Dilophososaurus lived around 193 million years ago, during the Early Jurassic. It can be said, that it was one of the earliest large predatory dinosaurs. This genus of theropods were named after the two crests on its skull, and the genus name means "two-crested lizard". Its type species is Dilophosaurus wetherilli, described by Samuel P. Welles in 1954. The species name wetherilli came from John Wetherill, a Navajo councilor, a friend of the exploring scientists. Its habitat was situated in North America, and it was the greatest known apex predator in its age.

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Dilophosaurus wetherilli. By Leandra Walters, published by Phil Senter and James H. Robins - http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0144036, CC BY 2.5, https://commons.wikimedia.org/w/index.php?curid=47545507

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Known occurrences of Dilophosaurus wetherilli fossils.

Discovery and fossil history

The University of California Museum of Paleontology organized an expedition for fossil vertebrates in northern Arizona, in 1942, because they were informed by Wetherill's nephew that promising bones were resting in the ground. Navajo Jesse Williams led them to the location of interesting remains he found two years earlier. The Navajo held a myth about the remains, according to which the corpses of the slain monsters were once buried in the ground and could not or should not be taken out. This are belonged to the Kayenta Formation.

There were three dinosaur skeletons, one of them was surprisingly intact although the skull was destroyed. It took for three researchers for two years to clean and mount it up. A member of the exploration group, the paleontologist Samuel P. Welles orginally described this dinosaur as Megalosaurus wetherilli, in 1954. At the time, the taxon of Megalosaurus was used as a wildcard, dinosaurs believed to be unclassifiable were placed there.[1][2][3][4][5][6]

Ten years later, Welles returned to the area. He determined the age of the concerned geological layer and explored an additional skeleton. In this instance, it was clarified it would have had two crests on the top of its skull. It was a completely unexpected surprise for the researchers. In case of the earlier remains, these crests were believed to be the destroyed part of the cheekbone as such a phenomenon was previously unknown to dinosaurs and it stirred the world of paleontologists. In 1970, Welles created the genus Dilophosaurus. [7][8][9][10][11]

The Dilophosaurus was the first well-known theropod and its fossils specimens belonged to the best-preserved ones from this period.[4] An infant specimen was also identified from a 1978 collection in the early 2000s, which became one of the earliest known infant theropods from the continent. [10]

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Dilophosaurus wetherilli skeleton. By Emily Willoughby - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=31371130

Taxonomy and valid species

The only valid species of the genus is Dilophosaurus wetherilli. Another species, Dilophosaurus sinensis was also described in 1993, but it was later transferred to the genus Sinosaurus. Welles originally classified Dilophosaurus as a megalosaur, however in 1970, after recognizing the crests, he reconsidered his theory.[2][7] He and the paleontologist Robert A. Long determined Dilophosaurus to be a ceratosauroid. Welles found it to be closest to Halticosauridae, in particular Liliensternus. In 1988, halticosaurs began to be treated as a subfamily of Coelophysidae. It had been suggested that Dilophosaurus is a direct descendant of Coelophysis. Furthermore, the scientific world was preoccupied with the possibility that spinosaurs were late-surviving dilophosaurs. They were later classified in the group Coelophysoidea as the only member of the family Dilophosauridae, and Coelophysoidea was placed in the group Ceratosauria.[1][13][14]

Since then, there have been many debates and versions regarding its exact taxonomic classification, but according to the current scientific position Dilophosaurus is a member of the family Dilophosauridae along with Dracovenator, a group placed between the Coelophysidae and later theropods. [5]

Description and anatomy

Dilophosaurus was about 6-7 meters long and it weighed about 280-400 kilograms.[14][15] It is supposed that it could grow quickly, gaining up to 30 kilos a year at the beginning of its life. The entire animal was slender and light in structure, its neck was flexible and relatively long. It had relatively large but delicate and narrow skull. Compared to other theropods the nostrils were placed further back. On its skull roof it bore a pair of longitudinal crests. These can be described as curved, thin and tall and were mainly formed by lacrimal and nasal bones. Welles thought these were similar to the crest of cassowary, while others believed the crests were covered in keratin which made them bigger. Since the crests was only intact on one specimen, the question remains whether they differed from invidual to invidual. In the crests, in the vertebrae and in the bones that surrounded the brain there were air sacs. The teeth were thin, curved back and long covered with a layer of enamel. The jaws contained replacement teeth.[1][4][5][16]

