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''Dilophosaurus'' ( ) is a genus of theropod dinosaurs that lived in what is now
North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...
during the Early Jurassic, about 193 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 Samuel Paul Welles (November 9, 1907 – August 6, 1997) was an American palaeontologist. Welles was a research associate at the Museum of Palaeontology, University of California, Berkeley. He took part in excavations at the Placerias Quarry in ...
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, a
Navajo The Navajo (; British English: Navaho; nv, Diné or ') are a Native American people of the Southwestern United States. With more than 399,494 enrolled tribal members , the Navajo Nation is the largest federally recognized tribe in the United ...
councilor. Further specimens have since been found, including an infant. 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 Coelophysidae is a family of primitive carnivorous theropod dinosaurs. Most species were relatively small in size. The family flourished in the Late Triassic and Early Jurassic periods, and has been found on numerous continents. Many members of C ...
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 Intra-species recognition is the recognition by a member of a species of a conspecific (another member of the same species). In many species, such recognition is necessary for procreation. Different species may employ different methods, but all ...
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''. ''Dilophosaurus'' was featured in the novel ''
Jurassic Park ''Jurassic Park'', later also referred to as ''Jurassic World'', is an American science fiction media franchise created by Michael Crichton and centered on a disastrous attempt to create a theme park of cloned dinosaurs. It began in 1990 when ...
'' and its
movie adaptation A film adaptation is the transfer of a work or story, in whole or in part, to a feature film. Although often considered a type of derivative work, film adaptation has been conceptualized recently by academic scholars such as Robert Stam as a dia ...
, wherein it was given the fictional abilities to spit venom and expand a neck frill, as well as being smaller than the real animal. It was designated as the
state dinosaur State may refer to: Arts, entertainment, and media Literature * '' State Magazine'', a monthly magazine published by the U.S. Department of State * ''The State'' (newspaper), a daily newspaper in Columbia, South Carolina, United States * ''Our ...
of Connecticut based on tracks found there.


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 (UCMP) in search of fossil vertebrates in Navajo County in northern Arizona. Word of this was spread among the Native Americans there, and the
Navajo The Navajo (; British English: Navaho; nv, Diné or ') are a Native American people of the Southwestern United States. With more than 399,494 enrolled tribal members , the Navajo Nation is the largest federally recognized tribe in the United ...
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 Cameron may refer to: People * Clan Cameron, a Scottish clan * Cameron (given name), a given name (including a list of people with the name) * Cameron (surname), a surname (including a list of people with the name) ;Mononym * Cam'ron (born 197 ...
near Tuba City in the
Navajo Indian Reservation The Navajo Nation ( nv, Naabeehó Bináhásdzo), also known as Navajoland, is a Native American reservation in the United States. It occupies portions of northeastern Arizona, northwestern New Mexico, and southeastern Utah; at roughly , the ...
. Three dinosaur skeletons were found in purplish
shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4) and tiny fragments (silt-sized particles) of other minerals, especial ...
, 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 Relief is a sculptural method in which the sculpted pieces are bonded to a solid background of the same material. The term ''relief'' is from the Latin verb ''relevo'', to raise. To create a sculpture in relief is to give the impression that the ...
, 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 Samuel Paul Welles (November 9, 1907 – August 6, 1997) was an American palaeontologist. Welles was a research associate at the Museum of Palaeontology, University of California, Berkeley. He took part in excavations at the Placerias Quarry in ...
, 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 (catalogued as UCMP 37302) was made the holotype of the species, and the second specimen (UCMP 37303) was made the paratype. The
specific name Specific name may refer to: * in Database management systems, a system-assigned name that is unique within a particular database In taxonomy, either of these two meanings, each with its own set of rules: * Specific name (botany), the two-part (bino ...
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 (it had been suggested to be Late Triassic in age, whereas Welles thought it was
Early Early may refer to: History * The beginning or oldest part of a defined historical period, as opposed to middle or late periods, e.g.: ** Early Christianity ** Early modern Europe Places in the United States * Early, Iowa * Early, Texas * Early ...
to
Middle Jurassic The Middle Jurassic is the second epoch of the Jurassic Period. It lasted from about 174.1 to 163.5 million years ago. Fossils of land-dwelling animals, such as dinosaurs, from the Middle Jurassic are relatively rare, but geological formations co ...
), and discovered another skeleton about south of where the 1942 specimens had been found. The nearly complete specimen (catalogued as UCMP 77270) was collected with the help of
William J. Breed William J. "Bill" Breed (August 3, 1928 - January 22, 2013) was an American geologist, paleontologist, naturalist and author in Northern Arizona. He was a renowned expert on the geology of the Grand Canyon. Personal life William J. Breed was ...
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 had been pulled out of its position by a
scavenger Scavengers are animals that consume dead organisms that have died from causes other than predation or have been killed by other predators. While scavenging generally refers to carnivores feeding on carrion, it is also a herbivorous feeding b ...
. 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'' (''δι'') meaning "two", ''lophos'' (''λόφος'') 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 Robert Joseph Gay is an American Paleontologist known for his work in the Chinle and Kayenta Formations in the southwest United States. He is known for the discovery of the first occurrence of ''Crosbysaurus'' from Utah,Gay, R. J., & Aude, I. S. ...
identified the remains of at least three new ''Dilophosaurus'' specimens (this number is based on the presence of three pubic bone fragments and two differentially sized femora) 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 (MNA P1.3181), 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 (TMM 43646-140) 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.


Formerly assigned species

In 1984, Welles suggested that the 1964 specimen (UCMP 77270) did not belong to ''Dilophosaurus'', but to a new genus, based on differences in the skull, vertebrae, and femora. He maintained that both genera bore crests, but that the exact shape of these was unknown in ''Dilophosaurus''. Welles died in 1997, before he could name this supposed new dinosaur, and the idea that the two were separate genera has generally been ignored or forgotten since. In 1999, amateur paleontologist Stephan Pickering privately published the new name ''Dilophosaurus'' "breedorum" based on the 1964 specimen, named in honor of Breed, who had assisted in collecting it. This name is considered a''
nomen nudum In taxonomy, a ''nomen nudum'' ('naked name'; plural ''nomina nuda'') is a designation which looks exactly like a scientific name of an organism, and may have originally been intended to be one, but it has not been published with an adequate descr ...
'', an invalidly published name, and Gay pointed out in 2005 that no significant differences exist between ''D''. "breedorum" and other ''D. wetherilli'' specimens. In 2012, Carrano and colleagues found differences between the 1964 specimen and the holotype specimen, but attributed them to variation between individuals rather than species. Paleontologists Christophe Hendrickx and Octávio Mateus suggested in 2014 that the known specimens might represent two species of ''Dilophosaurus'' based on different skull features and stratigraphic separation, pending thorough description of assigned specimens. Marsh and Rowe concluded in 2020 that there was only one taxon among known ''Dilophosaurus'' specimens, and that differences between them were due to their different degree of maturity and preservation. They did not find considerable stratigraphic separation between the specimens either. A nearly complete theropod skeleton (KMV 8701) was discovered in the Lufeng Formation, in Yunnan Province, China, in 1987. It is similar to ''Dilophosaurus'', with a pair of crests and a gap separating the premaxilla from the maxilla, but differs in some details. The paleontologist Shaojin Hu named it as a new species of ''Dilophosaurus'' in 1993, ''D. sinensis'' (from Greek ''Sinai'', referring to China). In 1998, the paleontologist Matthew C. Lamanna and colleagues found ''D. sinensis'' to be identical to ''
Sinosaurus triassicus ''Sinosaurus'' (meaning "Chinese lizard") is an extinct genus of theropod dinosaur which lived during the Early Jurassic Period. It was a bipedal carnivore approximately in length and in body mass. Fossils of the animal were found at the ...
'', a theropod from the same formation, named in 1940. This conclusion was confirmed by paleontologist Lida Xing and colleagues in 2013, and though paleontologist Guo-Fu Wang and colleagues agreed the species belonged in ''Sinosaurus'' in 2017, they suggested it may be a separate species, ''S. sinensis''.


Description

''Dilophosaurus'' was one of the earliest large predatory
dinosaurs Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...
, a medium-sized theropod, though small compared to some of the later theropods. It was also the largest known land-animal of North America during the Early Jurassic. Slender and lightly built, its size was comparable to that of a brown bear. The largest known specimen weighed about , measured about in length, and its skull was long. The smaller holotype specimen weighed about , was long, with a hip height of about , and its skull was long. A resting trace of a theropod similar to ''Dilophosaurus'' and ''
Liliensternus ''Liliensternus'' is an extinct genus of basal neotheropod dinosaur that lived approximately 210 million years ago during the latter part of the Triassic Period in what is now Germany. ''Liliensternus'' was a moderate-sized, bipedal, ground-dwel ...
'' has been interpreted by some researchers as showing impressions of feathers around the belly and feet, similar to
down Down most often refers to: * Down, the relative direction opposed to up * Down (gridiron football), in American/Canadian football, a period when one play takes place * Down feather, a soft bird feather used in bedding and clothing * Downland, a ty ...
. Other researchers instead interpret these impressions as
sedimentological Sedimentology encompasses the study of modern sediments such as sand, silt, and clay, and the processes that result in their formation (erosion and weathering), transport, deposition and diagenesis. Sedimentologists apply their understanding of mo ...
artifacts created as the dinosaur moved, though this interpretation does not rule out that the track-maker could have borne feathers.


