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.

The Apex and Largest Species of Nodosauridae

Among armored dinosaurs (ankylosaurians), Edmontonia belongs to a group called the “Nodosauridae” family.
This group followed a different evolutionary path than the famous Ankylosaurus (Ankylosauridae family).

Ankylosauridae

Possessed a hammer (club) at the end of their tail.

Nodosauridae

Did not possess a tail hammer, but instead developed large spikes along their shoulders and flanks.

Edmontonia had the largest body within this Nodosauridae family and was the species to appear in the latest era.
In other words, it can be said to represent the ultimate evolutionary form of this group.

An Impenetrable Defense System: “Massive Spears” Pointing Forward

S-Class Super Armor and Forward-Facing Spikes

Edmontonia’s back was equipped with a formidable super armor (bony armor) described as being “like a heavy tank.”
However, its most defining feature is the array of sharp, massive spikes that lined the sides of its shoulders like a breakwater.

What is particularly noteworthy is that these spikes point “forward.”
While the spikes of many armored dinosaurs face sideways or backward, Edmontonia’s forward-oriented spikes became a powerful weapon with offensive capabilities, rather than just being for defense.

Intimidation and Display

It is believed that these well-developed spikes were used not only to intimidate carnivorous dinosaurs but also for “sexual display” during conflicts among their own kind (such as fighting over mates or territory).
Recent studies have revealed that their strength was not as high as the tail spikes of Stegosaurus, but they still packed enough power to flinch an opponent in close combat.

Battles with Natural Enemies: Anti-Tyrannosaur Tactics

The Attacking “Tyrants of the Dawn”

At the time in North America, ferocious predators that could be called the “tyrannosaurs of the dawn,” such as Albertosaurus and Daspletosaurus, were prowling around, and Edmontonia was a target for them.

A Powerful Counter from a “Prone Position”

While their backs were impenetrable, their abdomens lacked armor and were in an “unguarded state.”
If they were flipped over, it would be fatal.
Therefore, when attacked by an enemy, they employed the following tactics.

Defense

Utilizing their low center of gravity, they would drop down flat on the spot, hiding their vulnerable abdomen against the ground.

Counterattack

If the enemy still attacked, they would surge forward, thrusting their massive, forward-facing spikes out to deliver a powerful blow into their attacker’s legs.

This combined tactic of offense and defense is what wounded the legs of tyrannosaurs and supported their survival.

The Turnover of Three Species and Taxonomic History

A 10-Million-Year Evolutionary Relay

During the final 10 million years of the Cretaceous period, the following three species appeared in succession in North America.

• Edmontonia rugosidens
• Edmontonia longiceps
• Edmontonia schlessmani

The final species, schlessmani, coexisted with star dinosaurs like Ankylosaurus, Tyrannosaurus, and Triceratops, witnessing the end of the dinosaur age.

Shifting Classification and Names

There have been changes in its classification, and for a time, different genus names (Chassternbergia and Denversaurus) were given.
Denversaurus in particular was the subject of a very interesting discussion at a 2015 academic conference, where the view was presented that “it is entirely possible to view it as a separate genus.”

Surprising Mobility and a “Gourmet” Side

A “Heavy Tank” That Wasn’t Slow and Heavy

Despite its heavy appearance, it actually had relatively long legs for an armored dinosaur, and it is thought to have been able to move faster than others of its kind.
This surprising mobility also aided in its survival.

A Gourmet Who Foraged Selectively

Its snout had a relatively narrow shape, making it suited not for indiscriminately eating ground plants, but for selectively eating specific ones.
It is said that they engaged in “selective foraging,” picking and choosing nutritious ferns and young shoots to eat, making them “gourmets” adapted to their environment.

A “Living Tank” Clad in Iron-Clad Armor

A Flawless Defense System

As its nickname suggests, the greatest characteristic of Euoplocephalus was the “hard armor” that completely covered its exterior.
This armor was truly impregnable, further covered by countless horn-like protrusions jutting out from the surface.

Hard armor and countless protrusions completely covering the exterior

The fact that they were able to survive in the Late Cretaceous, a time filled with powerful predators, is entirely due to this perfect defense system.

Furthermore, it is believed that in emergencies, such as when surrounded by enemies, they would crouch flat on the ground to hide their vulnerable, unarmored bellies and wait out the danger.
Just like a tank, they could assume a defensive posture with no gaps.

