Ankylosaurus

About Ankylosaurus

A Famous Yet Mysterious "Living Fortress"

Ankylosaurus is one of the most famous armored dinosaurs that adorned the end of the Cretaceous period. Its name means "fused lizard," derived from the fact that the sturdy armor plates covering its skull and body were complexly fused and hardened.

However, despite its overwhelming popularity, surprisingly, **not a single perfectly complete skeleton has ever been found.** The appearance of Ankylosaurus as we know it is reconstructed based on fragmentary fossils such as the skull, armor, and tail hammer, as well as by referencing closely related dinosaurs.

For many years, Ankylosaurus had the image of "a slow-moving reptile that simply wore heavy armor to protect itself from carnivorous dinosaurs." However, thanks to recent high-resolution CT scanning technology and biomechanical simulations using computers, this stereotype is being overturned. Let's look at the true appearance of the highly evolved Ankylosaurus revealed by the latest research.

Complex Nasal Structure: A "Heat Exchanger"

For a giant armored dinosaur weighing up to 8 tons, there was an enemy more terrifying than carnivorous dinosaurs. It was "internal body heat." A body covered in thick armor makes it difficult for heat to escape, and there was always a danger that the relatively small brain could suffer from "heatstroke (overheating)" due to the heat generated by the massive body and direct sunlight.

To combat this life-threatening problem, Ankylosaurs evolved an amazing solution. CT scans of the skull revealed that the space continuing from the nostrils (nasal cavity) was **complexly twisted and looped like a "crazy straw."**

In the past, this complex space was thought to be a "resonating chamber for making loud calls." However, recent fluid dynamics simulations have revealed that it functioned as an ultra-high-performance "heat exchanger (air conditioner)." As inhaled air passes through the long tube, it takes heat from the walls where blood vessels gather, rapidly cooling the blood. It is believed that this cooled blood was sent to the brain to protect it from heat.

Ankylosaurus's Diet and Foraging Strategy Revealed by Its Teeth

Ankylosaurus primarily ate ferns and angiosperms (flowering plants) growing low to the ground. Its snout was wide and flat like a shovel, and it is estimated that it indiscriminately harvested and ate about 60 kg of plants a day.

Surprisingly, despite their giant bodies, their "teeth" were very small, and the upper jaw teeth were less than 2% of the skull length. However, a recent analysis of the microscopic scratches (microwear) left on the surface of these small teeth revealed that Ankylosaurs did not just open and close their mouths up and down, but **ground plants with complex movements**, pulling their jaws back after closing them.

Giant Tongue and "Soil Digging" Behavior

Even more interestingly, sturdy "tongue bones (hyoid bones)" have been found in Ankylosaurs. This indicates the possibility that, like modern giraffes, they extended long, flexible, muscular tongues to wrap around plants.

In addition, Ankylosaurus's nostrils faced "downward" rather than forward. Due to this unique structure and sturdy snout, it is thought that they routinely engaged in a behavior called "rooting," where they scrounged through fallen leaves like wild boars or vigorously dug up the soil to eat highly nutritious plant roots and tubers. The downward-facing nostrils can be considered a perfect structure evolved to prevent sand from entering when digging in the soil.

The Tail Hammer: Evolutionary Process and Latest Hypotheses

Ankylosaurus's biggest trademark is the giant bone mass at the tip of its tail, commonly known as the "tail club." Actually, this hammer was not fully formed from the beginning. Tracing the fossil record reveals that first, the tail bones fused to evolve a hard "handle," and then a heavy "knob" was added to the tip tens of millions of years later. If they swung a heavy mass while the handle was still soft, their own tail would break, so this was a logical evolutionary sequence.

Latest Hypothesis: A "Weapon for Dueling" Among Rivals

This hammer had tremendous destructive power, enough to shatter the leg bones of a Tyrannosaurus. Because of this, it was long believed to be a "defensive weapon to protect against carnivorous dinosaurs."

