Unique Horns and Defense Mechanism

The most distinctive feature of Albertaceratops was the unique arrangement of its horns.
While many other ceratopsians had a large horn on their nose, Albertaceratops had two large horns on its brow and two large horns on the top of its frill.

It had two large horns on its brow and two more on the top of its frill.

These horns are believed to have helped protect it from the biting attacks of Tyrannosaurus.
It may also have swung its head from side to side, using its horns like a pickaxe.

It may have swung its head from side to side, using its horns like a pickaxe.

This unique defense mechanism suggests that Albertaceratops had its own unique survival strategy within its ecosystem.

Confusion Surrounding Its Naming

Before being officially described, Albertaceratops was for a time referred to by the name Medusaceratops.
However, the name Medusaceratops is now used for a different ceratopsian genus.

Thus, based on its unique horn arrangement, it is speculated that Albertaceratops had its own distinct defensive strategy in its ecosystem.
Future discoveries of more fossils are expected to unravel the remaining mysteries of this dinosaur.

Impenetrable Defense and the Ultimate Weapon

The greatest strength of Ankylosaurus was its thorough defense.
Its back was covered in a hard, bony shield (osteoderms), like a suit of armor, from which countless horns protruded.
The bones of its skull were also thick, and it even had bony armor over its eyelids, leaving almost no weak points.
This impenetrable defense was like an “unassailable moving fortress.”

An unassailable moving fortress

It is believed that even a large carnivorous dinosaur like Tyrannosaurus would have hesitated to attack a fully grown Ankylosaurus.

Furthermore, at the end of its tail, Ankylosaurus had a giant mass of bone, a hammer known as a “tail club.”
The bones in the latter half of the tail were fused together, forming a stiff handle for swinging the hammer.
This allowed it to swing the club from side to side at a powerful speed, using the flexible muscles at the base of its tail.

It could swing the hammer from side to side at a powerful speed

According to a 2009 study, a single blow from this hammer could generate a force of up to 364 to 718 MPa (megapascals), which was powerful enough to shatter the leg bones of a Tyrannosaurus.
The height of the tail was right at a Tyrannosaurus‘s knee, so a direct hit could inflict serious damage.
Ankylosaurus compensated for its weakness of being a slow walker with this hard armor and powerful weapon, allowing it to thrive for millions of years.

A Mysterious Full Body and a Unique Diet

Despite being so famous, no complete skeleton of Ankylosaurus has ever been discovered, making it a dinosaur shrouded in mystery.
Our knowledge of its appearance is a reconstruction based on fragmentary fossils like skulls and armor, as well as research data from its close relative Euoplocephalus, for which a more complete fossil record exists.

Ankylosaurus was a herbivore with a beak-like snout.
Its teeth were small and weak, so it could not chew hard plants. It appears to have eaten plants, such as ferns, by plucking them with its wide beak and swallowing them almost whole.
According to a 2017 study, it is estimated to have needed about 60 kg of ferns per day.

It is estimated to have needed about 60kg of ferns per day

The Secret of Its Surprising Skull and a History of Success

A CT scan of an Ankylosaurus skull revealed a complex interior of its nasal passages.
The air passage deep inside its nose was divided into eight small chambers, leading to the interesting theory that it functioned as an “air conditioner” to warm and humidify inhaled air, or as a “resonating chamber” to produce loud calls.

Ankylosaurus is one of the most famous dinosaurs of the late Cretaceous period, but one reason a complete skeleton has not been found in over a century is the theory that its population was originally very small.
If this theory is correct, it means that they lived with a limited population even in their heyday.
As evidence, no Ankylosaurus fossils have been excavated from the very end of the Cretaceous period, leading some to believe that it was one of the few dinosaur species that “did not witness the moment of mass extinction.”

A Unique Appearance with a Shield and Spikes

Antarctopelta was a heavily armored dinosaur, its body covered with shield-like bony plates and many thick spikes.
Its appearance was similar to that of early ankylosaurids, but it lived much later.
This is believed to be the result of it being isolated from other ankylosaurids early on, allowing it to undergo a unique evolution in the special environment of Antarctica.

A Dinosaur Still Shrouded in Mystery

Currently, only very fragmentary fossils of Antarctopelta have been discovered, including vertebrae, a lower jaw, and a few teeth.
As a result, much about its complete appearance and ecology remains a mystery.
In particular, it is not yet known whether it had a hammer-like bone club at the end of its tail, like Ankylosaurus.

Antarctopelta is a very interesting dinosaur due to its unique evolution in the special environment of Antarctica.
It is hoped that future research will reveal the full picture of this mysterious armored dinosaur.

