An Omnivorous Dinosaur with Unique Teeth

The most distinctive feature of Alwalkeria was its heterodonty.
While most dinosaurs had teeth of the same shape, Alwalkeria had both straight teeth for eating plants and curved teeth for tearing meat.
This suggests that it was an omnivore, eating both animals and plants.

Scant Fossils and Future Possibilities

The only fossils of Alwalkeria discovered to date are very fragmentary, including the tips of the upper and lower jaws, 28 vertebrae, a femur, and an ankle bone.
Because of this, much about its complete appearance and ecology is still shrouded in mystery.

The well-preserved skull is believed to be from a juvenile. If it were an adult, its height would have only reached a person’s knees.
The scarcity of fossils has also led to debates about its existence and whether it might be the same species as Eoraptor.

An Important North American Discovery Bearing the Name of “Ghost”

Name Origin and Discovery

The scientific name Chindesaurus is derived from “Chinde,” a word meaning “ghost” or “evil spirit” in the language of indigenous people such as the Navajo.
It was discovered by Bryan Small of the University of California in 1984 and formally described in 1995.
Contrary to its terrifying name, their fossils are vital clues telling the history of dinosaur migration.

Nickname: “Gertie”

Actually, this dinosaur has a friendly anecdote that contrasts with its scientific name.
When first discovered, the American media nicknamed this dinosaur “Gertie,” after the classic animated film Gertie the Dinosaur.
Making headlines, they were the center of attention at the time.

From South to North? The First Herrerasaurid in the Northern Hemisphere

Chindesaurus is a carnivorous dinosaur approximately 2.4 meters long, but its classification is its most significant feature.

Proof of Expansion into the Northern Hemisphere

They are a related species (Herrerasauridae) to the early dinosaur “Herrerasaurus,” known from places like Argentina.
Many Herrerasaurids had been found in South America, but there were no prior discovery records in the Northern Hemisphere.
Therefore, Chindesaurus holds extremely high significance as the “first Herrerasaurid discovered in the Northern Hemisphere.”

Mystery of Survival and Migration

Its habitat era is estimated to be approximately 212 million years ago (Late Triassic).
This is a later era than the South American Herrerasaurus (approx. 220 million years ago).
This suggests the possibility that some Herrerasaurids originating in the Southern Hemisphere moved north to North America and continued to survive there.
They are counted among the oldest class of dinosaurs found in North America.

Long Legs and a Whip-Like Tail

Its physical characteristics share many commonalities with early dinosaurs.

Long Hind Limbs

Particularly striking are its very long hind limbs.

Short Torso

In contrast to the long legs, the torso had a relatively short and compact shape.

Tail

It possessed a long tail that was flexible like a whip.

Chindesaurus, an ancient witness telling the story of the great dinosaur migration from South to North.
The “Ghost” found in the wilderness of Arizona conveys to us the dynamic history of how dinosaurs spread across the Earth during the Triassic period.

“Hollow Form” and a Sleek, Swift Runner

Origin of the Scientific Name

The scientific name Coelophysis means “Hollow Form” in Greek.
True to its name, the interiors of their bones were hollow.
This structure, which dramatically reduced weight while maintaining strength, is a characteristic shared with modern birds and served as a vital weapon for their success as agile hunters.

Physical Characteristics

Its total length was about 3 meters.
About the size of Deinonychus, it possessed an extremely slender physique.

It possessed an extremely slender physique

Using its long neck, tail, and powerful hind legs, it is believed to have been capable of running at speeds of 30 km/h.
Additionally, its forelimbs had three fingers equipped with sharp claws, and with over 100 serrated teeth lining its upper and lower jaws, it never let prey escape.

With over 100 serrated teeth lining its jaws, it never let prey escape

The Miracle of Ghost Ranch and the “Rioarribasaurus Incident”

Mass Death of Over 500 Individuals

In 1947, Edwin Colbert discovered a “bone bed” containing fossils of over 500 Coelophysis individuals at “Ghost Ranch” in New Mexico.
It is speculated that an entire herd was swallowed and deposited by a sudden flood. This became a precious discovery that included individuals of various growth stages, from children to adults.