Differences from Ankylosaurus: Three Toes and Era

Its appearance is the spitting image of the fellow armored dinosaur star, “Ankylosaurus,” but Euoplocephalus lived in a much older era.
There are also unique features in the details of its body.
While many related dinosaur species had four toes, Euoplocephalus had only “three.”
This foot characteristic serves as an important point for distinguishing it from other species.

A One-Hit-Kill Weapon: The “Tail Hammer” That Could Crush Even a Tyrannosaurus

Structure and Power of the Bone Mass

Another symbol of Euoplocephalus is the giant bony mass attached to the tip of its tail.

A giant bony mass attached to the tip of the tail

This mass, formed by several fused bones, is likened to a “mace” or “club.”
Its shape is massive enough to be described as a “Frisbee-like disc-shaped mass.”

Research indicates that while the tail muscles couldn’t move much vertically, they could swing powerfully in a horizontal (side-to-side) direction.
If an adult individual swung this tail with full force, it likely could have shattered the knee bones of even a Tyrannosaurus in a single blow.

Excellent Sense of Smell and a “Picky Eater” Side

A Picky Eater That Preferred Soft Plants

Despite its heavy equipment, Euoplocephalus had a surprisingly small head and small teeth.
Therefore, it couldn’t eat very hard plants and is believed to have selectively eaten soft grasses and flowers.
Contrary to its rugged appearance, its diet seems to have been delicate.

Excellent Sense of Smell Supporting Survival

This diet was supported by its “excellent sense of smell.”
Its keen sense of smell was highly useful not only for finding the soft plants it fed on but also for quickly detecting the approach of natural enemies like carnivorous dinosaurs.

Abundant Fossils and Contribution to Ankylosaurus Reconstruction

Armored dinosaurs are a group where finding fossils in good condition is rare, but Euoplocephalus is an exception.
Over 40 specimens have been found in North America, and since many are well-preserved, it is highly popular among scholars and research is well-advanced.

As a Model for Ankylosaurus

Because the specimens are so complete, they are even used as references for skeletal reconstruction diagrams of other armored dinosaurs.
In fact, since few parts have been discovered even for the famous Ankylosaurus, it is sometimes reconstructed by borrowing (referencing) parts of Euoplocephalus bones.

Its Name Means “Gargoyle Lizard”: Derived from Stone Statues Protecting Churches

If hearing the name Gargoyleosaurus brings medieval European Gothic architecture to mind, you have keen instincts.
This scientific name literally means “Gargoyle Lizard.”

What is a Gargoyle?

Rainspouts (stone statues) shaped like devils or monsters that adorn the roofs of old European churches and cathedrals.

Why was an ancient creature given such a name?
The reason lies in the shape of the discovered skull.
Its unique, rugged shape and atmosphere were reminiscent of the gargoyle statues looking down on the world from church roofs.
Its appearance, revived from ancient strata, evokes a sense of romance, as if a stone monster has come to life.

Overturning Ankylosaur Conventions? A Rare Species from the “Jurassic”

When people hear “armored dinosaurs” (Ankylosauria), many imagine the club-tailed Ankylosaurus that thrived in the Cretaceous.
Indeed, finding them in Jurassic strata is extremely rare.

However, Gargoyleosaurus lived in the “Late Jurassic (approx. 161.2–145.5 million years ago),” much older than the Cretaceous.
Currently, only “two species” of Jurassic ankylosaurs have been found globally, making this a precious specimen.

Belonging to the “Nodosauridae,” the pioneers of armored dinosaurs, their existence provides important clues for understanding how heavy armored dinosaurs originated and evolved.

Miraculous Fossil Discovery: From Skull to Lower Body

Usually, ankylosaur fossils are found in fragmentary states, such as “only ribs or parts of armor,” frustrating researchers.
However, Gargoyleosaurus is very fortunate in terms of specimen quantity.

To date, parts ranging from its distinctive skull to its neck, and even partial lower body bones, have been discovered.
Thanks to these abundant fossils, we can reconstruct the appearance of this “earliest armored dinosaur” in detail.