Skull

The skull of ''Dilophosaurus'' was large in proportion to the overall skeleton, yet delicate. The snout was narrow in front view, becoming narrower towards the rounded top. The premaxilla (front bone of the upper jaw) was long and low when seen from the side, bulbous at the front, and its outer surface became less convex from snout to naris (bony nostril). The nostrils were placed further back than in most other theropods. The premaxillae were in close articulation with each other, and while the premaxilla only connected to the maxilla (the following bone of the upper jaw) at the middle of the palate, with no connection at the side, they formed a strong joint through the robust, interlocking articulation between the hindwards and forwards directed processes of these bones. Hindwards and below, the premaxilla formed a wall for a gap between itself and the maxilla called the subnarial gap (also termed a "kink"). Such a gap is also present in
coelophysoids Coelophysoidea were common dinosaurs of the Late Triassic and Early Jurassic periods. They were widespread geographically, probably living on all continents. Coelophysoids were all slender, carnivorous forms with a superficial similarity to the ...
, as well as other dinosaurs. The subnarial gap resulted in a diastema, a gap in the tooth row (which has also been called a "notch"). Within the subnarial gap was a deep excavation behind the toothrow of the premaxilla, called the subnarial pit, which was walled by a downwards keel of the premaxilla. The outer surface of the premaxilla was covered in foramina (openings) of varying sizes. The upper of the two backward-extending processes of the premaxilla was long and low, and formed most of the upper border of the elongated naris. It had a dip towards the font, which made the area by its base concave in profile. The underside of the premaxilla containing the
alveoli Alveolus (; pl. alveoli, adj. alveolar) is a general anatomical term for a concave cavity or pit. Uses in anatomy and zoology * Pulmonary alveolus, an air sac in the lungs ** Alveolar cell or pneumocyte ** Alveolar duct ** Alveolar macrophage * ...
(tooth sockets) was oval. The maxilla was shallow, and was depressed around the antorbital fenestra (a large opening in front of the eye), forming a recess that was rounded towards the front, and smoother than the rest of the maxilla. A foramen called the preantorbital fenestra opened into this recess at the front bend. Large foramina ran on the side of the maxilla, above the alveoli. A deep nutrient groove ran backward from the subnarial pit along the base of the
interdental plates The interdental plate refers to the bone-filled mesial-distal region between the teeth. The word "''interdental''" is a combination of "''inter''" + "''dental''" (meaning "''between the teeth''") which originated in approximately 1870. In paleobi ...
(or rugosae) of the maxilla. ''Dilophosaurus'' bore a pair of high, thin, and arched (or plate-shaped) crests longitudinally on the skull roof. The crests (termed the nasolacrimal crests) began as low ridges on the premaxillae and were mainly formed by the upwards expanded and . These bones were
coossified Ossification (also called osteogenesis or bone mineralization) in bone remodeling is the process of laying down new bone material by cells named osteoblasts. It is synonymous with bone tissue formation. There are two processes resulting in ...
together (fusion during bone tissue formation), so the sutures between them cannot be determined. The lacrimal bone expanded into a thick, rugose boss, forming an arc at the upper front border of the orbit (eye socket), and supported the bottom of the back of the crest. Uniquely for this genus, the rim above the orbit continued hindwards and ended in a small, almost triangular process behind the orbit, which curved slightly outwards. Since only a short part of the upper surface of this process is unbroken, the rest of the crest may have risen above the skull over a distance of ~. The preserved part of the crest in UCMP 77270 is tallest around the midpoint of the antorbital fenestra's length. UCMP 77270 preserves the concave shelf between the bases of the crests, and when seen from the front, they projected upwards and to the sides at an ~80° angle. Welles found the crests reminiscent of a double-crested cassowary, while Marsh and Rowe stated they were probably covered in keratin or keratinized skin. They pointed out that by comparison with helmeted guineafowl, the keratin on the crests of ''Dilophosaurus'' could have enlarged them much more than what is indicated by the bone. As only one specimen preserves much of the crests, whether they differed between individuals is unknown.
CT scans A computed tomography scan (CT scan; formerly called computed axial tomography scan or CAT scan) is a medical imaging technique used to obtain detailed internal images of the body. The personnel that perform CT scans are called radiographers ...
show that air sacs (pockets of air that provide strength for and lighten bones) were present in the bones that surrounded the brain, and were continuous with the sinus cavities in the front of the skull. The antorbital fenestra was continuous with the side of the crests, which indicates the crests also had air sacs (a ridge of bone forms a roof over the antorbital fenestrae in most other theropods). The orbit was oval, and narrow towards the bottom. The
jugal bone The jugal is a skull bone found in most reptiles, amphibians and birds. In mammals, the jugal is often called the malar or zygomatic. It is connected to the quadratojugal and maxilla, as well as other bones, which may vary by species. Anatomy ...
had two upwards pointing processes, the first of which formed part of the lower margin of the antorbital fenestra, and part of the lower margin of the orbit. A projection from the quadrate bone into the
lateral temporal fenestra An infratemporal fenestra, also called the lateral temporal fenestra or simply temporal fenestra, is an opening in the skull behind the orbit in some animals. It is ventrally bordered by a zygomatic arch. An opening in front of the eye sockets ...
(opening behind the eye) gave this a
reniform Reniform is an adjective meaning "kidney-shaped" and may specifically refer to: * Reniform leaf The following is a list of terms which are used to describe leaf morphology in the description and taxonomy of plants. Leaves may be simple (a single ...
(kidney-shaped) outline. The
foramen magnum The foramen magnum ( la, great hole) is a large, oval-shaped opening in the occipital bone of the skull. It is one of the several oval or circular openings (foramina) in the base of the skull. The spinal cord, an extension of the medulla oblon ...
(the large opening at the back of the
braincase In human anatomy, the neurocranium, also known as the braincase, brainpan, or brain-pan is the upper and back part of the skull, which forms a protective case around the brain. In the human skull, the neurocranium includes the calvaria or skul ...
) was about half the breadth of the occipital condyle, which was itself cordiform (heart-shaped), and had a short neck and a groove on the side. The mandible was slender and delicate at the front, but the articular region (where it connected with the skull) was massive, and the mandible was deep around the
mandibular fenestra The skull is a bone protective Cranial cavity, cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible ...
(an opening on its side). The mandibular fenestra was small in ''Dilophosaurus'', compared to that of coelophysoids, and reduced from front to back, uniquely for this genus. The
dentary bone In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower teeth in place. The mandible sits beneath the maxilla. It is the only movable bone ...
(the front part of the mandible where most of the teeth there were attached) had an up-curved rather than pointed chin. The chin had a large foramen at the tip, and a row of small foramina ran in rough parallel with the upper edge of the dentary. On the inner side, the
mandibular symphysis In human anatomy, the facial skeleton of the skull the external surface of the mandible is marked in the median line by a faint ridge, indicating the mandibular symphysis (Latin: ''symphysis menti'') or line of junction where the two lateral halves ...
(where the two halves of the lower jaw connected) was flat and smooth, and showed no sign of being fused with its opposite half. A
Meckelian foramen The Meckelian groove (or Meckel's groove, Meckelian fossa, or Meckelian foramen, or Meckelian canal) is an opening in the medial (inner) surface of the mandible (lower jaw) which exposes the Meckelian cartilage.retroarticular process of the mandible (a backwards projection) was long. ''Dilophosaurus'' had four teeth in each premaxilla, 12 in each maxilla, and 17 in each dentary. The teeth were generally long, thin, and recurved, with relatively small bases. They were compressed sideways, oval in cross-section at the base, lenticular (lens-shaped) above, and slightly concave on their outer and inner sides. The largest tooth of the maxilla was either in or near the fourth alveolus, and the height of the tooth crowns decreased hindwards. The first tooth of the maxilla pointed slightly forwards from its alveolus because the lower border of the prexamilla process (which projected backward towards the maxilla) was upturned. The teeth of the dentary were much smaller than those of the maxilla. The third or fourth tooth in the dentary of ''Dilophosaurus'' and some coelophysoids was the largest there, and seems to have fit into the subnarial gap of the upper jaw. Most of the teeth had serrations on the front and back edges, which were offset by vertical grooves, and were smaller at the front. About 31 to 41 serrations were on the front edges, and 29 to 33 were on the back. At least the second and third teeth of the premaxilla had serrations, but the fourth tooth did not. The teeth were covered in a thin layer of enamel, thick, which extended far towards their bases. The alveoli were elliptical to almost circular, and all were larger than the bases of the teeth they contained, which may therefore have been loosely held in the jaws. Though the number of alveoli in the dentary would seem to indicate that the teeth were very crowded, they were rather far apart, due to the larger size of their alveoli. The jaws contained
replacement teeth A polyphyodont is any animal whose teeth are continually replaced. In contrast, diphyodonts are characterized by having only two successive sets of teeth. Polyphyodonts include most toothed fishes, many reptiles such as crocodiles and geckos, and ...
at various stages of eruption. The interdental plates between the teeth were very low.


