Paleo Profiles: Dilophosaurus

The reconstructed holotype at the Royal Ontario Museum

One of the most iconic dinosaurs from Jurassic Park is the crested Dilophosaurus which blinded and ate the hapless Dennis Nedry in one of the most iconic scenes of the movie. The Jurassic Park version of the Dilophosaurus has gone on to inspire recreations of the dinosaur in popular media, ranging from toys to video games. However, the real Dilophosaurus was fairly different from its Hollywood counterpart.

Discovery and Fossils

The Dilophosaurus was first discovered in 1942 by American palaeontologist Charles Camp, who was on an expedition to find vertebrate fossils in northern Arizona. In the Kayenta Formation, guided by local Navajo, the expedition found three dinosaur skeletons. While two were very eroded, the first one they found was almost complete. As always with fossils, there was a large gap in time between initial discovery and description, and the dinosaur was not named until 1954 by palaeontologist Samuel P. Welles. However, he believed that the new dinosaur was a species of an already discovered dinosaur called Megalosaurus, which was actually the first discovered/named dinosaur. Welles named the fossil Megalosaurus wetherelli after a Navajo councillor whose nephew had help discover the fossil, and who had helped the expedition himself. Megalosaurus has been seen as a 'wastebasket taxon' - a taxon where organisms don't seem to fit anywhere else are put in there. In 1964 Welles returned to the Kayenta Formation to find more fossils, and he found another near complete skeleton where the three earlier ones had found. What he found made him realise that Megalosaurus wetherelli was not as they initially thought. The skull of the new discovery had crests, and the dinosaur was overall larger than the earlier finds. Upon re-examining the holotype Welles realised that the crests had become dislodged from the skull, so he had the dinosaur renamed to Dilophosaurus wetherelli - 'Two-crested Lizard'. New fossils were found and in 1987 a near complete skeleton was discovered in Lufeng Province, China, and a few years later named Dilophosaurus sinensis. It was later discovered to not be actually a Dilophosaurus, but instead another species of a different dinosaur called Sinosaurus in 2017.

Biology

The real life Dilophosaurus differed greatly from its appearance in Jurassic Park

Dilophosaurus was a theropod dinosaur - this was a suborder of dinosaurs characterised by bipedal stances. This order includes many different species ranging from modern birds to the Tyrannosaurus. Existing at the very start of the Jurassic Period Dilophosaurus this means that it was one of the earliest theropods, and definitely one of the earliest large carnivores. When it was alive it would have been one of the largest carnivorous dinosaurs on the planet; from snout to tail it could reach 6 metres long, and could reach heights of up to 2 metres. Very different from the diminutive version in the movies. The initial three skeletons found were determined to be juveniles as the fossil found by Welles was much larger than the first three. An adult would therefore be the size of a brown bear. Just like a bear Dilophosaurus had very powerful arms - this will become important later. They were likely quite hardy animals. Phil Senter and Sara Juengst in 2016 found that one specimen had eight fairly bad injuries. However, most of the injuries showed signs of healing indicating that it could have lived years after getting initially wounded. A reason why it might have survived so long is possible evidence of pack behaviour. As specimens of similar ages have been found together it has led to the suggestion that they worked and lived together to survive - it would explain how the injured one lived. However, we cannot be entirely certain - a flash flood could explain why they were found together, especially considering how well preserved some specimens are. We now know that most dinosaurs would be feathered by the end of the Jurassic, but palaeontologists have been debating about when feathers developed. We have yet to find evidence of feathers on Dilophosaurus itself, but in 2004 Martin Kundrat reported finding traces of filaments from downy feathers on a theropod dinosaur from early Jurassic Massachusetts. If this dinosaur had some form of feathers it is not out of the question that Dilophosaurus also did so. Senter and Juengst even found that their specimen had a deformed humerus and finger thanks to developmental osteodysplasia - a condition previously only found in modern birds. If a Dilophosaurus has been found with this condition, this indicates that it more than likely had feathering.

A skull in the Royal Tyrell Museum

The most iconic part of Dilophosaurus is easily its crest. Unlike in Jurassic Park, the Dilophosaurus never had a frill - that was made up for the film, likely so audiences would not get it confused with the Velociraptors. The v-shaped crest shaped have often been disarticulated from the skull so for a while palaeontologists were not sure how it would go on the animal's head. Quite possibly the initial three specimens had their crests preserved, but as the expedition team did not know they existed consequently did not look for them. Initial reconstructions had the crest resting on the back of the skull and going onto the neck; this has since been rejected as it would restrict the neck's movement. Instead the crest started at the front of the skull and ended at the back. A real life equivalent could be the crest of a male cassowary, as shown below:

What were the crests used for? Initial theories of combat or thermoregulation have been rejected, so visual display is a likely function. Theropod dinosaurs likely could see bright colours as modern birds do, so the crests would be brightly coloured. Male Dilophosaurus would have the brightest crests in order to attract a mate, or scare off rival males. Finally, we have the jaw, which features a large notch in the upper jaw. This made it very weak - Dilophosaurus would be unable to break through bone. This led to questions about how or what it could eat - when writing Jurassic Park Michael Crichton theorised that they were venomous. We have no evidence for this, but palaeontologists have theorised how and what it ate.

