Tyrannosaurus

A Mysterious Ecology: Hunter or Scavenger?

For many years, there has been a fierce debate over whether Tyrannosaurus was a hunter that actively chased its prey or a scavenger that feasted on carrion.
A prominent theory suggests that its massive body would have made it difficult to run fast, though based on its skeleton and muscle mass, it is estimated to have been able to reach speeds of up to 20 km/h, which is still slower than a car.
In contrast, others argue that such a speed would not have been enough to catch prey like Triceratops or Edmontosaurus, and they theorize it could have reached up to 40 km/h over short distances.

A Tyrannosaurus Intimidating Its Prey

However, many scientists believe that Tyrannosaurus was an “opportunist,” performing both roles, much like modern carnivores.
It would have been difficult for it to sustain its enormous body on scavenging alone. To support its size, it needed a considerable amount of meat and is believed to have consumed up to 230 kg of meat at a time.

Unmatched Bite Force and a Destructive Diet

Any prey caught in Tyrannosaurus’s powerful jaws and sharp, large teeth would have had little chance of escape.
Analysis of excavated fossils has shown that its bite force could reach up to 5 tons, which is a mind-boggling amount compared to the average human male’s bite force (261 Newtons).
Tyrannosaurus’s biting force is predicted to have been between 35,000 and 57,000 Newtons.

It Had a Powerful Jaw and Sharp Teeth.

This overwhelming force allowed it to crush its prey’s bones.
This power is evidenced by its fossilized dung, which contains finely crushed bones, as well as bite marks left on the bones of its prey, such as Triceratops and Edmontosaurus.

Triceratops and Edmontosaurus Were Its Prey.

Prey that was bitten would either die from shock due to severe wounds or from massive blood loss.

Physical Structure and Latest Findings: Overturning Conventional Wisdom About Its Appearance

A defining feature of Tyrannosaurus was its massive head, which was about 1.5 meters long—more than 10% of its body length—and its sharp teeth, with the longest reaching 30 cm.
Some teeth, with a visible length of up to 14 cm from the gum, had serrations like a steak knife, which allowed them to easily tear through meat.
While most carnivorous dinosaurs had thin teeth, Tyrannosaurus’s teeth were so robust they could pierce bone, and if a tooth broke, a new one would grow in its place.

In contrast to its enormous head, its forelimbs were extremely short, with only two fingers.

Its Arms Were Short, and It Had Only Two Fingers.

The forelimbs were so short they couldn’t even touch each other, but it is believed that they had a certain amount of strength and may have helped it stand up from a resting position or held prey in place.
At the “Super Carnivore T.Rex” exhibition in 2016, it was suggested that it may have been able to lift about 200 kg with one hand.

Its hind limbs, characterized by strong thighs and slender shins and ankles, were a structure unique to fast-moving creatures. It is thought that younger individuals were particularly fast.
While it was once depicted dragging its tail like Godzilla, it actually walked in a nearly horizontal posture, with its head thrust forward and its long tail held straight back for balance.

It Walked in a Nearly Horizontal Posture.

Its vision was also exceptional; because its eyes faced forward, it had binocular vision, much like humans. This was well-suited for accurately judging the distance and speed of its prey. Research on its skull also shows that its brain had a highly developed visual system. Its eye sockets were narrow and vertically divided in a keyhole shape to prevent its eyes from being injured by prey.

Feathers and Facial Appearance: The Forefront of Scientific Debate

The debate over whether Tyrannosaurus had feathers is still unresolved.
Since traces of feathers have been found on related small theropods and a large 8-meter theropod (Yutyrannus), one theory suggests that juveniles, which had difficulty regulating their body temperature, may have had feathers.

A Feathered Tyrannosaurus.

According to this theory, they were covered in feathers when they were small to stay warm, but lost them as they grew to release heat.
However, a paper published in 2017 proposed that they were covered in scales.

Furthermore, the well-preserved “Dueling Dinosaurs” fossil provides direct evidence that the soles of the feet and other parts were covered in reptile-like scales.

In recent years, a new theory has gained significant attention, suggesting that Tyrannosaurus had lips covering its teeth, overturning the image of its ferocious face.
A study published in 2023 pointed out that the enamel on its teeth was thin, and if its teeth were exposed like a crocodile’s, they would have dried out and become damaged.
Instead, the study concludes that it is highly likely that its teeth were covered by thin, scaly lips, similar to a modern monitor lizard, to keep them moist.

Growth, Lifespan, and Social Behavior: Surprising Aspects

A dinosaur’s age can be estimated by examining the growth rings in a cross-section of its fossilized bone.
The lifespan of a Tyrannosaurus is estimated to be around 30 years.
When they hatched from the egg, they were only about 60 cm long and weighed just 2 kg.
However, it’s believed that 60% of individuals died by the age of two, indicating a very high juvenile mortality rate.
Survivors are thought to have gained about 2.1 kg per day during a growth spurt between the ages of 14 and 18, putting on 3,000 kg in just four years.
Fossil evidence also shows that as they approached 30, many individuals suffered from injuries and joint diseases.

Whether Tyrannosaurus was a solitary hunter or hunted in packs has also been a subject of long debate.
Bone beds where multiple tyrannosaur fossils were found together have been discovered in Canada and the United States, providing strong evidence that they may have lived in groups.
Tyrannosaurus may have built a sophisticated social structure, much like wolves, where experienced adults led and taught the younger ones how to hunt.
Evidence of cannibalism has also been inferred from bite marks left on fossils.
In particular, traces have been found that suggest the bites occurred while the dinosaur was still alive, indicating that cannibalism was a regular occurrence.

According to a 2021 paper, the population density of Tyrannosaurus was estimated to be one per 6-kilometer radius, suggesting that about 20,000 individuals existed at any given time across all of North America.
Calculations also suggest that a total of 2.5 billion individuals existed over a period of about 2 to 3 million years, speaking to its immense success.

Discovery of New Species and Taxonomic Shifts

For a long time, the genus Tyrannosaurus was thought to contain only a single species, rex, which is why the name “Tyrannosaurus rex” or its shorthand “T-Rex” is so widespread.
However, in 2022, a theory was proposed that the genus should be split into three species—Tyrannosaurus rex, Tyrannosaurus regina, and Tyrannosaurus imperator—based on differences in skeletal robustness and tooth shape.
While this theory has been met with much debate, it sparked an interesting discussion about the individual variations that existed within Tyrannosaurus.

Then, in 2024, a new species was formally described based on a fossil discovered in New Mexico, USA: Tyrannosaurus mcraeensis. This was a major headline.
This new species is believed to have appeared about 6 to 7 million years earlier than Tyrannosaurus rex, making it a crucial discovery for unraveling the mystery of Tyrannosaurus’s evolution.

Valuable Fossil Specimens: “Sue” and “Dueling Dinosaurs”

Dozens of Tyrannosaurus fossils have been found to date, but none are considered a complete specimen.
However, the Field Museum in Chicago, USA, displays “Sue,” known as the most expensive dinosaur skeleton in history.
Purchased at auction for about 900 million yen in 1997, Sue is a valuable specimen that helps us understand the appearance of Tyrannosaurus today.

Also, the “Dueling Dinosaurs” specimen, a fossilized Tyrannosaurus intertwined with a Triceratops, boasts an astounding preservation rate of nearly 100% skeletal completeness.
Research on this fossil is still ongoing, as it has the potential to settle the long-running debate over whether the small tyrannosaurid “Nanotyrannus” was a separate species or simply a juvenile Tyrannosaurus.