The hands had four fingers: the first was shorter but stronger with a large claw, and the following fingers were longer and more slender, with smaller claw. It had three clawed toes on its long, stout legs. In its fossil traces, some researchers thought they discovered the imprints of feathers.[1][5][17] Contrary to pop culture depictions, it's clear it had not frill and it could not spit venom, however, it is possible that its bite was poisonous, as has been claimed for the Komodo dragon.[18]

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Dilophosaurus wetherilli. By Heather Kyoht Luterman - Milner ARC, Harris JD, Lockley MG, Kirkland JI, Matthews NA (2009) Bird-Like Anatomy, Posture, and Behavior Revealed by an Early Jurassic Theropod Dinosaur Resting Trace. PLoS ONE 4(3): e4591. doi:10.1371/journal.pone.0004591, CC BY 2.5, https://commons.wikimedia.org/w/index.php?curid=6091279

Paleobiology and paleoecology

Welles thought that this dinosaur could have killed with its claws, but it was more of a scavenger because he found the teeth were only suitable for cutting up meat. However, later Robert T. Bakker proved with the newly found findings that the jaws of the Dilophosaurus could tear apart any contemporary herbivore. Presumably they preferred the smaller ones, which they killed similar to the biting habits of crocodiles. This theropod was a fast and agile hunter thanks to its unidirectional breathing among other factors.[1][19][20] Its bone injuries also confirm its very active predatory lifestyle and the fact that it must had been under a lot of stress in its habitat. It is considered likely that it also consumed fish. Although it walked on two legs, its front legs may also have had an important function, for example in grabbing food and lifting it to its mouth. Its physique also proved to be suitable for moving in water. It is conceivable, but not proven, that they lived in groups.[21][22][23]

As for the function of the crests, Welles suggested they could have been used for thermoregulation, species recognition and sexual selection, that is why they could be colorful. The crests were definitely weak for fighting. More findings would be needed to reveal how different were the crests by gender or age.[1][24][25][26]

In connection with its habitat, the environment had been likened to a river oasis; a waterway surrounded by sand dunes and lined with conifers resulted in a small but species-rich community of living beings.[16][27]

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Dilophosaurus wetherilli, mounted model. By Wikipek - Own work by Author - photography taken in the Geological Museum of the Polish Geological Institute in Warsaw, CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=7540067

Author: Csenge Lugosi, Biologist BSc student

Scientific references

[1]: Welles, S.P. (1984): Dilophosaurus wetherilli (Dinosauria, Theropoda), osteology and comparisons. Palaeontographica Abteilung A, 185: 85-180.

[2] Welles, S.P. (1954): New Jurassic dinosaur from the Kayenta Formation of Arizona. Bulletin of the Geological Society of America, 65 (6): 591-598. doi: 10.1130/0016-7606(1954)65[591:NJDFTK]2.0.CO;2.

[3] Welles, S.P.; Guralnick, R.P. (1994): Dilophosaurus discovered. ucmp.berkeley.edu. University of California, Berkeley.

[4] Naish, D. (2009): The Great Dinosaur Discoveries. London, UK: A & C Black Publishers Ltd. pp. 94-95. ISBN 978-1-4081-1906-8.

[5] Marsh, A.D.; Rowe, T.B. (2020): A comprehensive anatomical and phylogenetic evaluation of Dilophosaurus wetherilli (Dinosauria, Theropoda) with descriptions of new specimens from the Kayenta Formation of northern Arizona. Journal of Paleontology, 94 (S78): 1-103. doi: 10.1017/jpa.2020.14.

[6] Mayor, A. (2005:. The Southwest: Fossil fetishes and monster slayers. Fossil Legends of the First Americans. Princeton, NJ: Princeton University Press. pp. 130-143. ISBN 978-0691130491.

[7] Welles, S.P. (1970): Dilophosaurus (Reptilia: Saurischia), a new name for a dinosaur. Journal of Paleontology, 44 (5): 989.

[8] Welles, S.P.; Guralnick, R.P. (1994): Dilophosaurus Details. ucmp.berkeley.edu. University of California, Berkeley. Archived from the original on August 2, 2017.