Origin of the Name and Basic Data

The scientific name Aquilops is derived from a combination of Latin and Ancient Greek.

Meaning of the Name

Latin for “Eagle” (aquila) + Ancient Greek for “Face” (ops) = “Eagle Face”

Type Species

Aquilops americanus

This specific name was chosen to commemorate the fact that it was the first “very basal neoceratopsian” discovered in the United States.

History from Discovery to Naming: Recognized as a New Species After 17 Years

The first fossil of Aquilops was discovered in 1997.
An expedition supported by National Geographic excavated a single partial skull from the Cloverly Formation (Albian stage) in Carbon County, southern Montana.
The discoverer was paleontologist Scott Madsen.

Was it Mistaken for Another Dinosaur at First?

It was not introduced to the world as “Aquilops” immediately upon discovery.
Initially, while the specimen was undergoing preparation, it was described as a different dinosaur, Zephyrosaurus.
Later, Madsen himself realized it was a new species, but it took a long time for it to be formally recognized.

Finally, in 2014—17 years after its discovery—it was named and described by Andrew Farke and colleagues, etching the name Aquilops into history.

Only 60cm Long! Physical Characteristics of the “Eagle Face”

Aquilops was a very small dinosaur.
According to estimates by paleontologist Mathew Wedel, its dimensions were as follows:

• Total Length: Approx. 60 cm
• Weight: Approx. 1.5 kg
• Skull Length: 84.2 mm (Holotype specimen OMNH 34557)

Unique Features Proposed by the Describers

As its name implies, Aquilops possessed unique facial features.

An Eagle-like Beak

This is the most defining feature of Aquilops.
The bone core of the beak curves downward, and the front possesses an arched keel with a bump.

Distinctive Dentition

The tooth row in the back of the upper jaw, when viewed from the front, is longer than the entire length of the depression seen from the side.

Pointed Antorbital Fenestra

The antorbital fenestra (the opening in front of the eye socket) is twice as long as it is tall, pointing backward and extending beneath the eye socket.

Classification and Evolution: Between Psittacosaurus and Protoceratops

Taxonomically, it is considered to have occupied a position more advanced than the famous ceratopsian Psittacosaurus, but more primitive than Protoceratops.
As a very basal neoceratopsian, it is a crucial piece of the puzzle in understanding the evolutionary process of horned dinosaurs.

Remaining Mysteries: No Frill or Body Found?

Many mysteries still surround the detailed ecology of Aquilops.

Only “Part of the Head” Has Been Found

To date, only a partial skull including the upper and lower jaws has been discovered.
Most of the back of the head and the palate are missing. Not only are the body bones—necessary to know the dinosaur’s full appearance—missing, but even the “frill,” a symbol of ceratopsians, has not been found.

The Specimen Was Likely a “Child”

Furthermore, the discovered holotype specimen itself is likely not a fully mature individual, but a “sub-adult.”
Studies comparing it with related species suggest this specimen was about 60% of the size of an adult.

In other words, the Aquilops we know is still in the growth phase, and no one yet knows what a fully grown adult looked like.

Hopes for Further Discoveries

Due to the extremely low number of specimens—and the fact that only partial sub-adult fossils have been found—the full picture of Aquilops remains unclear.
To understand the true appearance of this mysterious dinosaur with the “Eagle Face,” further fossil discoveries are essential.

A Swift Herbivore

Atlascopcosaurus was a quick-footed herbivore with a highly agile nature.
It spent most of its life eating plants and running away from carnivorous dinosaurs.
It is also suggested that they lived in family groups or small herds, protecting each other while they lived.

A Difficult Excavation and a Mysterious Appearance

The fossil of Atlascopcosaurus was discovered in a place called “Dinosaur Cove” in Victoria, southern Australia.
The area is made up of hard rock near the coast, and the fossil excavation was an extremely difficult task that involved digging tunnels underground.

The only fossils found so far are a nearly complete upper jaw and about 50 other bone fragments, so many details remain unknown, making it a dinosaur shrouded in mystery.
However, it is thought to have been a very small and primitive species within the Hypsilophodontidae family.

If more fossils are discovered in the future, the full picture of Atlascopcosaurus may be revealed.
There is great anticipation for future research to uncover how this uniquely named dinosaur lived.

“Pointed Lizard”: The Misunderstandings and Truths Hidden in the Name

The scientific name Centrosaurus means “pointed lizard” in Greek.
Looking at their characteristic “large single horn on the nose,” the name seems fitting, but there is actually a somewhat complex story behind it.