However, in recent years, a major discovery overturned this common sense. When examining well-preserved fossils of a closely related species (Zuul crurivastator), several "healed bone fracture marks" were found on the armor plates of the hips. Analyzing the pattern of the wounds, they did not match bite marks from carnivorous dinosaurs, but **perfectly matched "blunt force damage" caused by a hammer swung by another Ankylosaur colliding from the side.**

Based on this conclusive evidence, the most prominent new theory today is that the tail hammer evolved and was used not so much for defense against carnivorous dinosaurs, but as a **weapon for fighting over territory or mates among members of the same species (intraspecific combat).** They were not simply docile creatures merely defending themselves, but lived dynamic lives fiercely clashing with rivals.

A Dinosaur That Sang Like a Bird? Latest Research on Vocal Communication

"What kind of sound did dinosaurs make?" This has been a long-standing mystery in paleontology. Because soft tissues like vocal cords rarely remain as fossils, it was previously thought that they could only produce a "hissing" breath sound or a low growl with their mouths closed, using reptiles like crocodiles as a reference.

However, in 2023, a **"larynx (an organ involved in vocalization)"** was discovered from a fossil of "Pinacosaurus," a close relative of Ankylosaurus, making it the first time for a non-avian dinosaur. Surprisingly, the structure of the throat bone was much more similar to the organ of modern "birds" than reptiles like crocodiles, and it was designed to move well.

This discovery strongly suggests the possibility that Ankylosaurs **communicated using complex voices**, changing pitch, volume, and tone like birds, rather than simple growls. Covered in thick armor and living in a low posture, they could not show off with flashy dances. It is believed that this bird-like "voice" played a very important role in calling out to distant companions in deep forests or wide plains, intimidating rivals, or singing courtship songs.

History of Discovery and the Misidentification of "Dynamosaurus"

The first Ankylosaurus fossil in human history was discovered in 1900. The prominent paleontologist Barnum Brown discovered more than 70 irregularly shaped bone plates (armor plates).

Interestingly, at the time, it was mistakenly thought that this armor belonged to a giant carnivorous dinosaur found alongside it, and it was announced as a new species of carnivorous dinosaur called "Dynamosaurus." Later research corrected this, clarifying that Dynamosaurus was actually Tyrannosaurus, and the armor plates belonged to a different herbivorous dinosaur (later Ankylosaurus). In fact, the armor plates found at this time preserve **vivid bite marks likely made by a Tyrannosaurus**, serving as valuable evidence of the fierce struggle for survival at the time.

Later, in 1906, another expedition team led by Barnum Brown discovered a fossil (holotype specimen) including a skull and numerous armor plates, and it was officially named "Ankylosaurus" in a 1908 paper. Incidentally, the 1908 reconstruction drawing above does not depict the tail hammer. The hammer fossil was discovered for the first time and additionally reported two years later, in 1910.

Geological Distribution and Major Fossil Specimen Groups

Ankylosaurus fossils have only been found in specific strata in western North America. All of them are from strata just before the mass extinction at the end of the Cretaceous period (about 70 to 66 million years ago), making it one of the dinosaurs that survived until the very last days of the dinosaur era. As for the reason why complete skeletons are not found, it is thought that because they lived in relatively dry inland environments rather than riverbanks, they had fewer opportunities to be buried in sediment after death and become fossils.

The "Godzilla" Movie Series - "Anguirus"

Ankylosaurus also served as the model for the monster "Anguirus," which appears in the "Godzilla" movie series. In the movie's setting, Anguirus is an Ankylosaurus that was enlarged and resurrected by a hydrogen bomb test. Debuting in the 1955 movie "Godzilla Raids Again," it holds a special place in the series' history as "the first monster Godzilla fought on screen."

Initially appearing as an enemy of Godzilla, it is also important to fans that in the later Showa series, it reappeared as Godzilla's reliable "partner and ally," transforming into a character that fought together for the peace of the Earth. While the actual Ankylosaurus was about 6-8 meters long, the first Anguirus to appear in the Godzilla series reached a length of 100 meters.

Ankylosaurus Stamp & Fossil Gallery