Postcranial skeleton

''Dilophosaurus'' had 10 cervical (neck), 14 dorsal (back), and 45 caudal (tail) vertebrae, and air sacs grew into the vertebrae. It had a long neck, which was probably flexed nearly 90° by the skull and by the shoulder, holding the skull in a horizontal posture. The cervical vertebrae were unusually light; their centra (the "bodies" of the vertebrae) were hollowed out by pleurocoels (depressions on the sides) and centrocoels (cavities on the inside). The arches of the cervical vertebrae also had
pneumatic Pneumatics (from Greek ‘wind, breath’) is a branch of engineering that makes use of gas or pressurized air. Pneumatic systems used in Industrial sector, industry are commonly powered by compressed air or compressed inert gases. A central ...
fossae (or chonoses), conical recesses so large that the bones separating them were sometimes paper-thin. The centra were plano-concave, flat to weakly convex at the front and deeply cupped (or concave) at the back, similar to '' Ceratosaurus''. This indicates that the neck was flexible, though it had long, overlapping cervical ribs, which were fused to the centra. The cervical ribs were slender and may have bent easily. The atlas bone (the first cervical vertebra which attaches to the skull) had a small, cubic centrum, and had a concavity at the front where it formed a cup for the occipital condyle (protuberance that connects with the atlas vertebra) at the back of the skull. The
axis bone In anatomy, the axis (from Latin ''axis'', "axle") or epistropheus is the second cervical vertebra (C2) of the spine, immediately inferior to the atlas, upon which the head rests. The axis' defining feature is its strong odontoid process (bon ...
(the second cervical vertebra) had a heavy spine, and its postzygapophyses (the processes of the vertebrae that articulated with the prezygapophyses of a following vertebrae) were met by long prezygapophyses that curved upwards from the third cervical vertebra. The centra and neural spines of the cervical vertebrae were long and low, and the spines were stepped in side view, forming "shoulders" at the front and back, as well as taller, central "caps" that gave the appearance of a
Maltese cross The Maltese cross is a cross symbol, consisting of four " V" or arrowhead shaped concave quadrilaterals converging at a central vertex at right angles, two tips pointing outward symmetrically. It is a heraldic cross variant which developed f ...
(cruciform) when seen from above, distinctive features of this dinosaur. The posterior centrodiapophyseal lamina of the cervicals showed serial variation, bifurcating and reuniting down the neck, a unique feature. The neural spines of the dorsal vertebrae were also low and expanded front and back, which formed strong attachments for ligaments. Uniquely for this genus, additional laminae emanated from the middle trunk vertebrae's anterior centrodiapophyseal laminae and posterior centrodiapophyseal laminae. The
sacral vertebrae The sacrum (plural: ''sacra'' or ''sacrums''), in human anatomy, is a large, triangular bone at the base of the spine that forms by the fusing of the sacral vertebrae (S1S5) between ages 18 and 30. The sacrum situates at the upper, back part ...
which occupied the length of the
ilium Ilium or Ileum may refer to: Places and jurisdictions * Ilion (Asia Minor), former name of Troy * Ilium (Epirus), an ancient city in Epirus, Greece * Ilium, ancient name of Cestria (Epirus), an ancient city in Epirus, Greece * Ilium Building, a ...
blade did not appear to be fused. The rib of the first sacral vertebra articulated with the preacetabular process of the ilium, a distinct feature. The centra of the caudal vertebrae were very consistent in length, but their diameter became smaller towards the back, and they went from elliptical to circular in cross-section. The scapulae (shoulder blades) were moderate in length and concave on their inner sides to follow the body's curvature. The scapulae were wide, particularly the upper part, which was rectangular (or squared off), a unique feature. The
coracoids A coracoid (from Greek κόραξ, ''koraks'', raven) is a paired bone which is part of the shoulder assembly in all vertebrates except therian mammals (marsupials and placentals). In therian mammals (including humans), a coracoid process is prese ...
were elliptical, and not fused to the scapulae. The lower hind portions of the coracoids had a "horizontal buttress" next to the biceps tuber, unique for this genus. The arms were powerful, and had deep pits and stout processes for attachment of muscles and ligaments. The
humerus The humerus (; ) is a long bone in the arm that runs from the shoulder to the elbow. It connects the scapula and the two bones of the lower arm, the radius and ulna, and consists of three sections. The humeral upper extremity consists of a roun ...
(upper arm bone) was large and slender, and the ulna (lower arm bone) was stout and straight, with a stout olecranon. The hands had four fingers: the first was shorter but stronger than the following two fingers, with a large claw, and the two following fingers were longer and slenderer, with smaller claws. The claws were curved and sharp. The third finger was reduced, and the fourth was vestigial (retained, but without function). The
crest Crest or CREST may refer to: Buildings *The Crest (Huntington, New York), a historic house in Suffolk County, New York *"The Crest", an alternate name for 63 Wall Street, in Manhattan, New York *Crest Castle (Château Du Crest), Jussy, Switzerla ...
of the ilium was highest over the ilial
peduncle Peduncle may refer to: *Peduncle (botany), a stalk supporting an inflorescence, which is the part of the shoot of seed plants where flowers are formed *Peduncle (anatomy), a stem, through which a mass of tissue is attached to a body **Peduncle (art ...
(the downwards process of the ilium), and its outer side was concave. The foot of the pubic bone was only slightly expanded, whereas the lower end was much more expanded on the
ischium The ischium () form ...
, which also had a very thin shaft. The hind legs were large, with a slighter longer femur (thigh bone) than tibia (lower leg bone), the opposite of, for example, ''Coelophysis''. The femur was massive; its shaft was sigmoid-shaped (curved like an 'S'), and its greater trochanter was centered on the shaft. The tibia had a developed
tuberosity In the skeleton of humans and other animals, a tubercle, tuberosity or apophysis is a protrusion or eminence that serves as an attachment for skeletal muscles. The muscles attach by tendons, where the enthesis is the connective tissue between the ...
and was expanded at the lower end. The
astragalus bone The talus (; Latin for ankle or ankle bone), talus bone, astragalus (), or ankle bone is one of the group of foot bones known as the tarsus. The tarsus forms the lower part of the ankle joint. It transmits the entire weight of the body from the ...
(ankle bone) was separated from the tibia and the
calcaneum In humans and many other primates, the calcaneus (; from the Latin ''calcaneus'' or ''calcaneum'', meaning heel) or heel bone is a bone of the tarsus of the foot which constitutes the heel. In some other animals, it is the point of the hock. St ...
, and formed half of the socket for the fibula. It had long, stout feet with three well-developed toes that bore large claws, which were much less curved than those of the hand. The third toe was the stoutest, and the smaller first toe (the hallux) was kept off the ground.


Classification

Welles thought ''Dilophosaurus'' a
megalosaur Megalosauroidea (meaning 'great/big lizard forms') is a superfamily (or clade) of tetanuran theropod dinosaurs that lived from the Middle Jurassic to the Late Cretaceous period. The group is defined as '' Megalosaurus bucklandii'' and all taxa s ...
in 1954, but revised his opinion in 1970 after discovering that it had crests. By 1974, Welles and the paleontologist Robert A. Long found ''Dilophosaurus'' to be a
ceratosauroid Ceratosaurs are members of the clade Ceratosauria, a group of dinosaurs defined as all theropods sharing a more recent common ancestor with '' Ceratosaurus'' than with birds. The oldest known ceratosaur, '' Saltriovenator'', dates to the earlie ...
. In 1984 Welles found that ''Dilophosaurus'' exhibited features of both Coelurosauria and Carnosauria, the two main groups into which theropods had hitherto been divided, based on body size, and he suggested this division was inaccurate. He found ''Dilophosaurus'' to be closest to those theropods that were usually placed in the family
Halticosauridae Coelophysoidea were common dinosaurs of the Late Triassic and Early Jurassic periods. They were widespread geographically, probably living on all continents. Coelophysoids were all slender, carnivorous forms with a superficial similarity to the ...
, particularly ''Liliensternus''. In 1988, paleontologist Gregory S. Paul classified the halticosaurs as a subfamily of the family
Coelophysidae Coelophysidae is a family of primitive carnivorous theropod dinosaurs. Most species were relatively small in size. The family flourished in the Late Triassic and Early Jurassic periods, and has been found on numerous continents. Many members of C ...
, and suggested that ''Dilophosaurus'' could have been a direct descendant of ''Coelophysis''. Paul also considered the possibility that
spinosaurs The Spinosauridae (or spinosaurids) are a clade or family of tetanuran theropod dinosaurs comprising ten to seventeen known genera. They came into prominence during the Cretaceous period. Spinosaurid fossils have been recovered worldwide, includin ...
were late-surviving dilophosaurs, based on similarity of the kinked snout, nostril position, and slender teeth of '' Baryonyx''. In 1994, paleontologist
Thomas R. Holtz Thomas Richard Holtz Jr. (born September 13, 1965) is an American vertebrate palaeontologist, author, and principal lecturer at the University of Maryland, College Park, University of Maryland's Department of Geology. He has published extensively ...
placed ''Dilophosaurus'' in the group Coelophysoidea, along with but separate from the Coelophysidae. He placed the Coelophysoidea in the group Ceratosauria. In 2000, paleontologist James H. Madsen and Welles divided Ceratosauria into the families
Ceratosauridae Ceratosauridae is an extinct family of theropod dinosaurs belonging to the infraorder Ceratosauria. The family's type genus, ''Ceratosaurus'', was first found in Jurassic rocks from North America. Ceratosauridae is made up of the genera ''Cerat ...
and Dilophosauridae, with ''Dilophosaurus'' as the sole member of the latter family. Lamanna and colleagues pointed out in 1998 that since ''Dilophosaurus'' was discovered to have had crests on its skull, other similarly crested theropods have been discovered (including ''Sinosaurus''), and that this feature is, therefore, not unique to the genus, and of limited use for determining interrelationships within their group. Paleontologist Adam M. Yates described the genus '' Dracovenator'' from South Africa in 2005, and found it closely related to ''Dilophosaurus'' and ''
Zupaysaurus ''Zupaysaurus'' (; "ZOO-pay-SAWR-us") is an extinct genus of early theropod dinosaur living during the Norian stage of the Late Triassic in what is now Argentina. Fossils of the dinosaur were found in the Los Colorados Formation of the Ischigu ...
''. His cladistic analysis suggested they did not belong in the Coelophysoidea, but rather in the Neotheropoda, a more
derived Derive may refer to: * Derive (computer algebra system), a commercial system made by Texas Instruments * ''Dérive'' (magazine), an Austrian science magazine on urbanism *Dérive, a psychogeographical concept See also * *Derivation (disambiguatio ...
(or "advanced") group. He proposed that if ''Dilophosaurus'' was more derived than the Coelophysoidea, the features it shared with this group may have been inherited from
basal Basal or basilar is a term meaning ''base'', ''bottom'', or ''minimum''. Science * Basal (anatomy), an anatomical term of location for features associated with the base of an organism or structure * Basal (medicine), a minimal level that is nec ...
(or "primitive") theropods, indicating that theropods may have passed through a "coelophysoid stage" in their early evolution. In 2007, paleontologist Nathan D. Smith and colleagues found the crested theropod '' Cryolophosaurus'' to be the sister species of ''Dilophosaurus'', and grouped them with ''Dracovenator'' and ''Sinosaurus''. This clade was more derived than the Coelophysoidea, but more basal than the Ceratosauria, thereby placing basal theropods in a ladder-like arrangement. In 2012, Carrano and colleagues found that the group of crested theropods proposed by Smith and colleagues was based on features that relate to the presence of such crests, but that the features of the rest of the skeleton were less consistent. They instead found that ''Dilophosaurus'' was a coelophysoid, with ''Cryolophosaurus'' and ''Sinosaurus'' being more derived, as basal members of the group Tetanurae. Paleontologist Christophe Hendrickx and colleagues defined the Dilophosauridae to include ''Dilophosaurus'' and ''Dracovenator'' in 2015, and noted that while general uncertainty exists about the placement of this group, it appears to be slightly more derived than the Coelophysoidea, and the sister group to the Averostra. The Dilophosauridae share features with the Coelophysoidea such as the subnarial gap and the front teeth of the maxilla pointing forwards, while features shared with Averostra include a fenestra at the front of the maxilla and a reduced number of teeth in the maxilla. They suggested that the cranial crests of ''Cryolophosaurus'' and ''Sinosaurus'' had either
evolved convergently Convergent evolution is the independent evolution of similar features in species of different periods or epochs in time. Convergent evolution creates analogous structures that have similar form or function but were not present in the last com ...
, or were a feature inherited from a common ancestor. The following cladogram is based on that published by Hendrickx and colleagues, itself based on earlier studies: In 2019, paleontologists Marion Zahner and Winand Brinkmann found the members of the Dilophosauridae to be successive basal sister taxa of the Averostra rather than a
monophyletic In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic gro ...
clade (a natural group), but noted that some of their analyses did find the group valid, containing ''Dilophosaurus'', ''Dracovenator'', ''Cryolophosaurus'', and possibly ''
Notatesseraeraptor ''Notatesseraeraptor'' ("feature mosaic tile thief"; from the Latin "nota", feature; "tesserae", tiles used to make a mosaic, in reference to the mixture of features normally found on dilophosaurids and coelophysoids; and "raptor", thief) is a g ...
'' as the basal-most member. They therefore provided a diagnosis for the Dilophosauridae, based on features in the lower jaw. In the phylogenetic analysis accompanying their 2020 redescription, Marsh and Rowe found all specimens of ''Dilophosaurus'' to form a monophyletic group, sister to Averostra, and more derived than ''Cryolophosaurus''. Their analysis did not find support for Dilophosauridae, and they suggested cranial crests were a
plesiomorphic In phylogenetics, a plesiomorphy ("near form") and symplesiomorphy are synonyms for an ancestral character shared by all members of a clade, which does not distinguish the clade from other clades. Plesiomorphy, symplesiomorphy, apomorphy, and ...
(ancestral) trait of Ceratosauria and Tetanurae.