Controversy Over the Scientific Name

This discovery later triggered a controversy known as the “Rioarribasaurus Incident.”
Suspicions arose that the initially discovered holotype and the Ghost Ranch specimens were different species, and for a time, the new name “Rioarribasaurus” was proposed.
However, a solution was ultimately reached to redesignate the Ghost Ranch specimen as the “neotype,” and the name Coelophysis was preserved.

Alleged “Cannibalism” and True Diet

Juvenile Bones in the Stomach?

The most sensational aspect of the Ghost Ranch discovery was the small bones found in the abdominal region of an adult.
Initially, this was taken as evidence that it “ate its own children (cannibalism),” and for a long time, Coelophysis was featured in illustrated books as a “cruel cannibal dinosaur.”

New Discoveries Clearing Its Name

However, recent reanalysis has overturned this established theory.
It was revealed that the bones in the stomach were not juveniles, but rather early crocodylomorphs such as “Hesperosuchus.”
It was not eating its own kind, but merely preying on small crocodile relatives.
After more than half a century, the stigma of “child killer” was finally cleared.

Actual Diet

Using their sharp teeth and agility, they hunted lizards, mammals, and small crocodylomorphs, while also appearing to have a side as scavengers that scavenged the leftovers of large carnivorous dinosaurs.

True to the Name “Dawn Runner”! Speedy Feet Specialized for Escape

Origin and Meaning of the Name

The scientific name “Eocursor” carries the meaning “Dawn Runner.”
True to its name, they possessed high physical abilities specialized for running.

Long Shin Bones = Proof of High-Speed Running

A characteristic of the discovered fossils is that the shin bones are longer than the femurs (thigh bones).
Biologically speaking, this leg structure indicates suitability for high-speed running.

At that time, the best defense for Eocursor against predators like carnivores was not to fight.
It is believed that their survival strategy was to use their long legs to run away at high speeds.

Iguana-like Teeth and Herbivorous Ecology

Leaf-shaped Teeth

Its mouth was lined with “leaf-shaped” teeth.
These teeth closely resemble those of the modern green iguana, telling us that they were adapted to eat plants efficiently.

A small herbivorous dinosaur with iguana-like teeth, dashing like the wind across the land over 200 million years ago.
That is the true image of Eocursor.

The Roots of Ornithopods? An Important Taxonomic Position

Regarding classification, there is a theory that it is not a true ornithopod, but as an early dinosaur, it is certainly positioned close to the evolutionary roots of ornithopods.
Eocursor is positioned as a crucial entity for understanding the origins of the ornithopods that flourished in later eras (such as Iguanodon and Hadrosaurus).

A Refined, Small Hunter! Four Physical Characteristics

Eodromaeus was a very small, lightweight, and slender dinosaur, measuring approximately 1.2 meters in length and weighing only about 5 kilograms.
It ran swiftly on its two long hind legs and skillfully maintained its balance using its long tail.

Its skeleton already clearly possessed the “basic characteristics of a carnivorous dinosaur” that would later be passed down to large theropods such as Tyrannosaurus and Allosaurus.

Sharp Fangs and Serrations

The upper jaw was lined with long, sharp fangs, and the edges featured fine, steak-knife-like serrations.
This indicates that it was a pure carnivore, reliably capable of taking down its prey.

Lightened Bones

Some of its neck bones contained hollow spaces, indicating that its body was lightened to adapt for quick, agile movements.

A Pelvis Unique to Theropods

The tip of the “pubis” extending forward and downward from the hips was slightly expanded, which is also a structure unique to theropods.

Hands that “Primarily Used Three Fingers”

Its forelimbs (hands) had five fingers, but the fourth and fifth fingers were vestigial and extremely small, so only the remaining three were used for hunting and other activities.
While retaining all five fingers on the hand is extremely primitive, the trait of “primarily using three fingers” is a crucial commonality that continues into later theropods.