Primitive Characteristics: “Teeth” Remaining in the Beak

Gargoyleosaurus retains “primitive features” not seen in armored dinosaurs that evolved in later eras.
The most prominent example is the “mouth.”
Their mouth width was somewhat narrower than other species, and they possessed an elongated beak.

Surprisingly, “teeth” still remained in that beak section.

Evolved Ankylosaurs

Teeth in the beak have atrophied and disappeared.

Gargoyleosaurus

Seven teeth grew on each side of the upper and lower beak tips, amounting to a considerable total number of teeth.

Seven teeth grew on each side of the upper and lower beaks.

This is decisive evidence that they were in a transitional period of evolution, making it a point of great academic interest.

Ironclad Yet Lightweight? “Hollow Armor” and Defense System

The total length of Gargoyleosaurus was about 3–4 meters.
While small for a dinosaur, its defensive power should not be underestimated.

Spikes Covering the Body and a Shield on the Hips

It was clad in bony armor from head to tail, featuring symmetrical spikes on the neck and thick, sharp spikes lining its sides.

It was clad in bony armor from head to tail.

Worthy of special mention is the armor around the hips.
Small granular bones were densely packed and fused, covering the hips like “one large shield.”
Its heavily armed appearance resembled a giant version of the modern “thorny devil,” truly making it a walking fortress.

The Secret of its Unexpected “Lightness”

However, their armor held a secret unimaginable from the outside.
The bony plates and spikes covering the body were hollowed out inside, making them “lighter” than they looked.
This is a feature distinct from many other ankylosaurs.

By securing agility with this “hollow armor,” they may have maintained the mobility necessary for a small dinosaur.
It is believed that thanks to this ironclad yet functional defense, the carnivorous dinosaurs of the time could not easily lay a hand on them.

A Gift from Cedar Mountain: The Origin of Its Name and Discovery

The “Rosetta Stone” of Ankylosaur Research

Paleontologist Robert Gaston made tremendous contributions to the discovery and study of Gastonia.
In 1989, the first skull was discovered in the “Cedar Mountain Formation” in Utah.
Generally, ankylosaur fossils tend to disarticulate easily, making them difficult to study, but well-preserved specimens representing about five individual Gastonia have been found.

This is a miraculous number for armored dinosaurs, which typically have a poor fossil record. It provides researchers worldwide with invaluable data, serving as a crucial “Rosetta Stone” for unraveling the mysterious ecology and armor arrangement of ankylosaurs.

An Arsenal on Legs: The “Painful-Looking” Armor and Defense System

Gastonia’s most defining feature is its absolute “heavy armament.”
Its appearance goes beyond mere defense, exuding an aggressive aura.

Giant Shoulder Spikes: The Front Line of Intimidation and Defense

The massive spikes jutting out widely to the left and right from its shoulders are a powerful display of “rejection” against enemies attacking from the front or sides.

Massive spikes jutting out widely to the left and right from its shoulders

If a carnivorous dinosaur tried to bite its throat, the spikes acted as a barrier; if it pounced, it risked being impaled.
This was the first line of defense and functioned as an intense intimidation device.

The Sacral Shield: The Keystone of Absolute Defense

Above its hips was a massive, monolithic bone shield called the “sacral shield.”
This composite armor, formed by the fusion of countless osteoderms (bone plates in the skin), completely covered the “hips”—the greatest weak point of a quadrupedal dinosaur—boasting absolute defensive power that neutralized attacks from behind.

Blade-like Osteoderms on the Tail: A Lethal Counterattack

It lacked the tail club of the famous Ankylosaurus, but instead, “blade-like bone plates” lined both sides of its tail.
The moment a carnivorous dinosaur tried to circle around to its side, a swing of Gastonia’s tail would turn those sharp blades into a slashing counterattack, sweeping the predator’s legs and tearing its flesh.

A Taxonomic Puzzle: A Hybrid of Nodosaurus and Ankylosaurus?

Gastonia sparked taxonomic debates due to its characteristics.

Body

No tail club and spikes on its back (characteristics of the Nodosauridae family).

Head

Broad and nearly trapezoidal in shape (characteristics of the Ankylosauridae family).

Possessing the hybrid features of “the body of a nodosaur and the head of an ankylosaur,” the prevailing theory currently classifies it alongside “Polacanthus“—which shares similar traits—into the family Polacanthidae (or the subfamily Polacanthinae within the family Nodosauridae).