Ichnology

Various ichnotaxa (taxa based on
trace fossils A trace fossil, also known as an ichnofossil (; from el, ἴχνος ''ikhnos'' "trace, track"), is a fossil record of biological activity but not the preserved remains of the plant or animal itself. Trace fossils contrast with body fossils, ...
) have been attributed to ''Dilophosaurus'' or similar theropods. In 1971, Welles reported dinosaur footprints from the Kayenta Formation of northern Arizona, on two levels and below where the original ''Dilophosaurus'' specimens were found. The lower footprints were
tridactyl In biology, dactyly is the arrangement of digits (fingers and toes) on the hands, feet, or sometimes wings of a tetrapod animal. It comes from the Greek word δακτυλος (''dáktylos'') = "finger". Sometimes the ending "-dactylia" is use ...
(three-toed), and could have been made by ''Dilophosaurus''; Welles created the new ichnogenus and species ''Dilophosauripus williamsi'' based on them, in honor of Williams, the discoverer of the first ''Dilophosaurus'' skeletons. The type specimen is a cast of a large footprint catalogued as UCMP 79690-4, with casts of three other prints included in the hypodigm. In 1984, Welles conceded that no way had been found to prove or disprove that the footprints belonged to ''Dilophosaurus''. In 1996, the paleontologists Michael Morales and Scott Bulkey reported a trackway of the ichnogenus '' Eubrontes'' from the Kayenta Formation made by a very large theropod. They noted it could have been made by a very large ''Dilophosaurus'' individual, but found that unlikely, as they estimated the trackmaker would have been tall at the hips, compared to the of ''Dilophosaurus''. The paleontologist Gerard Gierliński examined tridactyl footprints from the Holy Cross Mountains in Poland and concluded in 1991 that they belonged to a theropod like ''Dilophosaurus''. He named the new ichnospecies '' Grallator'' (''Eubrontes'') ''soltykovensis'' based on them, with a cast of footprint MGIW 1560.11.12 as the holotype. In 1994 Gierliński also assigned footprints from the
Höganäs Formation The Höganäs Formation is a Late Triassic to Early Jurassic geologic Formation (geology), formation in Skåne, Sweden. The formation is mostly known for its incredible flora collection from the Bjuv member, composed of over 110 species, and also ...
in Sweden discovered in 1974 to ''G. (E.) soltykovensis''. In 1996, Gierliński attributed track AC 1/7 from the
Turners Falls Formation The Turners Falls Formation or Turners Falls Sandstone is an Early Jurassic geological formation in Massachusetts. Various reptile tracks and footprints are known from this strata. These include '' Antipus flexiloquus'', which has been interprete ...
of Massachusetts, a resting trace he believed to show feather impressions, to a theropod similar to ''Dilophosaurus'' and ''Liliensternus'', and assigned it to the ichnotaxon ''Grallator minisculus''. The paleontologist Martin Kundrát agreed that the track showed feather impressions in 2004, but this interpretation was disputed by the paleontologist
Martin Lockley Martin G. Lockley (born 1950) is a Welsh palaeontologist. He was educated in the United Kingdom where he obtained degrees (BSc and PhD) and post-doctoral experience in Geology in the 1970s. Since 1980 he has been a professor at the Universit ...
and colleagues in 2003 and the paleontologist
Anthony J. Martin Anthony J. Martin is a paleontologist who has taught at Emory University since the early 1990s. He is best known for his books, ''An Introduction to the Study of Dinosaurs'', ''Life Traces of the Georgia Coast'', ''Dinosaurs without Bones'', and ' ...
and colleagues in 2004, who considered them as sedimentological artifacts. Martin and colleagues also reassigned the track to the ichnotaxon '' Fulicopus lyellii''. Gierliński and Karol Sabath responded at a conference talk in 2005, pointing out that the algae mat imprint would not only have been present on the stomach, but also the footprints. Based on detailed photos and experiments, they found the traces similar to those left by the fibrous feathers (semiplumes) of modern birds, and different from those left by a scaly body. The paleontologist Robert E. Weems proposed in 2003 that ''Eubrontes'' tracks were not produced by a theropod, but by a sauropodomorph similar to '' Plateosaurus'', excluding ''Dilophosaurus'' as a possible trackmaker. Instead, Weems proposed '' Kayentapus hopii'', another ichnotaxon named by Welles in 1971, as the best match for ''Dilophosaurus''. The attribution to ''Dilophosaurus'' was primarily based on the wide angle between digit impressions three and four shown by these tracks, and the observation that the foot of the holotype specimen shows a similarly splayed-out fourth digit. Also in 2003, paleontologist Emma Rainforth argued that the splay in the holotype foot was merely the result of distortion, and that ''Eubrontes'' would indeed be a good match for ''Dilophosaurus''. The paleontologist
Spencer G. Lucas Spencer George Lucas is an American paleontologist and stratigrapher, and curator of paleontology at the New Mexico Museum of Natural History and Science. His main areas of study are late Paleozoic, Mesozoic and early Cenozoic vertebrate fossils ...
and colleagues stated in 2006 that virtually universal agreement existed that ''Eubrontes'' tracks were made by a theropod like ''Dilophosaurus'', and that they and other researchers dismissed Weems' claims. In 2006, Weems defended his 2003 assessment of ''Eubrontes'', and proposed an animal like ''Dilophosaurus'' as the possible trackmaker of numerous ''Kayentapus'' trackways of the Culpeper Quarry in Virginia. Weems suggested rounded impressions associated with some of these trackways to represent hand impressions lacking digit traces, which he interpreted as a trace of quadrupedal movement. Milner and colleagues used the
new combination ''Combinatio nova'', abbreviated ''comb. nov.'' (sometimes ''n. comb.''), is Latin for "new combination". It is used in taxonomic biology literature when a new name is introduced based on a pre-existing name. The term should not to be confused wi ...
''Kayentapus soltykovensis'' in 2009, and suggested that ''Dilophosauripus'' may not be distinct from ''Eubrontes'' and ''Kayentapus''. They suggested that the long claw marks that were used to distinguish ''Dilophosauripus'' may be an artifact of dragging. They found that ''Gigandipus'' and ''Anchisauripus'' tracks may likewise also just represent variations of ''Eubrontes''. They pointed out that differences between ichnotaxa may reflect how the trackmaker interacted with the substrate rather than taxonomy. They also found ''Dilophosaurus'' to be a suitable match for a ''Eubrontes'' trackway and resting trace (SGDS 18.T1) from the St. George dinosaur discovery site in the Moenave Formation of Utah, though the dinosaur itself is not known from the formation, which is slightly older than the Kayenta Formation. Weems stated in 2019 that ''Eubrontes'' tracks do not reflect the gracile feet of ''Dilophosaurus'', and argued they were instead made by the bipedal sauropodopormph '' Anchisaurus''.


