Dilophosaurus

Dilophosaurus inhabited the semi-arid fluvial plain of the Kayenta Formation in the Early Jurassic, a region with rainy summers and dry winters, crossed by low-gradient meandering rivers and seasonal lakes. The environment was dominated by ferns and primitive conifers. Other inhabitants included the small armored dinosaur Scutellosaurus, the sauropodomorph Sarahsaurus, the pterosaur Rhamphinion, crocodyliformes, and the first true mammals of North America.

As the apex predator of its ecosystem, Dilophosaurus hunted large prey like Sarahsaurus and likely also smaller prey like Scutellosaurus. The Marsh and Rowe (2020) revision demonstrated that its jaws were robust enough to puncture bone, overturning the weak predator hypothesis. The subnarial gap (opening between premaxilla and maxilla) may have facilitated prey hooking. Evidence of scavenging behavior on Sarahsaurus carcasses has also been documented.

The paired skull crests, too thin for combat, were likely used for visual display: species recognition, status signaling, and sexual attractiveness. The infant specimen MNA P1.3181 and multiple known adults suggest Dilophosaurus may have lived in family groups or tolerated other individuals at resource sites. Bone pathologies in the holotype indicate intraspecific combat or accidents during hunting. The bird-like resting posture documented by fossilized tracks suggests more avian than reptilian behavior.

The pneumatized cervical vertebrae of Dilophosaurus indicate a system of air sacs connected to the lungs, similar to the respiratory system of modern birds, suggesting high metabolic efficiency and likely endothermic (warm-blooded) metabolism. The estimated growth rate of 30 to 35 kg per year early in life indicates rapid growth typical of endotherms. Hollow bones reduced weight without sacrificing structural strength, an adaptation that would reach its apex in modern birds.

The founding paper of Dilophosaurus. Sam Welles describes three theropod skeletons excavated in 1942 from the Kayenta Formation of Arizona, naming the species Megalosaurus wetherilli in honor of Navajo guide John Wetherill. The material included holotype UCMP 37302, a nearly complete skeleton, and paratype UCMP 37303. Welles had not yet recognized the skull crests, as the specimen had been damaged during preparation. The assignment to the wastebasket genus Megalosaurus would be corrected 16 years later.

Holotype skull of Dilophosaurus wetherilli (UCMP 37302) in right lateral view, showing the prominent nasolacrimal crests. Illustration by Marsh and Rowe (2020), based on the same specimen described by Welles in 1954.

Map of localities where Dilophosaurus wetherilli specimens were collected in northern Arizona, within the Navajo Nation area.

Key paper in which Welles establishes the new genus Dilophosaurus after examining a larger specimen collected in 1964 and recognizing the paired skull crests that had been destroyed during preparation of the original holotype. The generic name, from Greek di (two), lophos (crest) and sauros (lizard), perfectly describes the animal's most distinctive diagnostic feature. This short publication establishes Dilophosaurus wetherilli as an independent species and paves the way for the complete 1984 revision.

Paratype skull of Dilophosaurus wetherilli (UCMP 37303), showing the articulated maxilla and premaxilla in multiple views. The nasolacrimal crests are the diagnostic element that prompted the genus establishment in 1970.

Comparison of the subnarial gap (opening between premaxilla and maxilla) in Baryonyx (yellow), Coelophysis (green) and Dilophosaurus (cyan). This structure is one of the most discussed anatomical features in the taxonomic history of the genus.

A 185-page monograph that served as the definitive anatomical reference for Dilophosaurus for 36 years, until the Marsh and Rowe (2020) revision. Welles describes in detail the bones of the holotype and referred specimens, compares the animal with other theropods known at the time, and discusses its phylogeny. The work consolidates Dilophosaurus as a well-founded independent taxon and documents its osteological anatomy with unprecedented detail for the period. Many of Welles's interpretations were later revised by the 2020 analysis.

Cervical vertebrae 4 through 14 of the Dilophosaurus holotype (UCMP 37302) in left and right lateral views, with detailed anatomical labels. These hollow vertebrae were one of the adaptations to macropredation described by classical anatomy.

Atlas and axis bones of the Dilophosaurus wetherilli holotype in multiple views. The anterior cervical vertebrae contain air sacs (pneumatization), a feature shared with modern birds.

Biomechanical study that analyzed mandibular force profiles of multiple theropods using beam-theory models, including Dilophosaurus wetherilli. Results indicated that Dilophosaurus bite force decreased rapidly along the tooth row, with anterior teeth being the strongest. This suggested adaptation for capturing and holding relatively smaller prey. The study also linked the subnarial gap to a specialized biting strategy, with middle teeth executing cuts while front teeth held prey.