[9] Glut, D.F. (1997): Dinosaurs: The Encyclopedia. Jefferson: McFarland & Company, Inc. pp. 347-350. ISBN 978-0786472222.

[10] Rauhut, O.W. (2004): The interrelationships and evolution of basal theropod dinosaurs. Special Papers in Palaeontology. 69: 213.

[11] Gay, R. (2001): New specimens of Dilophosaurus wetherilli (Dinosauria: Theropoda) from the early Jurassic Kayenta Formation of northern Arizona. Western Association of Vertebrate Paleontologists Annual Meeting. Vol. 1. Mesa, Arizona. p. 1.

[12] Welles, S.P.; Long, R.A. (1974): The tarsus of theropod dinosaurs [Annals of the South African Museum]. Annale van die Suid-Afrikaanse Museum, 64: 191-218. ISSN 0303-2515

[13] Paul, G.S. (1988): Predatory Dinosaurs of the World. New York, NY: Simon & Schuster. pp. 258, 267-271. ISBN 978-0-671-61946-6.

[14] Holtz, T.R., Jr. (1994): The phylogenetic position of the Tyrannosauridae: Implications for theropod systematics. Journal of Paleontology, 68 (5): 1100-1117. doi: 10.1017/S0022336000026706.

[15] Paul, G.S. (2010): The Princeton Field Guide to Dinosaurs. Princeton, NJ: Princeton University Press. p. 75. ISBN 978-0-691-13720-9.

[16] Brown, M. A.; Marsh, A. D. (2021): The real Dilophosaurus would have eaten the Jurassic Park version for breakfast. Scientific American. 324 (1): 46-53. doi: 10.1038/scientificamerican0121-46.

[17] Gierliñski, G. (1996): Feather-like impressions in a theropod resting trace from the Lower Jurassic of Massachusetts. Museum of Northern Arizona Bulletin, 60: 179-184.

[18] Bennington, J.B. (1996): Errors in the movie Jurassic Park. American Paleontologist. 4 (2): 4-7.

[19] Bakker, R.T. (1986): The Dinosaur Heresies. New York, NY: William Morrow. pp. 263-264. ISBN 978-0-8217-5608-9.

[20] Therrien, F.; Henderson, D.; Ruff, C. (2005): Bite me - biomechanical models of theropod mandibles and implications for feeding behavior. In Carpenter, K. (ed.). The Carnivorous Dinosaurs. Indiana University Press. pp. 179-230. ISBN 978-0-253-34539-4.

[21] Rothschild, B.; Tanke, D.H.; Ford, T.L. (2001): Theropod stress fractures and tendon avulsions as a clue to activity. In Tanke, D.H.; Carpenter, K. (eds.). Mesozoic Vertebrate Life. Bloomington, IN: Indiana University Press. pp. 331-336. ISBN 978-0253339072

[22] Milner, A.; Kirkland, J. (2007): The case for fishing dinosaurs at the St. George Dinosaur Discovery Site at Johnson Farm. Survey Notes of the Utah Geological Survey. 39: 1-3.

[23] Senter, P.; Sullivan, C. (2019): Forelimbs of the theropod dinosaur Dilophosaurus wetherilli: Range of motion, influence of paleopathology and soft tissues, and description of a distal carpal bone. Palaeontologia Electronica. doi: 10.26879/900.

[24] Padian, K.; Horner, J.R. (2011): The evolution of 'bizarre structures' in dinosaurs: Biomechanics, sexual selection, social selection or species recognition? Journal of Zoology. 283 (1): 3-17. doi: 10.1111/j.1469-7998.2010.00719.x.

[25] Coombs, W.P. (1990): Behavior patterns of dinosaurs. In Weishampel, D.B.; Osmolska, H.; Dodson, P. (eds.). The Dinosauria (1st ed.). Berkeley, CA: University of California Press. p. 42. ISBN 978-0-520-06727-1.

[26] Czerkas, S.J.; Czerkas, S.A. (1990): Dinosaurs: A global view. Limpsfield: Dragons' World. p. 208. ISBN 978-0-7924-5606-3.

[27] Lucas, S.G.; Heckert, A. B.; Tanner, L.H. (2005): Arizona's Jurassic fossil vertebrates and the age of the Glen Canyon Group. New Mexico Museum of Natural History Bulletins. 29: 95-104.