Not a Nose Horn, but “Part of the Frill”?

At the time of naming in 1904, the specimen referenced was not the nasal horn but “part of the frill.”
Researchers mistakenly interpreted a hook-like projection on the rear edge of the frill as a “horn on the nose.”
The misunderstanding was later cleared up, but since they actually possessed a magnificent nasal horn, the name and the reality ended up matching perfectly.

Confusion Over the Name

Also, since the name was already used for a type of lizard at the time of naming, an attempt was made to rename it “Eucentrosaurus” (though Centrosaurus is now established for the dinosaur).
Note that although the spelling is similar to the stegosaur “Kentrosaurus,” it is a completely different dinosaur.

The Standard Model of the Centrosaurinae

Centrosaurus is the representative genus of the “Centrosaurinae” subfamily.
It lacks the “long horns above the eyes” seen in Triceratops (Chasmosaurinae), and instead has a developed “long single horn on the nose.”

A “long single horn on the nose” is developed

Nasal Horn

Individual variation is significant; it can curve forward or backward, or stand upright.

Frill

It is relatively short, with hook-like projections (hooks) on the rear curving towards the face.

These are believed to have functioned as displays to peers or “fashion” for species identification.
Their body shape was thick like a barrel, with a stable structure and a low center of gravity.

Alberta’s Bone Beds: A “Wildebeest-like Life” of 10,000

From “Dinosaur Provincial Park” in Alberta, Canada, fossils are discovered in such vast quantities that even if paleontologists from all over the world gathered, they couldn’t dig them all up.

Massive Herds Lost to Muddy Streams

“Bone beds,” where bones are concentrated in specific locations, contain the remains of thousands to ten thousand individuals.
The cause of death is considered to be mass drowning due to “river flooding,” rather than carnivorous dinosaurs or disease.

They migrated seasonally in massive herds, much like modern African wildebeests.
While crossing rivers, they were caught in floods, and the entire herd was swallowed by the muddy stream.
This tragic record is irrefutable evidence that they were highly social animals.

Evolutionary Mysteries and Records of Disease

Horn Evolution and the “Peaceful Resolution” Theory

There is an interesting hypothesis regarding the evolution of the Centrosaurinae.
The theory suggests they evolved from the sharp-horned Centrosaurus to “Achelousaurus” with stump-like horns, and then to “Pachyrhinosaurus” with a massive boss (bump).

Sharp horns carry the risk of inflicting fatal injuries in fights between the same species.
Therefore, it is thought that by evolving into a “boss” used for head-butting matches, they avoided unnecessary killing and ensured the prosperity of the species.

Dinosaurs Also Suffered from Disease

Thanks to the vast number of fossil samples, traces of healed fractures and osteosarcoma (bone cancer) have been found.
Mummified fossils with remaining skin also exist, and their appearance while alive is being revealed in detail.

“Lizard with Large Openings”: Was 80% of the Frill Hollow?

Origin of the Scientific Name

The scientific name “Chasmosaurus” derives from the Greek word “chasma” (meaning large hole or opening), translating to “Opening Lizard” (or “Chasm Lizard”).
Why was it given such a name? One look at its frill—its identity—makes the reason obvious.

Huge “Holes” Occupying Most of the Surface Area

The frill of Chasmosaurus was a massive rectangle reaching over 1 meter in width and 1.5 meters in length, but it was not a “solid shield” like that of Triceratops.
There were gaping openings on the left and right sides; surprisingly, more than 80% of the surface area was hollow (consisting only of a bone frame).

80% of the frill was hollow

The Role of the Massive Frill: Weight Reduction and Display

For what purpose did this massive, hole-filled frill exist?

“Weight Reduction” is Certain

First, “weight reduction” is considered a certainty.
If the entire frill were solid thick bone, it would be too heavy to support with the neck.
By reducing the bone to the absolute limit and opening holes, it is believed they could move nimbly while maintaining a huge ornament.
*In living individuals, these holes were covered by skin and muscle.

The “Display Theory” is the Leading Candidate

Currently, the most dominant theory is that the frill was used as a “billboard (display).”
Blood vessels ran through the skin, and it is possible they flushed blood to change color to intimidate rivals or displayed vivid colors to court the opposite sex.

Defense Theory and the “Defensive Circle”

It was once thought to be a defensive shield, but a frill full of holes is too fragile for physical attacks.
However, in group battles, it may have been a different story.
When attacked by carnivorous dinosaurs, they likely formed a defensive circle like musk oxen, sheltering the children in the center.
It is believed that by facing outward and lining up their massive frills, the adults created a visual “barricade” to intimidate enemies.