Diet 

One of the biggest questions concerning the Dilophosaurus is its diet. With a weak jaw hunting down prey like a modern lion or wolf could be potentially dangerous. One wrong bite and its jaw would be broken. Different theories about how Dilophosaurus could have eaten. For one, it had very strong arms. Long, powerful arms, like a bear, could be used instead of its jaws to attack prey, and potential pack behaviour could improve the chances of a successful kill. One swipe could do serious damage, and an injured animal would be unable to escape when surrounded by other dinosaurs. Hence, its jaw would only need to be strong enough to tear flesh from a carcass, and even then the strong arms could also be used to break a carcass into smaller, manageable pieces. Some palaeontologists did suggest that Dilophosaurus was a scavenger, but as no living large animal exists entirely by scavenging this hypothesis has been rejected. A later theory suggested that the jaws weren't used for killing prey, but rather holding prey. Dilophosaurus lived alongside many smaller animals ranging from herbivorous dinosaurs to frogs, so they would be its primary food source. A Dilophosaurus would catch a small animal where its front teeth would slash the prey, by the time it reached the back of the jaws the prey would be too weak to resist. Andrew Milner and James Kirkland in 2000 suggested a new theory which has become increasingly accepted. The Kayenta Formation has been discovered to be rather wet, and many fish fossils have been found there. Most importantly, wading marks have been found from carnivorous dinosaurs indicating the diet of Dilophosaurus: fish. The strong arms show signs of being even able to grip prey so a diet of fish would be ideal. Like a bear, Dilophosaurus would wade into water where it would swipe up fish to eat in its weak jaws. Milner and Kirkland have found that Dilophosaurus had similar adaptations to the known fish-eating Spinosaurus: long teeth near the front of the skull to hold fish in place; long and strong arms; and nostrils further back in the skull to avoid water entering them. It is therefore likely that Dilophosaurus waded into water to catch fish and other aquatic life.

When and Where

The reconstructed model 'Dyzio' in the Geological Museum of the State Geological Institute in Warsaw

Dilophosaurus lived 193 million years ago in the Early Jurassic. Dinosaurs had begun to fully evolve as a distinct group during the Mid to Late Triassic, and the Late Triassic extinction left them as the dominant terrestrial group. At this time most of the best known dinosaur orders - like stegosaurids, sauropods, and tyrannosaurids - had yet to evolve. Dilophosaurus would have been one of the largest carnivores, especially as large terrestrial life had yet to bounce back from the Triassic-Jurassic extinction. This is also a reason why Dilophosaurus likely had a diet consisting of fish: there were few large herbivorous dinosaurs to hunt. We have currently only found Dilophosaurus in Arizona, but the formation group which the Kayenta Formation is part of comprise most of the South-west United States. We probably could have seen Dilophosaurus in this region as well. Unlike contemporary Arizona, the Kayenta Formation was humid and wet with plenty of lakes and rivers. Rivers preserve fossils well as the sediment protects specimens from the elements. The high number of well preserved specimens, including the first Dilophosaurus to be found, and high number of aquatic animals in the area show this. Dilophosaurus lived in an environment closer to modern Florida than modern Arizona.

Thank you for reading. The sources I have used are as follows:

-Gregory S. Paul, The Princeton Field Guide to Dinosaurs, Second Edition, (Princeton: Princeton University Press, 2016)

-S.P. Welles, 'New Jurassic Dinosaur from the Kayenta Formation of Arizona', GSA Bulletin, 65:6, (1954), 591-598

-S.P. Welles, 'Dilophosaurus (Reptilia: Saurischia), A New Name for a Dinosaur', Journal of Paleontology, 44:5, (1970), 989

-S.P. Welles, 'Dilophosaurus wetherilli dinosauria theropoda osteology and comparisons', Palaeontographica Abteilung A Palaeozoologie-Stratigraphie,185:4-6, (1984), 85-180

-Robert Gay, 'New specimens of Dilophosaurus wetherilli (Dinosauria: Theropoda) from the early Jurassic Kayenta Formation of northern Arizona', Western Association of Vertebrate Paleontologists Annual Meeting Volume Mesa, Arizona, 1:1, (2001)

-'Dilophosaurus', Prehistoric-Wildlife.com, [Accessed 12/07/2019]

-Phil Senter and Sara Juengst, 'Record-Breaking Pain: The Largest Number and Variety of Forelimb Bone Maladies in a Theropod Dinosaur', PLoS ONE, 11:2, (2016), 1-13

-Martin Kundrat, 'When did Theropods Become Feathered? - Evidence for Pre-Archaeopteryx Feathery Appendages', Journal of Experimental Zoology Part B: Molecular and Developmental Evolution, 320B:4, (2004), 355-364

-Andrew Milner and James Kirkland, 'The Case for Fishing Dinosaurs at St. George Dinosaur Discovery Site at Johnstone Farm', Survey Notes of the Utah Geological Survey, (2007), 39, 1-3

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