Paleobiology


Feeding and diet

Welles found that ''Dilophosaurus'' did not have a powerful bite, due to weakness caused by the subnarial gap. He thought that it used its front premaxillary teeth for plucking and tearing rather than biting, and the maxillary teeth further back for piercing and slicing. He thought that it was probably a scavenger rather than a predator, and that if it did kill large animals, it would have done so with its hands and feet rather than its jaws. Welles did not find evidence of cranial kinesis in the skull of ''Dilophosaurus'', a feature that allows individual bones of the skull to move in relation to each other. In 1986, the paleontologist
Robert T. Bakker Robert Thomas Bakker (born March 24, 1945) is an American paleontologist who helped reshape modern theories about dinosaurs, particularly by adding support to the theory that some dinosaurs were endothermic (warm-blooded). Along with his mentor J ...
instead found ''Dilophosaurus'', with its massive neck and skull and large upper teeth, to have been adapted for killing large prey, and strong enough to attack any Early Jurassic herbivores. In 1988, Paul dismissed the idea that ''Dilophosaurus'' was a scavenger, and claimed that strictly scavenging terrestrial animals are a myth. He stated that the snout of ''Dilophosaurus'' was better braced than had been thought previously, and that the very large, slender maxillary teeth were more lethal than the claws. Paul suggested that it hunted large animals such as prosauropods, and that it was more capable of snapping small animals than other theropods of a similar size. A 2005 beam-theory study by the palaeontologist François Therrien and colleagues found that the bite force in the mandible of ''Dilophosaurus'' decreased rapidly hindwards in the tooth-throw. This indicates that the front of the mandible, with its upturned chin, " rosette" of teeth, and strengthened symphysal region (similar to spinosaurids), was used to capture and manipulate prey, probably of relatively smaller size. The properties of its mandibular symphysis were similar to those of felids and crocodilians that use the front of their jaws to deliver a powerful bite when subduing prey. The loads exerted on the mandibles were consistent with struggle of small prey, which may have been hunted by delivering slashing bites to wound it, and then captured with the front of the jaws after being too weakened to resist. The prey may then have been moved further back into the jaws, where the largest teeth were located, and killed by slicing bites (similar to some crocodilians) with the sideways-compressed teeth. The authors suggested that if ''Dilophosaurus'' indeed fed on small prey, possible hunting packs would have been of limited size. Milner and paleontologist
James I. Kirkland James Ian Kirkland (born August 24, 1954) is an American paleontologist and geologist. He has worked with dinosaur remains from the south west United States of America and Mexico and has been responsible for discovering new and important genera. ...
suggested in 2007 that ''Dilophosaurus'' had features that indicate it may have eaten fish. They pointed out that the ends of the jaws were expanded to the sides, forming a "rosette" of interlocking teeth, similar to those of spinosaurids, known to have eaten fish, and
gharials Gavialidae is a family of large semiaquatic crocodilians with elongated, narrow snouts. Gavialidae consists of two living species, the gharial (''Gavialis gangeticus'') and the false gharial (''Tomistoma schlegelii''), both occurring in Asia. Man ...
, which is the modern
crocodile Crocodiles (family (biology), family Crocodylidae) or true crocodiles are large semiaquatic reptiles that live throughout the tropics in Africa, Asia, the Americas and Australia. The term crocodile is sometimes used even more loosely to inclu ...
that eats the most fish. The nasal openings were also retracted back on the jaws, similar to spinosaurids, which have even more retracted nasal openings, and this may have limited water splashing into the nostrils during fishing. Both groups also had long arms with well-developed claws, which could help when catching fish. Lake Dixie, a large lake that extended from Utah to Arizona and Nevada, would have provided abundant fish in the "post-cataclysmic", biologically more impoverished world that followed the Triassic–Jurassic extinction event (wherein about three quarters of life on Earth vanished), 5 to 15 million years before ''Dilophosaurus'' appeared. In 2018, Marsh and Rowe reported that the holotype specimen of the sauropodomorph '' Sarahsaurus'' bore possible tooth marks scattered across the skeleton that may have been left by ''Dilophosaurus'' (''Syntarsus'' was too small to have produced them) scavenging the specimen after it died (the positions of the bones may also have been disturbed by scavenging). An example of such marks can be seen on the left scapula, which has an oval depression on the surface of its upper side, and a large hole on the lower front end of the right tibia. The quarry where the holotype and paratype specimens of ''Sarahsaurus'' were excavated also contained a partial immature ''Dilophosaurus'' specimen. Marsh and Rowe suggested in 2020 that many of the features that distinguished ''Dilophosaurus'' from earlier theropods were associated with increased body size and macropredation (preying on large animals). While Marsh and Rowe agreed that ''Dilophosaurus'' could have fed on fish and small prey in the fluvial system in its environment, they pointed out that the articulation between the premaxilla and maxilla of the upper jaw was immobile and much more robust than previously thought, and that large-bodied prey could have been grasped and manipulated with the forelimbs during predation and scavenging. They considered the large bite marks on ''Sarahsaurus'' specimens alongside shed teeth and the presence of a ''Dilophosaurus'' specimen within the same quarry as support for this idea. In a 2021 article, paleontologist Matthew A. Brown and Rowe stated that these remains showed that ''Dilophosaurus'' had jaws strong enough to puncture bone. The fleshy air sacs from its respiratory system that grew into the vertebrae both strengthened and lightened the skeleton, and allowed unidirectional airflow through its lungs, similar to birds and crocodiles, and thereby more oxygen than a bidirectional respiratory system of mammals (wherein the air flows in and out of the lungs). Unidirectional breathing indicates relatively high metabolic rates and therefore high levels of activity, indicating that ''Dilophosaurus'' was likely a fast, agile hunter. Brown and Rowe considered ''Dilophosaurus'' to have been an apex predator in its ecosystem, and not a scavenger.


Motion

Welles envisioned ''Dilophosaurus'' as an active, clearly bipedal animal, similar to an enlarged ostrich. He found the forelimbs to have been powerful weapons, strong and flexible, and not used for locomotion. He noted that the hands were capable of grasping and slashing, of meeting each other, and reaching two-thirds up the neck. He proposed that in a sitting posture, the animal would rest on the large "foot" of its ischium, as well as its tail and feet. In 1990, paleontologists Stephen and Sylvia Czerkas suggested that the weak pelvis of ''Dilophosaurus'' could have been an adaptation for an aquatic lifestyle, where the water would help support its weight, and that it could have been an efficient swimmer. They found it doubtful that it would have been restricted to a watery environment, though, due to the strength and proportions of its hind limbs, which would have made it fleet-footed and agile during bipedal locomotion. Paul depicted ''Dilophosaurus'' bouncing on its tail while lashing out at an enemy, similar to a kangaroo. In 2005, paleontologists Phil Senter and James H. Robins examined the range of motion in the forelimbs of ''Dilophosaurus'' and other theropods. They found that ''Dilophosaurus'' would have been able to draw its humerus backward until it was almost parallel with the scapula, but could not move it forwards to a more than vertical orientation. The elbow could approach full extension and flexion at a right angle, but not achieve it completely. The fingers do not appear to have been voluntarily hyperextensible (able to extend backwards, beyond their normal range), but they may have been passively hyperextensible, to resist dislocation during violent movements by captured prey. A 2015 article by Senter and Robins gave recommendations for how to reconstruct the fore limb posture in bipedal dinosaurs, based on examination of various taxa, including ''Dilophosaurus''. The scapulae were held very horizontally, the resting orientation of the elbow would have been close to a right angle, and the orientation of the hand would not have deviated much from that of the lower arm. In 2018, Senter and Corwin Sullivan examined the range of motion in the fore limb joints of ''Dilophosaurus'' by manipulating the bones, to test hypothesized functions of the fore limbs. They also took into account that experiments with alligator carcasses show that the range of motion is greater in elbows covered in soft tissue (such as
cartilage Cartilage is a resilient and smooth type of connective tissue. In tetrapods, it covers and protects the ends of long bones at the joints as articular cartilage, and is a structural component of many body parts including the rib cage, the neck an ...
, ligaments, and muscles) than what would be indicated by manipulation of bare bones. They found that the humerus of ''Dilophosaurus'' could be retracted into a position that was almost parallel with the scapula, protracted to an almost vertical level, and elevated 65°. The elbow could not be flexed past a right angle to the humerus.
Pronation Motion, the process of movement, is described using specific anatomical terms. Motion includes movement of organs, joints, limbs, and specific sections of the body. The terminology used describes this motion according to its direction relative ...
and
supination Motion, the process of movement, is described using specific anatomical terms. Motion includes movement of organs, joints, limbs, and specific sections of the body. The terminology used describes this motion according to its direction relative ...
of the wrists (crossing the radius and ulna bones of the lower arm to turn the hand) was prevented by the radius and ulna joints not being able to roll, and the palms, therefore, faced medially, towards each other. The inability to pronate the wrists was an ancestral feature shared by theropods and other dinosaur groups. The wrist had limited mobility, and the fingers diverged during flexion, and were very hyperextensible. Senter and Sullivan concluded that ''Dilophosaurus'' was able to grip and hold objects between two hands, to grip and hold small objects in one hand, to seize objects close beneath the chest, to bring an object to the mouth, to perform a display by swinging the arms in an arc along the sides of the ribcage, to scratch the chest, belly, or the half of the other forelimb farthest from the body, to seize prey beneath the chest or the base of the neck, and to clutch objects to the chest. ''Dilophosaurus'' was unable to perform scratch-digging, hook-pulling, to hold objects between two fingertips of one hand, to maintain balance by extending the arms outwards to the sides, or to probe small crevices like the modern aye aye does. The hyperextensibility of the fingers may have prevented the prey's violent struggle from dislocating them, since it would have allowed greater motion of the fingers (with no importance to locomotion). The limited mobility of the shoulder and shortness of the forelimbs indicates that the mouth made first contact with the prey rather than the hands. Capture of prey with the forelimbs would only be possible for seizing animals small enough to fit beneath the chest of ''Dilophosaurus'', or larger prey that had been forced down with its mouth. The great length of the head and neck would have enabled the snout to extend much further than the hands. The ''Dilophosauripus'' footprints reported by Welles in 1971 were all on the same level, and were described as a "chicken yard hodge-podge" of footprints, with few forming a trackway. The footprints had been imprinted in mud, which allowed the feet to sink down . The prints were sloppy, and the varying breadth of the toe prints indicates that mud had clung to the feet. The impressions varied according to differences in the substrate and the manner in which they were made; sometimes, the foot was planted directly, but often a backward or forward slip occurred as the foot came down. The positions and angles of the toes also varied considerably, which indicate they must have been quite flexible. The ''Dilophosauripus'' footprints had an offset second toe with a thick base, and very long, straight claws that were in line with the axes of the toe pads. One of the footprints was missing the claw of the second toe, perhaps due to injury. In 1984, Welles interpreted the fact that three individuals were found close together, and the presence of criss-crossed trackways nearby, as indications that ''Dilophosaurus'' traveled in groups. Gay agreed that they may have traveled in small groups, but noted that no direct evidence supported this, and that flash floods could have picked up scattered bones from different individuals and deposited them together. Milner and colleagues examined the possible ''Dilophosaurus'' trackway SGDS 18.T1 in 2009, which consists of typical footprints with tail drags and a more unusual resting trace, deposited in lacustrine beach sandstone. The trackway began with the animal first oriented approximately in parallel with the shoreline, and then stopping by a berm with both feet in parallel, whereafter it lowered its body, and brought its metatarsals and the
callosity A callosity is another name for callus, a piece of skin that has become thickened as a result of repeated contact and friction. Primates All Old World monkeys, gibbons, and some chimpanzees have pads on their rears known as ischial callositie ...
around its ischium to the ground; this created impressions of symmetrical "heels" and circular impressions of the ischium. The part of the tail closest to the body was kept off the ground, whereas the end further away from the body made contact with the ground. The fact that the animal rested on a slope is what enabled it to bring both hands to the ground close to the feet. After resting, the dinosaur shuffled forwards, and left new impressions with its feet, metatarsals, and ischium, but not the hands. The right foot now stepped on the print of the right hand, and the second claw of the left foot made a drag mark from the first resting position to the next. After some time, the animal stood up and moved forwards, with the left foot first, and once fully erect, it walked across the rest of the exposed surface, while leaving thin drag marks with the end of the tail. Crouching is a rarely captured behavior of theropods, and SGDS 18.T1 is the only such track with unambiguous impressions of theropod hands, which provides valuable information about how they used their forelimbs. The crouching posture was found to be very similar to that of modern birds, and shows that early theropods held the palms of their hands facing medially, towards each other. As such a posture therefore evolved early in the lineage, it may have characterized all theropods. Theropods are often depicted with their palms facing downwards, but studies of their functional anatomy have shown that they, like birds, were unable to pronate or supinate their arms. The track showed that the legs were held symmetrically with the body weight distributed between the feet and the metatarsals, which is also a feature seen in birds such as ratites. Milner and colleagues also dismissed the idea that the ''Kayentapus minor'' track reported by Weems showed a palm imprint made by a quadrupedally walking theropod. Weems had proposed the trackmaker would have been able to move quadrupedally when walking slowly, while the digits would have been habitually hyperextended so only the palms touched the ground. Milner and colleagues found the inferred pose unnecessary, and suggested the track was instead made in a similar way as SGDS 18.T1, but without leaving traces of the digits.