The Mystery of the Horns and Herds of 1,000

Horns That Disappear with Growth?

Chasmosaurus possessed three horns on its forehead and nose, but they were not as developed as those of Triceratops.
In recent years, theories such as “supraorbital horns (brow horns) being absorbed and shortened as they grew” or that the differences represent sexual dimorphism (differences between males and females) are being debated.

Bone Beds on a Scale of 1,000

In Alberta, Canada, “bone beds” containing fossils of many individuals gathered in one place have been discovered.
These are traces of entire herds being washed away by floods, suggesting that Chasmosaurus formed massive groups, sometimes reaching up to 1,000 individuals, and lived with a high degree of sociality.

Fossil “Children” That Thrilled Researchers

Chasmosaurus is one of the most thoroughly researched ceratopsians.
The reason lies in the “quality” and “quantity” of the fossils.

Skin and the Discovery of Juveniles

Many high-quality fossils exist, including “skin fossils” with scale impressions.
Furthermore, what delighted researchers was the excavation of multiple well-preserved “child fossils (juveniles).”
It is rare for the fragile bones of juveniles to remain, and this provided valuable clues for understanding changes in body shape (such as head-to-body balance) associated with growth.

Taxonomic Changes and Museums in Japan

Consolidation from 10 Species to 2

In the past, due to individual differences and growth stages, fossils were often classified as separate species, and it was said that over 10 species existed.
Currently, classification has been organized, and the following two are considered the main valid species.

Chasmosaurus belli

Has short supraorbital horns.

Chasmosaurus russelli

A primitive species with supraorbital horns.

Exhibitions in Japan

You can see reconstructed skeletons in Japanese museums, but names may change due to shifts in classification.
For example, a skeleton once labeled as “a species of Chasmosaurus” at the Fukui Prefectural Dinosaur Museum is now considered highly likely to be “Albertaceratops” or “Medusaceratops.” Information is constantly updated alongside research.

A Helmet-Shaped Crest: Its Amazing Functions

The greatest defining feature of Corythosaurus is the magnificent fan-shaped (arched) crest towering atop its head.

The distinctive crest

Despite its unique appearance, this crest had highly advanced functions.

The crest was hard and hollow, with internal tubular passages connecting all the way down to the nostrils.
Its structure is very similar to a brass instrument like a French horn.

It is believed that this crest primarily served the following four roles:

Resonator

As is true for many crested dinosaurs, it has been scientifically proven that Corythosaurus could produce loud sounds.
The tubes inside the swollen crest resonated their calls, and a 1994 study indicated the possibility that it emitted a low sound similar to a trombone (or a steam whistle).
It is thought that this sound was used for communication with the herd or to intimidate other males.

Amplifying the Sense of Smell

The inside of the crest was directly connected to the nasal cavity, and it is believed to have been used as a tool to amplify its sense of smell.

Air Conditioning

As air passed through the inside of the crest, it likely provided adequate moisture to the air drawn into the lungs.

Display

The unique helmet-like shape is thought to have been used to attract the opposite sex or visually distinguish members of its own species.
The particularly high, prominent crests are believed to have belonged to adult males, which strongly supports this theory.

History of Discovery and Progress in Research

The first Corythosaurus fossil was discovered in 1911 (and described in 1914).
It was found along the Red Deer River in Alberta, Canada, by Barnum Brown, who is also famous as the discoverer of Tyrannosaurus.

The First Specimen

The well-preserved fossil discovered at this time (missing only part of the tail and forelimbs) was named “Corythosaurus casuarius.”
The specific name is derived from the scientific name of the cassowary, a bird that sports a similar crest.

Abundant Specimens

Since then, numerous skeletal specimens, including over 20 skull fossils, have been found in the United States and Canada.
These specimens include a variety of individuals—males, females, and juveniles—making it one of the most extensively studied dinosaurs today.

Differences in Sex and Growth

From these specimens, researchers learned that the shape of the crest varied greatly depending on sex and growth stage.
The swelling was not developed in their juvenile stage, and it appears to have grown larger as they matured.

Precious Skin Fossils

Furthermore, even complete skeletons with fossilized skin have been discovered. These serve as an incredibly valuable source of information for understanding exactly what Corythosaurus looked like when it was alive.

Physique and Ecology

Corythosaurus was quite large among hadrosaurs, reaching about 9 to 10 meters (29.5 to 32.8 feet) in length and weighing around 3 metric tons (6,600 lbs).