Dilophosaurus skull at the American Museum of Natural History (AMNH), showing the subnarial gap between premaxilla and maxilla, a central structure in biomechanical bite force studies of this animal.

Cranial reconstruction of Dilophosaurus wetherilli in right lateral view, based on multiple UCMP and TMM specimens. The structure of the nasolacrimal crests and the subnarial gap are visible in this reconstruction by Brian Engh (2020).

Joint mobility study that examined the range of motion of forelimbs in basal theropods, including Dilophosaurus wetherilli. Results showed Dilophosaurus could retract the humerus nearly parallel to the scapula but could not raise it vertically. The range of motion was consistent with bilateral grasping and the ability to hold objects against the chest or neck base. The study revealed Dilophosaurus used its front claws to hook and immobilize prey, not for locomotory support.

Right and left humeri of the Dilophosaurus holotype (UCMP 37302) in six anatomical views. The prominent deltopectoral crest indicates powerful forelimb musculature, compatible with predatory use.

Radii and ulnae (left and right) of the Dilophosaurus holotype in multiple views. Detailed analysis of these bones allowed reconstruction of elbow and wrist range of motion.

A study dedicated exclusively to the forelimbs of Dilophosaurus wetherilli, describing the range of motion of each joint from shoulder to digit, with particular attention to paleopathologies affecting the holotype's movements. The authors also describe a previously unreported distal carpal bone. Conclusions confirm that Dilophosaurus had functional forelimbs for prey grasping, but with limited shoulder mobility, requiring the mouth to make first contact during attacks. The role of venom and frills, as in Jurassic Park, is entirely rejected.

Scapulae and coracoids of the Dilophosaurus holotype (UCMP 37302) in six anatomical views. The morphology of these elements was key to establishing the animal's limited shoulder elevation.

Skeletal pathologies identified in the Dilophosaurus wetherilli holotype. Healed lesions indicate the animal survived physical trauma, revealing behavior and skeletal vulnerabilities from the challenges of predation.

Description of previously undescribed specimens of Dilophosaurus wetherilli from the Kayenta Formation of northern Arizona. Gay documents anatomical material not previously described, expanding the known fossil record of the species before the comprehensive Marsh and Rowe revision. The work includes observations on individual variation among specimens and raises questions about sexual dimorphism and ontogenetic growth in the genus. Despite being published in a lower-circulation volume, the paper contributes relevant raw data incorporated in the 2020 analysis.

Ilia referred to Dilophosaurus wetherilli in multiple anatomical views. The ilia are crucial pelvic elements for determining posture, locomotion, and phylogenetic classification of theropods.

Ischia and pubes referred to Dilophosaurus in detailed views. Pelvic morphology is one of the most important phylogenetic characters used in classifying Early Jurassic theropods.

Description of Notatesseraeraptor frickensis, a new Late Triassic theropod from Switzerland. The accompanying phylogenetic analysis places Dilophosaurus wetherilli as a non-averostran neotheropod, forming a grade with other basal forms relative to Averostra. This paper was one of the first to formally demonstrate that Dilophosaurus does not belong to Coelophysoidea or Ceratosauria, corroborating earlier analyses and establishing the phylogenetic baseline confirmed by Marsh and Rowe (2020).

Evolution of the avian ankle in theropods. This morphological analysis reveals the patterns of anatomical transition that allow Dilophosaurus to be placed in the basal neotheropod lineage, before the emergence of Averostra.

Trunk vertebrae (V15-V24) of Dilophosaurus in lateral and dorsal views. Vertebral anatomy is one of the most informative character sets in phylogenetic analyses of basal theropods.

The most comprehensive redescription ever published on Dilophosaurus wetherilli, spanning 103 pages covering holotype, referred, and new specimens. Marsh and Rowe demonstrate that Dilophosaurus had robust jaws strong enough to puncture bone, overturning the perception it was a weak predator. Phylogenetic analysis confirms its position as a non-averostran neotheropod, sister to Averostra, and more derived than Cryolophosaurus. The paper also documents bone pathologies, ontogenetic growth, and the infant specimen MNA P1.3181. It is the definitive modern reference for the taxon.

Map of Kayenta Formation localities from which Dilophosaurus wetherilli was collected in northern Arizona, with an inset stratigraphic column. Published by Marsh and Rowe in 2020 in the Journal of Paleontology.

CT volume renderings of the braincase referred to Dilophosaurus wetherilli, with matrix digitally removed. The CT scan revealed internal details of the neurocranium impossible to observe without destroying the fossil.

The axial skeleton osteological component within the comprehensive 2020 revision, describing in detail the cervical, dorsal, sacral and caudal vertebrae of Dilophosaurus wetherilli. Analysis reveals that cervical vertebrae were pneumatized with air sacs, considered an ancestral feature of birds representing early evolution of the high-efficiency respiratory system seen in modern birds. Axial skeleton data were used to calculate total length and body mass of known specimens.

