Dilophosaurus

About Dilophosaurus

Characteristics and the Latest Form

Dilophosaurus was a carnivorous dinosaur that lived in what is now the North American continent during the Early Jurassic period, about 193 to 183 million years ago. Reaching a total length of about 6-7 meters and a weight of about 300-400 kilograms, it was one of the largest land animals in North America at the time and a predator that reigned at the top of the ecosystem.

For many years, there was a misconception that it had "weak jaws and scavenged for carrion," but a comprehensive reassessment study published in 2020 revealed that it was a highly active hunter with a robust skull supporting powerful jaw muscles and a sophisticated bird-like respiratory system.

Dilophosaurus: The Secret of the Crests on its Head

The pair of crests on the top of its head, the most distinctive feature of Dilophosaurus, were initially thought to be "crushed skulls during the fossilization process" or "thin, fragile bone plates" when first discovered.

However, CT scan investigations of the internal structure revealed that the crests were hollow like a honeycomb, making them a lightweight yet sturdy structure.

Role of the crests
It is thought that in life, they were covered with keratin like a hornbill, making them look even more flamboyant. It has been pointed out that they may have been used for visual appeal (display) among peers, thermoregulation to release heat generated by their large bodies, or even as a resonator connected to the nasal cavity and air sacs to produce low rumbling calls.

Skull and Powerful Jaws

Looking at the skull of Dilophosaurus from the side, you can see a strange notch (subnarial gap) between the premaxilla and the maxilla. In the past, it was thought that this notch made its jaw force weak, preventing it from killing large living prey.

However, recent research has found that these bones were intricately interlocked to form strong joints and were not a weak point. The back of the lower jaw was also very heavy and had powerful muscles attached to it.
Fossils of Sarahsaurus, an early sauropodomorph about 4 meters long that lived during the same period, show large bite marks left by Dilophosaurus, indicating that it actively hunted large prey.

Bird-like Respiratory System and High Physical Ability

Many cavities have been found in the neck and back bones of Dilophosaurus. These are traces of an advanced respiratory organ called "air sacs," which modern birds have, penetrating deep into the bones.

This system allowed Dilophosaurus to continuously take abundant oxygen into its body, enabling strenuous exercise. It is also known that it grew at an astonishing rate of 30-35 kilograms per year, leading to the belief that it was an endothermic (warm-blooded) animal with high metabolic capabilities, rather than an ectothermic animal like modern reptiles.

Classification of Dilophosaurus

The phylogenetic placement of Dilophosaurus has been a subject of debate for many years, bouncing between coelophysoids and ceratosaurs.

However, a phylogenetic analysis in 2020 confirmed that it belongs to a group called "non-averostran neotheropods," positioned just before the evolution that led to later giant carnivorous dinosaurs (tetanurans) like Allosaurus and Tyrannosaurus. "Dilophosaurus sinensis," once discovered in China, has now been reclassified into a different genus, and Dilophosaurus is considered a unique dinosaur that lived only on the North American continent.

The Harsh Struggle for Survival Told by Fossils

The first specimen (holotype) discovered in 1942 has become one of the world's leading materials conveying the harsh ecology of theropods to the present day. At least eight severe pathological lesions were found in the left arm and shoulder of this individual, including fractures and a massive pus hole caused by an infection. It is believed that as a result of overusing its right side to compensate for the pain of the injuries, a deformity and a bone tumor developed in its right arm as well.

Surprisingly, traces of "healing" remained in all of these fatal injuries. The fact that this individual survived for weeks to years in agonizing pain, unable to use either arm properly, proves the astonishing vitality and immunity possessed by theropods of that time.

Discovery and Paper Description

In 1942, when the University of California Museum of Paleontology conducted fossil excavations on the Navajo Indian Reservation in Arizona, a well-preserved skeletal specimen was discovered. In 1954, paleontologist Samuel Welles of the expedition team described this as a new species of the known genus Megalosaurus, "Megalosaurus wetherilli."
Later, in 1964, Welles discovered a more complete adult fossil in the same area, and during the cleaning process, it was revealed that it had a pair of crests on the top of its head. Welles described this surprise as being "like finding wings on a worm."

Based on this distinct feature, which differed from Megalosaurus, it was re-described in 1970 as a new genus, "Dilophosaurus," meaning "two-crested lizard."

Fiction in Movies and the True Form

By appearing in the 1993 movie "Jurassic Park," Dilophosaurus instantly became one of the most famous dinosaurs in the world.

However, the features depicted in the movie, such as "spitting venom" and "expanding a neck frill for intimidation," are all fictions created to enhance the film's presentation. No fossil evidence of venom glands or bones supporting a frill has been found. Also, while depicted in the movie as a dinosaur slightly smaller than a human, it was actually a giant hunter reaching about 6-7 meters in length.

Dilophosaurus Stamp and Fossil Gallery