Crest function

Welles conceded that suggestions as to the function of the crests of ''Dilophosaurus'' were conjectural, but thought that, though the crests had no grooves to indicate vascularization, they could have been used for thermoregulation. He also suggested they could have been used for
species recognition Intra-species recognition is the recognition by a member of a species of a conspecific (another member of the same species). In many species, such recognition is necessary for procreation. Different species may employ different methods, but all ...
or
ornamentation An ornament is something used for decoration. Ornament may also refer to: Decoration *Ornament (art), any purely decorative element in architecture and the decorative arts *Biological ornament, a characteristic of animals that appear to serve on ...
. The Czerkas pointed out that the crests could not have been used during battle, as their delicate structure would have been easily damaged. They suggested that they were a visual display for attracting a mate, and even thermoregulation. In 1990, paleontologist Walter P. Coombs stated that the crests may have been enhanced by colors for use in display. In 2011 the paleontologists Kevin Padian and
John R. Horner John is a common English name and surname: * John (given name) * John (surname) John may also refer to: New Testament Works * Gospel of John, a title often shortened to John * First Epistle of John, often shortened to 1 John * Second E ...
proposed that "bizarre structures" in dinosaurs in general (including crests, frills, horns, and domes) were primarily used for species recognition, and dismissed other explanations as unsupported by evidence. They noted that too few specimens of cranially ornamented theropods, including ''Dilophosaurus'', were known to test their evolutionary function statistically, and whether they represented sexual dimorphism or sexual maturity. In a response to Padian and Horner the same year, the paleontologists Rob J. Knell and
Scott D. Sampson Scott Donald Sampson (born April 22, 1961) is a Canadian paleontologist and science communicator. Sampson is currently the Executive Director of California Academy of Sciences in San Francisco, California. He was previously Vice President of Res ...
argued that species recognition was not unlikely as a secondary function for "bizarre structures" in dinosaurs, but that sexual selection (used in display or combat to compete for mates) was a more likely explanation, due to the high cost of developing them, and because such structures appear to be highly variable within species. In 2013, paleontologists David E. Hone and Darren Naish criticized the "species recognition hypothesis", and argued that no extant animals use such structures primarily for species recognition, and that Padian and Horner had ignored the possibility of mutual sexual selection (where both sexes are ornamented). Marsh and Rowe agreed in 2020 that the crests of ''Dilophosaurus'' likely had a role in species identification or intersexual/intrasexual selection, as in some modern birds. It is unknown if the air sacs in the crests supported such functions.


Development

Welles originally interpreted the smaller ''Dilophosaurus'' specimens as juveniles, and the larger specimen as an adult, later interpreting them as different species. Paul suggested that the differences between the specimens was perhaps due to sexual dimorphism, as was seemingly also apparent in ''Coelophysis'', which had "robust" and "gracile" forms of the same size, that might otherwise have been regarded as separate species. Following this scheme, the smaller ''Dilophosaurus'' specimen would represent a "gracile" example. In 2005 Tykoski found that most ''Dilophosaurus'' specimens known were juvenile individuals, with only the largest an adult, based on the level of co-ossification of the bones. In 2005 Gay found no evidence of the sexual dimorphism suggested by Paul (but supposedly present in ''Coelophysis''), and attributed the variation seen between ''Dilophosaurus'' specimens to individual variation and ontogeny (changes during growth). There was no dimorphism in the skeletons, but he did not rule out that there could have been in the crests; more data was needed to determine this. Based on the tiny nasal crests on a juvenile specimen, Yates had tentatively assigned to the related genus ''Dracovenator'', he suggested that these would have grown larger as the animal became adult. The paleontologist J.S. Tkach reported a histological study (microscopical study of internal features) of ''Dilophosaurus'' in 1996, conducted by taking
thin-sections In optical mineralogy and petrography, a thin section (or petrographic thin section) is a thin slice of a rock or mineral sample, prepared in a laboratory, for use with a polarizing petrographic microscope, electron microscope and electron mic ...
of long bones and ribs of specimen UCMP 37303 (the lesser preserved of the two original skeletons). The bone tissues were well vascularized and had a fibro-lamellar structure similar to that found in other theropods and the sauropodomorph '' Massospondylus''. The plexiform (woven) structure of the bones suggested rapid growth, and ''Dilophosaurus'' may have attained a growth rate of per year early in life. Welles found that the replacement teeth of ''Dilophosaurus'' and other theropods originated deep inside the bone, decreasing in size the farther they were from the alveolar border. There were usually two or three replacement teeth in the alveoli, with the youngest being a small, hollow crown. The replacement teeth erupted on the outer side of the old teeth. When a tooth neared the
gum line The gums or gingiva (plural: ''gingivae'') consist of the mucosal tissue that lies over the mandible and maxilla inside the mouth. Gum health and disease can have an effect on general health. Structure The gums are part of the soft tissue linin ...
, the inner wall between the interdental plates was resorbed and formed a nutrient notch. As the new tooth erupted, it moved outwards to center itself in the alveolus, and the nutrient notch closed over.


Paleopathology

Welles noted various paleopathologies (ancient signs of disease, such as injuries and malformations) in ''Dilophosaurus''. The holotype had a sulcus (groove or furrow) on the neural arch of a cervical vertebra that may have been due to an injury or crushing, and two pits on the right humerus that may have been abscesses (collections of
pus Pus is an exudate, typically white-yellow, yellow, or yellow-brown, formed at the site of inflammation during bacterial or fungal infection. An accumulation of pus in an enclosed tissue space is known as an abscess, whereas a visible collection ...
) or artifacts. Welles also noted that it had a smaller and more delicate left humerus than the right, but with the reverse condition in its forearms. In 2001, paleontologist Ralph Molnar suggested that this was caused by a developmental anomaly called
fluctuating asymmetry Fluctuating asymmetry (FA), is a form of biological asymmetry, along with anti-symmetry and direction asymmetry. Fluctuating asymmetry refers to small, random deviations away from perfect bilateral symmetry. This deviation from perfection is thoug ...
. This anomaly can be caused by stress in animal populations, for example due to disturbances in their environment, and may indicate more intense selective pressure. Asymmetry can also result from traumatic events in early development of an animal, which would be more randomly distributed in time. A 2001 study conducted by paleontologist Bruce Rothschild and colleagues examined 60 ''Dilophosaurus'' foot bones for signs of stress fractures (which are caused by strenuous, repetitive actions), but none were found. Such injuries can be the result of very active, predatory lifestyles. In 2016 Senter and Sara L. Juengst examined the paleopathologies of the holotype specimen and found that it bore the greatest and most varied number of such maladies on the pectoral girdle and forelimb of any theropod dinosaur so far described, some of which are not known from any other dinosaur. Only six other theropods are known with more than one paleopathology on the pectoral girdle and forelimbs. The holotype specimen had eight afflicted bones, whereas no other theropod specimen is known with more than four. On its left side, it had a fractured scapula and radius, and fibriscesses (like abscesses) in the ulna and the outer phalanx bone of the thumb. On the right side it had torsion of its humeral shaft, three bony tumors on its radius, a truncated articular surface of its third metacarpal bone, and deformities on the first phalanx bone of the third finger. This finger was permanently deformed and unable to flex. The deformities of the humerus and the third finger may have been due to
osteodysplasia Osteochondrodysplasia is a general term for a disorder of the development ( dysplasia) of bone ("osteo") and cartilage ("chondro"). Osteochondrodysplasias are rare diseases. About 1 in 5,000 babies are born with some type of skeletal dysplasia. N ...
, which had not been reported from non-avian dinosaurs before, but is known in birds. Affecting juvenile birds that have experienced malnutrition, this disease can cause pain in one limb, which makes the birds prefer to use the other limb instead, which thereby develops torsion. The number of traumatic events that led to these features is not certain, and it is possible that they were all caused by a single encounter, for example by crashing into a tree or rock during a fight with another animal, which may have caused puncture wounds with its claws. Since all the injuries had healed, it is certain that the ''Dilophosaurus'' survived for a long time after these events, for months, perhaps years. The use of the forelimbs for prey capture must have been compromised during the healing process. The dinosaur may therefore have endured a long period of fasting or subsisted on prey that was small enough for it to dispatch with the mouth and feet, or with one forelimb. According to Senter and Juengst, the high degree of pain the dinosaur might have experienced in multiple locations for long durations also shows that it was a hardy animal. They noted that paleopathologies in dinosaurs are underreported, and that even though Welles had thoroughly described the holotype, he had mentioned only one of the pathologies found by them. They suggested that such features may sometimes be omitted because descriptions of species are concerned with their characteristics rather than abnormalities, or because such features are difficult to recognize. Senter and Sullivan found that the pathologies significantly altered the range of motion in the right shoulder and right third finger of the holotype, and that estimates for range of motion may therefore not match those made for a healthy forelimb.