Sacral vertebrae (V24-V28), haemal arches, and three blocks of gastralia of Dilophosaurus in multiple views. Gastralia are ventral belly bones that may have aided in respiration and protection of internal organs.

Articulated right hindlimb of Dilophosaurus, including femur, tibia, fibula, tarsus, and pes. The robustness of the femur and foot morphology confirm efficient bipedal locomotion and possibly high speed.

Three-dimensional analysis of theropod trackways from Connecticut Valley, including large Eubrontes traces attributed to Dilophosaurus-grade theropods. The study used 3D scanning to reconstruct foot kinematics during locomotion, revealing that these large Early Jurassic theropods kept their feet highly flexed during gait. Eubrontes tracks are Connecticut's state dinosaur and likely represent the locomotory trace of Dilophosaurus or very similar animals.

Reconstruction of Dilophosaurus in the background with the pterosaur Rhamphinion in the foreground, contemporary fauna from the Kayenta Formation. These animals shared the same Early Jurassic environment in Arizona.

Size comparison between the two known Dilophosaurus wetherilli specimens and a human. The holotype (smaller) and the 1964 adult specimen (larger) show the size range of the species.

Description of a new species of the theropod Syntarsus (now Megapnosaurus) from the Kayenta Formation of Arizona, the small predator that coexisted with Dilophosaurus. The paper documents contemporary fauna and establishes the paleoecological context of the Early Jurassic in Arizona: an ecosystem with one large apex predator (Dilophosaurus) and multiple smaller carnivores competing for the same territory. Associated fauna also included the dinosaurs Sarahsaurus and Scutellosaurus, along with pterosaurs, crocodyliformes, and primitive mammals.

Artistic reconstruction of Dilophosaurus chasing Scutellosaurus, the small armored dinosaur that shared the Kayenta Formation ecosystem in the Early Jurassic of Arizona.

Reconstruction of an adult Dilophosaurus tending to its hatching clutch. Parental care behavior inferred from patterns observed in other theropods and the infant specimen MNA P1.3181.

Radiometric dating using detrital zircons from the Kayenta Formation yielded a U-Pb age of 183.7 ±2.7 Ma, the first direct depositional radiometric date from the formation. This result shifted the dating of Dilophosaurus from Sinemurian-Pliensbachian to Pliensbachian-Toarcian, making it younger than previously thought. Geological data also reveal that the formation was deposited in a fluvial plain environment dominated by low-gradient meandering rivers, with seasonal lakes and pteridophyte forests.

Life reconstruction of Dilophosaurus wetherilli based on the Marsh and Rowe (2020) anatomical revision, by Petr Menshikov. The image reflects current scientific consensus on the animal's appearance, without frill or venom.

Reconstruction of Dilophosaurus wetherilli in a bird-like resting posture. Based on fossilized resting traces (SGDS 18.T1) and published in a 2009 PLOS ONE article.

Comprehensive review of Early Jurassic dinosaurs from the Hanson Formation of Antarctica, including Cryolophosaurus ellioti, the closest confirmed relative of Dilophosaurus. Phylogenetic analysis positions Dilophosaurus and Cryolophosaurus in a clade of pre-Averostra basal theropods, clarifying that cranial crests evolved independently in multiple Early Jurassic theropod lineages. The paper establishes the biogeographic context of the radiation of large-crested theropods during the Early Jurassic across Gondwana and Laurasia.

Official 2024 National Fossil Day artwork from the US National Park Service, depicting Dilophosaurus wetherilli and Scutellosaurus. The representation reflects the current state of scientific knowledge about these Early Jurassic animals.

Dilophosaurus wetherilli infographic with data on size, weight, period, diet, and main anatomical features. The size comparison includes a human silhouette for scale reference.

Documents the status of Dilophosaurus wetherilli as the largest known theropod from the Early Jurassic of North America. The work compares Dilophosaurus with other large predators of the period, discusses its ecological role as apex predator in an ecosystem dominated by protodinosaurs and synapsids, and contextualizes Museum of Northern Arizona findings relative to Californian university specimens. Dilophosaurus was literally the 'king' of North America before the rise of large ceratosaurs and tetanurans.

Mounted skeleton of Dilophosaurus at the Royal Tyrrell Museum of Palaeontology, Drumheller, Alberta, Canada. The mount shows the impressive stature of the largest land predator in North America during the Early Jurassic.

Black and white illustration of Dilophosaurus wetherilli with hypothetical plumage, showing how scientific artists explore the possibility of feathers in basal theropods based on analogies with coelurosaurs.

Full-size T-rex animatronic from the Jurassic Park franchise, with the iconic red Jeep — Amaury Laporte · CC BY 2.0