The History of Research: From Its Discovery in the “Valley of the Moon” to Its Description as a New Species

The reference fossil (holotype specimen) of Eodromaeus was discovered in 1996 in the Ischigualasto Formation, commonly known as the “Valley of the Moon” (Valle de la Luna), a fossil site in the San Juan Province of Argentina.
Ricardo Martinez, a member of the expedition team led by the renowned University of Chicago paleontologist Paul Sereno, excavated the fossil in excellent condition with nearly the entire skeleton articulated.

Following over a decade of detailed comparison and analysis, it was formally described in 2011 in the prestigious scientific journal “Science” as a new genus and species, Eodromaeus murphi.
(*The specific name “murphi” is dedicated to James Murphy, who supported the excavation and research project.)

“Parting Ways with Eoraptor,” Rewriting the Dinosaur Family Tree

The announcement of Eodromaeus had a massive impact on the paleontological community, enough to rewrite the textbooks on dinosaur evolutionary history.
The reason lies in the classification of Eoraptor, a dinosaur that Eodromaeus was mistakenly thought to be identical to when first discovered.

For many years, Eoraptor was considered the “earliest theropod.”
However, as a result of a detailed comparison with Eodromaeus, which was adapted for pure carnivory, decisive differences were found, such as the fact that Eoraptor possessed “heterodont” teeth suitable for both carnivorous and herbivorous diets.

Triggered by this comparative research, Eoraptor was re-examined, and its classification was changed: it was actually not a theropod, but the most primitive member of the “sauropodomorphs,” the group that would eventually lead to the giant long-necked dinosaurs (such as Apatosaurus and Brachiosaurus).

“Two Evolutionary Paths” Diverging at Dawn

The greatest truth revealed by the discovery of Eodromaeus is that right at the “dawn” of the dinosaur age approximately 230 million years ago, the two major groups of dinosaurs—theropods (carnivores) and sauropodomorphs (herbivores)—had already begun to walk entirely different evolutionary paths.

These two small, seemingly similar dinosaurs lived in the same “Valley of the Moon.”
Over an unimaginable span of time, Eodromaeus, which sharpened its blades as a pure carnivore, would undergo ultimate evolution into Tyrannosaurus, while Eoraptor, which began adapting to a plant-based diet, would evolve into Brachiosaurus.

Hidden within the small, delicate body of Eodromaeus is an extremely significant historical value: the starting point of the magnificent drama of dinosaur evolution.

The Quest for the “Oldest Dinosaur”

Fossils of Eoraptor were discovered relatively recently, in 1991.
This discovery provided a massive clue for unraveling how dinosaurs evolved.

While Eoraptor is often considered the “oldest dinosaur,” the quest and debate surrounding this title continue.
The larger Herrerasaurus was discovered in the same geological formation as Eoraptor, and fossils of the supposedly even older Nyasasaurus have been found in Africa.
Because the fossils of Nyasasaurus are fragmentary, opinions are divided on whether it is a “true dinosaur.”

Given this context, Eoraptor holds the highly crucial position of being “one of the oldest living species among those that can definitively be called dinosaurs.”

An Agile Body: Theropod or Sauropodomorph?

Eoraptor was a small dinosaur, roughly the size of a fox, but its long hind legs and lightweight build allowed it to move with great agility.
Standing on its hind legs and using its long tail for balance, it was capable of running quickly.

Following its formal description in 1993, Eoraptor was classified as a theropod, a group of carnivorous dinosaurs.
However, the study of the new dinosaur genus Eodromaeus in 2011 sparked a massive debate over its classification.

Theropod Characteristics

The teeth in the back of its jaw were sharp, a characteristic typical of carnivorous dinosaurs.

Sauropodomorph Characteristics

The teeth at the front of its jaw were leaf-shaped, similar to those of primitive sauropodomorphs.
The shape of its external nostrils and the fingers on its forelimbs also resembled those of sauropodomorphs.

Today, it is increasingly likely that Eoraptor will be classified as an early sauropodomorph.
This debate is significant because Eoraptor’s taxonomic placement is a key to solving the great mystery of “what the common ancestor of all dinosaurs looked like.”