Paleoecology

''Dilophosaurus'' is known from the Kayenta Formation, which dates to the Sinemurian and Pliensbachian stages of the Early Jurassic, approximately 196–183 million years ago. The Kayenta Formation is part of the Glen Canyon Group that includes formations in northern Arizona, parts of southeastern Utah, western Colorado, and northwestern New Mexico. It is composed mostly of two
facies In geology, a facies ( , ; same pronunciation and spelling in the plural) is a body of rock with specified characteristics, which can be any observable attribute of rocks (such as their overall appearance, composition, or condition of formatio ...
, one dominated by
siltstone Siltstone, also known as aleurolite, is a clastic sedimentary rock that is composed mostly of silt. It is a form of mudrock with a low clay mineral content, which can be distinguished from shale by its lack of fissility.Blatt ''et al.'' 1980, p ...
deposition and the other by sandstone. The siltstone facies is found in much of Arizona, while the sandstone facies is present in areas of northern Arizona, southern Utah, western Colorado, and northwestern New Mexico. The formation was primarily deposited by rivers, with the siltstone facies as the slower, more sluggish part of the river system. Kayenta Formation deposition was ended by the encroaching dune field that would become the
Navajo Sandstone The Navajo Sandstone is a geological formation in the Glen Canyon Group that is spread across the U.S. states of southern Nevada, northern Arizona, northwest Colorado, and Utah as part of the Colorado Plateau province of the United States.Anonymou ...
. The environment was seasonally dry, with sand dunes migrating in and out of the wet environments where animals lived, and has been likened to a river
oasis In ecology, an oasis (; ) is a fertile area of a desert or semi-desert environment'ksar''with its surrounding feeding source, the palm grove, within a relational and circulatory nomadic system.” The location of oases has been of critical imp ...
; a waterway lined with
conifers Conifers are a group of cone-bearing seed plants, a subset of gymnosperms. Scientifically, they make up the division Pinophyta (), also known as Coniferophyta () or Coniferae. The division contains a single extant class, Pinopsida. All extan ...
and surrounded by sand. A definitive radiometric dating of this formation has not yet been made, and the available stratigraphic correlation has been based on a combination of radiometric dates from vertebrate fossils, magnetostratigraphy, and pollen evidence. ''Dilophosaurus'' appears to have survived for a considerable span of time, based on the position of the specimens within the Kayenta Formation. The Kayenta Formation has yielded a small but growing assemblage of organisms. Most fossils are from the siltstone facies. Most organisms known so far are vertebrates. Non-vertebrates include microbial or "algal" limestone, petrified wood, plant impressions, freshwater bivalves and snails, ostracods, and invertebrate trace fossils. Vertebrates are known from both body fossils and trace fossils. Vertebrates known from body fossils include hybodont sharks, indeterminate
bony fish Osteichthyes (), popularly referred to as the bony fish, is a diverse superclass of fish that have skeletons primarily composed of bone tissue. They can be contrasted with the Chondrichthyes, which have skeletons primarily composed of cartilag ...
, lungfish, salamanders, the frog ''
Prosalirus ''Prosalirus'' is the name given to a fossilised prehistoric frog found in the Kayenta Formation of Arizona in 1981 by Farish Jenkins.''Geographica''; "Jurassic Frog hops into the record book", National Geographic; August 1996, pg.5. The type, an ...
'', the
caecilia ''Caecilia'' is a genus of amphibians in the family Caeciliidae Caeciliidae is the family of common caecilians. They are found in Central and South America. Like other caecilians, they superficially resemble worms or snakes. Although they ...
n '' Eocaecilia'', the turtle ''
Kayentachelys ''Kayentachelys'' ("Kayenta turtle") is an extinct genus of turtle known only from the "silty facies" of the Lower Jurassic Kayenta Formation in northeastern Arizona on the lands of the Navajo Nation. History of discovery and significance The e ...
'', a sphenodontian reptile, lizards, and several early
crocodylomorphs Crocodylomorpha is a group of pseudosuchian archosaurs that includes the crocodilians and their extinct relatives. They were the only members of Pseudosuchia to survive the end-Triassic extinction. During Mesozoic and early Cenozoic times, cr ...
including '' Calsoyasuchus'', ''
Eopneumatosuchus ''Eopneumatosuchus'' is an extinct genus of basal crocodyliform. Fossils have been found from two localities within the Kayenta Formation of Arizona. Both localities are around 20 miles southeast of the Grand Canyon and in close proximity to on ...
'', ''
Kayentasuchus ''Kayentasuchus'' (meaning "Kayenta Formation crocodile") is a genus of sphenosuchian, a type of basal crocodylomorph, the clade that comprises the crocodilians and their closest kin. It is known from a single skeleton found in rocks of the Si ...
'', and ''
Protosuchus ''Protosuchus'' is an extinct genus of carnivorous crocodylomorph from the Early Jurassic. The name ''Protosuchus'' means "first crocodile", and is among the earliest animals that resemble crocodilians. ''Protosuchus'' was about in length and ...
'', and the pterosaur '' Rhamphinion''. Apart from ''Dilophosaurus'', several dinosaurs are known, including the theropods '' Megapnosaurus'', and ''
Kayentavenator ''Kayentavenator'' (meaning "Kayenta hunter") is a genus of small carnivorous tetanuran dinosaur that lived during the Early Jurassic Period; fossils were recovered from the Kayenta Formation of northeastern Arizona and were described in 2010.Ga ...
'', the sauropodomorph ''Sarahsaurus'', a
heterodontosaurid Heterodontosauridae is a family of ornithischian dinosaurs that were likely among the most basal (primitive) members of the group. Their phylogenetic placement is uncertain but they are most commonly found to be primitive, outside of the group ...
, and the
thyreophoran Thyreophora ("shield bearers", often known simply as "armored dinosaurs") is a group of armored ornithischian dinosaurs that lived from the Early Jurassic until the end of the Cretaceous. Thyreophorans are characterized by the presence of body ...
'' Scutellosaurus''.
Synapsids Synapsids + (, 'arch') > () "having a fused arch"; synonymous with ''theropsids'' (Greek, "beast-face") are one of the two major groups of animals that evolved from basal amniotes, the other being the Sauropsida, sauropsids, the group that inc ...
include the
tritylodontids Tritylodontidae ("three-knob teeth", named after the shape of their cheek teeth) is an extinct family of small to medium-sized, highly specialized mammal-like cynodonts, bearing several mammalian traits like erect limbs, endothermy and details ...
''
Dinnebitodon ''Dinnebitodon'' is an extinct genus of advanced herbivorous cynodonts of the early Jurassic period. It has only been found in the Kayenta Formation in northeastern Arizona. It closely resembles the related genus ''Kayentatherium'' from the sa ...
'', '' Kayentatherium'', and '' Oligokyphus'', morganucodontids, the possible early true mammal ''
Dinnetherium ''Dinnetherium'' is an extinct genus of morganucodont mammaliaform that is part of the monotypic order Dinnetheria and is also part of the monotypic family Dinnetheriidae.A. O. Averianov and A. V. Lopatin. 2011. Phylogeny of Triconodonts and Symm ...
'', and a
haramiyid Haramiyida ("thief" from Arabic الحرامية (al ḥarāmiyah), "thief, bandit") is a possibly polyphyletic order of mammaliaform cynodonts or mammals of controversial taxonomic affinites. Their teeth, which are by far the most common remai ...
mammal. The majority of these finds come from the vicinity of Gold Spring, Arizona. Vertebrate trace fossils include coprolites and the tracks of therapsids, lizard-like animals, and several types of dinosaur.


Taphonomy

Welles outlined the taphonomy of the original specimens, changes that happened during their decay and fossilization. The holotype skeleton was found lying on its right side, and its head and neck were recurvedcurved backwardsin the "
death pose Non-avian dinosaur and bird fossils are frequently found in a characteristic posture consisting of head thrown back, tail extended, and mouth wide open. The cause of this posture—often called a "death pose"—has been a matter of scientific deba ...
" in which dinosaur skeletons are often found. This pose was thought to be
opisthotonus Opisthotonus or opisthotonos (from grc, ὄπισθεν, translit=opisthen, lit=behind and grc, τόνος, translit=tonos, lit=tension, label=none) is a state of severe hyperextension and spasticity in which an individual's head, neck and spinal ...
(due to death-spasms) at the time, but may instead have been the result of how a carcass was embedded in sediments. The back was straight, and the hindmost dorsal vertebrae were turned on their left sides. The caudal vertebrae extended irregularly from the pelvis, and the legs were articulated, with little displacement. Welles concluded that the specimens were buried at the place of their deaths, without having been transported much, but that the holotype specimen appears to have been disturbed by scavengers, indicated by the rotated dorsal vertebrae and crushed skull. Gay noted that the specimens he described in 2001 showed evidence of having been transported by a stream. As none of the specimens were complete, they may have been transported over some distance, or have lain on the surface and weathered for some time before transport. They may have been transported by a flood, as indicated by the variety of animals found as fragments and bone breakage.