Diet

They were herbivorous dinosaurs. Their mouths were lined with over 600 teeth (a dental battery), which they used to grind up and eat tough plants.
In fact, fossils have been found with conifer needles, seeds, and twigs remaining in their stomach cavities.

Ancestry

Their ancestor is believed to be the famous Iguanodon.
While Iguanodon itself did not have a crest, its body shape is very similar, supporting the idea that they are descendants.

Tail Characteristics

The caudal vertebrae (tail bones) were stiffened by ossified tendons, and it is thought that the tail had poor mobility.

It is believed that the tail had poor mobility

Relationship with Close Relatives

In Late Cretaceous North America, there were other dinosaurs with similarly crested heads, such as Lambeosaurus and Parasaurolophus.

How to Tell It Apart from Lambeosaurus

Corythosaurus and Lambeosaurus can be distinguished by the shape of their crests.
While the crest of Lambeosaurus points slightly forward like a pompadour hairstyle, that of Corythosaurus swells into an arch shape.

In this way, Corythosaurus is an extremely important dinosaur in an academic sense, and it continues to fascinate many researchers to this day.

“Dragon King of Hogwarts”: A Name Inspired by Harry Potter

“Dragon Bones” That Surprised Even Paleontologists

The fossil of Dracorex was first discovered in 2003 in South Dakota, USA.
Upon seeing the discovered skull, renowned paleontologist Robert Bakker was reportedly astounded by its dragon-like shape and exclaimed, “This is a dragon’s bone!”

Meaning and Origin of the Scientific Name

When formally described in 2006, this dinosaur was given a very unique scientific name:
“Dracorex hogwartsia.”

• Draco: Latin for “Dragon”
• Rex: Latin for “King”
• Hogwartsia: Derived from “Hogwarts School of Witchcraft and Wizardry” in the Harry Potter novel series

In other words, the name means “Dragon King of Hogwarts.”
Thanks to this witty naming and its visuals resembling a fantasy creature, Dracorex instantly captured the hearts of dinosaur fans.

A Shocking Theory: “Does Dracorex Not Exist?”

However, a few years after its discovery, paleontologist Jack Horner, known for supervising the movie Jurassic Park, announced a shocking hypothesis that overturned the existence of this “Dragon King.”

The theory was that “an independent species called Dracorex does not exist; it is merely a juvenile (child) Pachycephalosaurus.”

Basis for the Suspicion

Unlike Pachycephalosaurus, famous as the “bone-headed dinosaur” with a domed skull, Dracorex has a flat head with no dome.
At a glance, they look like different species, but detailed analysis pointed out the following:

All Fossils are “Children”

Dracorex fossils are small in size, indicating a high possibility that they are growing juveniles.

Matching Parts

When comparing the skeleton with Pachycephalosaurus and Stygimoloch from the same era, characteristics other than the horns and dome match perfectly.

From this, a new diagram of “a dinosaur that changes its appearance dramatically as it grows” emerged.

From Dracorex to Pachycephalosaurus: A Dramatic Transformation

Jack Horner’s theory is now well-established, and the three dinosaurs once thought to be independent species are now believed to be different growth stages of a single species, “Pachycephalosaurus.”

If likened to humans, the growth stages are as follows:

Early Teens (Juvenile) = Dracorex

The period when the head is flat, but the horns on the back of the head are growing long and sharp.
This appearance was mistaken for a “dragon.”

Late Teens (Sub-adult) = Stygimoloch

The period when the dome on the top of the head begins to swell, but the horns on the back of the head still remain long.
It used to be called the independent species “Stygimoloch.”

Adult = Pachycephalosaurus

The dome on the head fully grows and becomes massive.
As a trade-off, the horns on the back of the head are absorbed, becoming shorter and rounder.

In short, Dracorex was essentially a nickname given to “Pachycephalosaurus during its childhood.”

Value Remains Even as an Illusion: A Carnivorous Childhood?

As an independent species, “Dracorex” is destined to disappear from taxonomy.
However, its discovery provided extremely valuable evidence.

Detailed examination of the Dracorex skull revealed that sharp triangular teeth resembling those of theropods (carnivorous dinosaurs) grew in the front of the jaw.

It was revealed that sharp triangular teeth resembling those of theropods (carnivorous dinosaurs) were growing.

While adult Pachycephalosaurus are considered fully herbivorous, during their childhood (the Dracorex phase), they may have been omnivorous, eating insects and small animals to ingest high-nutrition food for rapid body growth.

The name “Dragon King of Hogwarts” may become a phantom in academic terms, but the “story of growth” told by its bones has vividly changed our view of dinosaurs, just like magic.