years ago. Dilophosaurus appears right after that boundary, and its skeleton shows derived features in the axial column that researchers have linked to the broader trend of increasing body size and the shift toward macropredation in Theropoda.1Journal of Paleontology. A comprehensive anatomical and phylogenetic evaluation of Dilophosaurus wetherilli (Dinosauria, Theropoda) with descriptions of new specimens from the Kayenta Formation of northern Arizona
Dilophosaurus sits at an interesting point in this trajectory. It was not yet as large as the theropods that would dominate later Jurassic ecosystems, but it was dramatically larger than anything that came before it on the same continent. Its closest relatives in the phylogenetic analysis, animals like Cryolophosaurus from Antarctica and Zupaysaurus from Argentina, were also large-bodied, crested theropods from roughly the same time period. This suggests that the Early Jurassic saw a burst of body-size evolution among this particular lineage of theropods, possibly enabled by the ecological vacuum left after the end-Triassic extinction removed competing large predators.
The vertebral adaptations that appear in Dilophosaurus, those bony “shoulders” on the neural spines, are part of a broader pattern. As theropods got bigger through the Jurassic and Cretaceous, their vertebral columns developed increasingly elaborate structures to handle the mechanical demands of supporting a larger body. Dilophosaurus represents an early chapter in that story, where the skeleton was already being modified in response to size but had not yet reached the extremes seen in later giants. For anyone trying to understand the arc of theropod evolution, Dilophosaurus is less a curiosity and more a keystone: the point where big theropods first became a serious presence on the landscape.