Mortal Combat with Its Arch-Nemesis Utahraptor: The Ultimate Spear vs. The Ultimate Shield

In Utah, where Gastonia lived, there also resided “Utahraptor,” the largest species of dromaeosaur.

Both have been discovered in the same geological formation, proving without a doubt that they coexisted.
Against Utahraptor‘s massive “sickle-like claws,” Gastonia countered with its “impenetrable armor” and “spikes.”
It was an evolutionary arms race between “the ultimate spear (Utahraptor)” and “the ultimate shield (Gastonia)” fought upon the lands of Cedar Mountain.
Gastonia’s excessive, heavy armament may have evolved precisely because of the existence of this formidable natural enemy.

Moving Fortresses in a Herd

Gastonia fossils are sometimes found in “bonebeds,” where multiple individuals are discovered together in the same location.
This is strong evidence that they lived in herds rather than solitary lives.
The sight of heavily armored, spike-covered tanks moving together in a herd must have been breathtaking.
Even for Utahraptor, it must have been impossible to attack a tightly packed herd of fortresses.

The “Third Dinosaur” Etched in History and Mantell

The greatest feature of Hylaeosaurus lies not in its biological ecology, but in the history of its discovery and research.

Naming by Gideon Mantell

This dinosaur was discovered and named by Gideon Mantell, who is also famous as the discoverer of Iguanodon.
The scientific name means “Forest Lizard.”
It is recorded as the third dinosaur in the world to be given a scientific name, following Megalosaurus and Iguanodon.

The Three Species Used to Define “Dinosauria”

Even more important is Richard Owen’s definition of “dinosaurs.”
When Owen first proposed the classification group “Dinosauria,” he cited Megalosaurus, Iguanodon, and this Hylaeosaurus as his basis.
In other words, it is a monumental existence; without it, the establishment of the word and concept of “dinosaur” might have been delayed further.

Ironclad Defense! Armor of Spikes and Bony Plates

Hylaeosaurus is a medium-sized herbivorous dinosaur, 4 to 6 meters in length, classified in the same group of “armored dinosaurs (Ankylosauria)” as Ankylosaurus.
Unfortunately, the skull has not been found, and discovered fossils are only of the front half of the body, but the remaining skeleton reveals its appearance.

Irregular Bony Plates and Hollow Bones

They wore strong armor to protect themselves.
Circular and oval bony plates were arranged irregularly on the neck, shoulders, and back, and hollow bone fragments lined the back.

Giant Spikes on the Shoulders

Even more distinctive are the large spikes projecting horizontally from the shoulder area.
It is thought that they used these to intimidate predators like carnivorous dinosaurs or to counterattack.

A “Pitiful Dinosaur” Known Only to a Few?

Despite being such an important dinosaur, Hylaeosaurus is also a somewhat overshadowed existence.

Low Recognition and the Polacanthus Theory

Among the three species that can be called the founders of “dinosaurs,” Megalosaurus and Iguanodon are very famous, but Hylaeosaurus takes a step back in terms of recognition.
It is sometimes called a “pitiful dinosaur” known only to enthusiasts.
Also, a theory has been proposed that it might be the same creature as the related armored dinosaur “Polacanthus,” and debate continues among researchers regarding its classification and true identity.

“Spiked Lizard”: Armed as a Full-Body Weapon

Gradation from Plates to Spikes

The scientific name Kentrosaurus means “Spiked Lizard” in Greek.
While the back of Stegosaurus features “pentagonal plates,” Kentrosaurus transitions from small plates on the neck and back to long, sharp “spikes” from the hips backward.

It transitions from small plates on the neck and back to long, sharp “spikes” from the hips backward.

The Mysterious “Shoulder Spikes”

Its most distinctive feature is the pair of long spikes protruding straight out from the shoulders.

A pair of long spikes protruding straight out from the shoulders

While there was once a theory they were on the hips, the established theory today, based on research of related species (such as Tuojiangosaurus), is that they were “on the shoulders.”
The confusion regarding this position is related to the loss of fossils described later.

The Deadly “Thagomizer”

Its greatest weapon was its flexible and powerful tail.
The tip had sharp spikes (thagomizer), and by swinging this like a whip, it served as a powerful defensive weapon against predators like Allosaurus.