Cultural significance


''Jurassic Park''

''Dilophosaurus'' was featured in the 1990 novel ''
Jurassic Park ''Jurassic Park'', later also referred to as ''Jurassic World'', is an American science fiction media franchise created by Michael Crichton and centered on a disastrous attempt to create a theme park of cloned dinosaurs. It began in 1990 when ...
'', by the writer
Michael Crichton John Michael Crichton (; October 23, 1942 – November 4, 2008) was an American author and filmmaker. His books have sold over 200 million copies worldwide, and over a dozen have been adapted into films. His literary works heavily feature tech ...
, and its 1993
movie adaptation A film adaptation is the transfer of a work or story, in whole or in part, to a feature film. Although often considered a type of derivative work, film adaptation has been conceptualized recently by academic scholars such as Robert Stam as a dia ...
by the director
Steven Spielberg Steven Allan Spielberg (; born December 18, 1946) is an American director, writer, and producer. A major figure of the New Hollywood era and pioneer of the modern blockbuster, he is the most commercially successful director of all time. Spie ...
. The ''Dilophosaurus'' of ''
Jurassic Park ''Jurassic Park'', later also referred to as ''Jurassic World'', is an American science fiction media franchise created by Michael Crichton and centered on a disastrous attempt to create a theme park of cloned dinosaurs. It began in 1990 when ...
'' was acknowledged as the "only serious departure from scientific veracity" in the movie's making-of book, and as the "most fictionalized" of the movie's dinosaurs in a book about
Stan Winston Studios Stanley Winston (April 7, 1946 – June 15, 2008) was an American television and film Prosthetic makeup, special make-up effects creator, best known for his work in the Terminator (franchise), ''Terminator'' series, the first three ''Jurassic Pa ...
, which created the
animatronics Animatronics refers to mechatronic puppets. They are a modern variant of the automaton and are often used for the portrayal of characters in films and in theme park attractions. It is a multidisciplinary field integrating puppetry, anatomy a ...
effects. For the novel, Crichton invented the dinosaur's ability to spit venom (explaining how it was able to kill prey, in spite of its seemingly weak jaws). The art department added another feature, a neck frill or cowl folded against its neck that expanded and vibrated as the animal prepared to attack, similar to that of the frill-necked lizard. To avoid confusion with the '' Velociraptor'' as featured in the movie, ''Dilophosaurus'' was presented as only tall, instead of its assumed true height of about . Nicknamed "the spitter", the ''Dilophosaurus'' of the movie was realized through puppeteering, and required a full body with three interchangeable heads to produce the actions required by the script. Separate legs were also constructed for a shot where the dinosaur hops by. Unlike most of the other dinosaurs in the movie, no
computer-generated imagery Computer-generated imagery (CGI) is the use of computer graphics to create or contribute to images in art, printed media, video games, simulators, and visual effects in films, television programs, shorts, commercials, and videos. The images may ...
was employed when showing the ''Dilophosaurus''. The geologist J. Bret Bennington noted in 1996 that though ''Dilophosaurus'' probably did not have a frill and could not spit venom like in the movie, its bite could have been venomous, as has been claimed for the Komodo dragon. He found that adding venom to the dinosaur was no less allowable than giving a color to its skin, which is also unknown. If the dinosaur had a frill, there would have been evidence for this in the bones, in the shape of a rigid structure to hold up the frill, or markings at the places where the muscles used to move it were attached. He also added that if it did have a frill, it would not have used it to intimidate its meal, but rather a competitor (he speculated it may have responded to a character in the movie pulling a hood over his head). In a 1997 review of a book about the science of ''Jurassic Park'', the paleontologist Peter Dodson likewise pointed out the wrong scale of the film's ''Dilophosaurus'', as well as the improbability of its venom and frill. Bakker pointed out in 2014 that the movie's ''Dilophosaurus'' lacked the prominent notch in the upper jaw, and concluded that the movie-makers had done a good job at creating a frightening
chimaera Chimaeras are cartilaginous fish in the order Chimaeriformes , known informally as ghost sharks, rat fish, spookfish, or rabbit fish; the last three names are not to be confused with rattails, Opisthoproctidae, or Siganidae, respectively. At ...
of different animals, but warned it could not be used to teach about the real animal. Brown and Marsh stated that while these traits were fictitious, they were made believable by being based on the biology of real animals. Welles himself was "thrilled" to see ''Dilophosaurus'' in ''Jurassic Park'': he noted the inaccuracies, but found them minor points, enjoyed the movie, and was happy to find the dinosaur "an internationally known actor".


Attributed tracks

According to
Navajo myth The Navajo (; British English: Navaho; nv, Diné or ') are a Native Americans in the United States, Native American people of the Southwestern United States. With more than 399,494 enrolled tribal members , the Navajo Nation is the largest fe ...
, the carcasses of slain monsters were "beaten into the earth", but were impossible to obliterate, and fossils have traditionally been interpreted as their remains. While Navajo people have helped paleontologists locate fossils since the 19th century, traditional beliefs suggest that the ghosts of the monsters remain in their partially buried corpses, and have to be kept there through potent rituals. Likewise, some worry that the bones of their relatives would be dug up along with dinosaur remains, and that removing fossils shows disrespect to the past lives of these beings. In 2005, the historian Adrienne Mayor stated Welles had noted that during the original excavation of ''Dilophosaurus'', the Navajo Williams disappeared from the excavation after some days, and speculated this was because Williams found the detailed work with fine brushes "beneath his dignity". Mayor instead pointed out that Navajo men do occupy themselves with detailed work, such as jewellery and painting, and that the explanation for Williams' departure may instead have been traditional anxiety as the skeletons emerged and were disturbed. Mayor also pointed to an incident in the 1940s when a Navajo man helped excavate a '' Pentaceratops'' skeleton as long as he did not have to touch the bones, but left the site when only a few inches of dirt were left covering them. In a 1994 book, Welles said Williams had come back some days later with two Navajo women saying "that's no man's work, that's squaw's work". The cliffs in Arizona that contained the bones of ''Dilophosaurus'' also have petroglyphs by
ancestral Puebloans The Ancestral Puebloans, also known as the Anasazi, were an ancient Native American culture that spanned the present-day Four Corners region of the United States, comprising southeastern Utah, northeastern Arizona, northwestern New Mexico, a ...
carved onto them, and the criss-crossing tracks of the area are called ''Naasho’illbahitsho Biikee'' by the Navajo, meaning "big lizard tracks". According to Mayor, Navajos used to hold ceremonies and make offerings to these monster tracks. Tridactyl tracks were also featured as decorations on the costumes and
rock art In archaeology, rock art is human-made markings placed on natural surfaces, typically vertical stone surfaces. A high proportion of surviving historic and prehistoric rock art is found in caves or partly enclosed rock shelters; this type also ...
of the
Hopi The Hopi are a Native American ethnic group who primarily live on the Hopi Reservation in northeastern Arizona, United States. As of the 2010 census, there are 19,338 Hopi in the country. The Hopi Tribe is a sovereign nation within the Unite ...
and Zuni, probably influenced by such dinosaur tracks. In 2017 ''Dilophosaurus'' was designated as the
state dinosaur State may refer to: Arts, entertainment, and media Literature * '' State Magazine'', a monthly magazine published by the U.S. Department of State * ''The State'' (newspaper), a daily newspaper in Columbia, South Carolina, United States * ''Our ...
of the US state of Connecticut, to become official with the new state budget in 2019. ''Dilophosaurus'' was chosen because tracks thought to have been made by similar dinosaurs were discovered in Rocky Hill in 1966, during excavation for the
Interstate Highway 91 Interstate 91 (I-91) is an Interstate Highway System, Interstate Highway in the New England region of the United States. It provides the primary north–south thoroughfare in the western part of the region. The Interstate generally follows ...
. The six tracks were assigned to the ichnospecies ''Eubrontes giganteus'', which was made the
state fossil Most American states have made a state fossil designation, in many cases during the 1980s. It is common to designate one species in which fossilization has occurred, rather than a single specimen, or a category of fossils not limited to a single ...
of Connecticut in 1991. The area they were found in had been a Triassic lake, and when the significance of the area was confirmed, the highway was rerouted, and the area made a
state park State parks are parks or other protected areas managed at the sub-national level within those nations which use "state" as a political subdivision. State parks are typically established by a state to preserve a location on account of its natural ...
named Dinosaur State Park. In 1981 a sculpture of ''Dilophosaurus'', the first life-sized reconstruction of this dinosaur, was donated to the park. ''Dilophosaurus'' was proposed as the state dinosaur of Arizona by a 9-year-old boy in 1998, but lawmakers suggested ''
Sonorasaurus ''Sonorasaurus'' is a genus of Brachiosauridae, brachiosaurid dinosaur from the Early to Late Cretaceous (Albian to Cenomanian faunal stage, stages, around 112 to 93 Mya (unit), million years ago). It was a Herbivore, herbivorous sauropod wh ...
'' instead, arguing that ''Dilophosaurus'' was not unique to Arizona. A compromise was suggested that would recognize both dinosaurs, but the bill died when it was revealed that the ''Dilophosaurus'' fossils had been taken without permission from the Navajo Reservation, and because they did not reside in Arizona anymore (an 11-year-old boy again suggested ''Sonorasaurus'' as Arizona's state dinosaur in 2018). Navajo Nation officials subsequently discussed how to get the fossils returned. According to Mayor, one Navajo stated that they do not ask to get the fossils back anymore, but wondered why casts had not been made so the bones could be left, as it would be better to keep them in the ground, and a museum built so people could come to see them there. Further field work related to ''Dilophosaurus'' in the Navajo Nation was conducted with permission from the Navajo Nation Minerals Department.


References


External links

* {{Portal bar, Dinosaurs, United States Prehistoric neotheropods Early Jurassic genus first appearances Early Jurassic genus extinctions Early Jurassic dinosaurs of North America Fossils of the United States Kayenta Formation Fossil taxa described in 1970 Taxa named by Samuel Paul Welles