It used its flexible and powerful tail as a defensive weapon

A Body the Size of a “Compact Car” and the Diet of a Picky Eater

Size Difference from Stegosaurus

Compared to Stegosaurus (approx. 9m long), Kentrosaurus was quite small, with a length of 2.5–5 meters (average 3–4 meters).
In modern terms, it was about the size of a “compact car.”
However, its compact body was packed with muscle, and spike attacks from a low posture were a threat.

Did It Only Eat Soft Grass?

Its snout was beak-shaped, and it had only seven protrusions for back teeth.
It was poor at crushing hard plants and is speculated to have been a picky eater that preferred “soft plants” like ferns near the ground.

It was a picky eater that preferred plants near the ground

Also, it could not stand up on two legs and grazed quietly on all fours.

New Discovery in 2011: Differences Between Males and Females

Research on femurs in 2011 revealed two types: a “slender type” and a “robust type.”
This is likely a difference between males and females (sexual dimorphism), and it is thought that males, who needed to support their weight during mating, were the “robust type.”

Memories of Pangea and the German Expedition Team

Witnesses to Continental Drift

The existence of Stegosaurus in North America and Kentrosaurus in Africa tells the story of the breakup of the supercontinent “Pangea,” where the continents were once one, and their unique evolution in each location.

The Great Excavation of Tendaguru

In 1909, a German expedition team conducted a large-scale excavation in the Tendaguru Formation of what was then German East Africa (Tanzania).
This survey uncovered a massive number of fossils—hundreds of bones representing about 70 individuals—and it was formally described as “Kentrosaurus” in 1915.

The “Holotype” Lost to War: The Tragedy of Berlin

The fossils transported from Tanzania to the Museum für Naturkunde in Berlin culminated in a magnificent exhibit.
However, that glory did not last long.

The 1943 Berlin Air Raids

During World War II, the museum was bombed and burned down.
Most of the stored Kentrosaurus fossils were destroyed to smithereens.
In particular, the loss of the “holotype” (the standard specimen for the species) was a major academic blow, and much accurate skeletal information was lost forever.

Rebirth from the Rubble

The figure we see today is a reconstruction combining the few parts that survived the bombing, pre-war records and sketches, and bones from other individuals.
Controversies like the position of the shoulder spikes stem from the fact that good-condition fossils were lost in the war.
Researchers are picking up the truth from the rubble to bring the appearance of this dinosaur back to life in the modern age.

Palm-Sized! The Fossils Found Were “Babies”

The fossils of Liaoningosaurus discovered to date share a certain commonality.

Total Length of Only 30 cm

The fossils found measure only about 31 to 34 cm in length.
Due to the lack of fusion in the spine, these are believed to be fossils of “babies (juveniles)” rather than adults (there is also a theory that they are juveniles of the closely related Chuanqilong).
However, the wonders of evolution were condensed within this tiny body.

The Mystery of Armor Protecting the “Belly” Instead of the Back

Typical armored dinosaurs (such as Ankylosaurus) developed sturdy armor on their backs to protect themselves from external enemies like Tyrannosaurus.
However, Liaoningosaurus underwent the exact opposite evolution.

Protecting the Abdomen, Usually a Weak Point

They developed sturdy armor on their “ventral side (belly)” rather than on their backs.
Why was it necessary to prioritize protecting the belly, which would be a weak point for normal armored dinosaurs? The reason lay hidden in their lifestyle.

Overturning Established Theories! “Aquatic Life” and “Piscivory”

The key to solving the mystery of the belly armor lies in the fact that they lived in the water, not on land.

Turtle-like Aquatic Life

Based on features such as the structure of the hip joints and the long claws on the limbs, it has been determined that Liaoningosaurus highly likely led an “aquatic life” much like a turtle.
The mysterious “belly armor” is thought to have been an adaptation to prevent attacks from below while swimming, or to protect the abdomen from injury against rocks on the water bottom.

Armored Dinosaurs Were Not Just Herbivores?

Even more shocking was the discovery of “large quantities of fish fossils” within the abdominal cavity.
Until then, the established theory was that “all ankylosaurs were herbivores,” but this discovery proved that they (at least the juveniles) were carnivores that ate fish, or omnivores.
They likely swam around like turtles in the water, preying on fish using their sharp claws and beaks.