Agile Body and Primitive Features

Eoraptor’s long jaw, complete with sharp teeth, did not possess a strong bite force.
It freely moved its long neck to catch fast-fleeing prey or eat plants such as ferns and cycads.
Its forelimbs had five fingers, three of which were long and equipped with sharp, powerful claws.
It used these claws to pin down prey, grasp plants, and protect itself from enemies.

Eoraptor is also characterized by “heterodonty”—having teeth of different shapes in the front and back of its mouth.
The front teeth were leaf-shaped and suited for a plant-based diet, while the back teeth were curved and suited for a carnivorous diet.
It is believed that by making full use of these teeth and claws, it could prey on animals roughly its own size.

Ecological Mysteries and Fossil Discovery

Eoraptor fossils were discovered in 1991 by a joint expedition team led by Argentine paleontologist Ricardo N. Martínez and Paul Sereno of the University of Chicago.
It took about a year to excavate an almost complete skeleton, and in 1993, it was formally described as a new genus in a scientific paper.
The location where it was discovered is called the “Valley of the Moon,” from which the specific name “lunensis” is derived.

Because no skin fossils have been found, it remains unknown whether it was covered in scales or had feathers.
However, since it lived in a warm region, it might not have needed feathers to keep its body warm.

Eoraptor is a truly fascinating creature, holding the great mysteries of dinosaur evolution within its tiny body.

Name Origin: “True Two Types of Teeth”

The scientific name Eudimorphodon comes from the Greek words for “true (Eu),” “two forms (dimorph),” and “tooth (odon).”
This name derives from the characteristics of the 110 teeth lining its mouth.

Two Types of Teeth with Different Roles

A total of 110 teeth were tightly lined up in its mouth, which measured about 6 cm in length.

A total of 110 teeth were tightly lined up in its mouth

Tip

“Long, pointed fangs” for catching slippery prey.

Back

“Flat teeth” with multiple cusps (serrations).

Because it possessed teeth with clearly different shapes depending on their location, it was crowned with the name “True (heterodont).”

Difference from Dimorphodon

The Jurassic pterosaur “Dimorphodon,” which has a similar name, also possessed two types of teeth, but the shapes of the teeth themselves were basically the same.
A major characteristic of Eudimorphodon is that the roles and shapes were clearly distinct, like fangs and molars. Despite the similarity in names and habitat (Europe), the two are not particularly closely related.

Fish or Crustaceans? Diet Revealed by Worn Teeth

What did they eat using these complex teeth?

Piscivore Theory (Dominant)

The most dominant theory is that they were piscivores (fish-eaters).
Since fish scales have been found in the stomach area and fish fossils have been discovered in the same geological strata, it is believed they caught fish near the surface using their long snouts and sharp front teeth.

Crushing Hard Prey

On the other hand, “wear” was observed on many of the discovered teeth.
Since the biting surfaces were flattened, it is possible they used their back teeth to crush not only fish scales but also prey with hard shells, such as crustaceans.

Earlier than Archaeopteryx! Complete Flight Capabilities

Eudimorphodon lived approximately 210 million years ago.
Although this is long before Archaeopteryx, which is considered the oldest bird, its flight functions were already complete.

Abnormally Long “Fourth Finger” Wings

The “fourth finger (ring finger)” of the forelimb extended abnormally long, forming a wing with a membrane stretched from it.

The fourth finger of the forelimb extended long, forming a wing with a membrane stretched from it.

The wingspan was about 1 meter.
The remaining three fingers had claws, which they could use to climb cliffs or grasp objects.

Long Tail Acting as a Rudder

They had a tail longer than their body, with a diamond-shaped rudder (flap) at the tip.

It had a tail longer than its body, with a diamond-shaped rudder at the tip.

As early pterosaurs, it is believed they used this tail to balance and turn quickly in the air.

Fur and Endothermy

Fossils reveal that they were covered in “fur-like skin,” suggesting they were “endothermic (warm-blooded)” animals capable of maintaining their body temperature.
It was because they had warm blood and a coat that high-energy flight was possible.

Suddenly Appeared in Complete Form: An Evolutionary Mystery

Eudimorphodon appears suddenly in the fossil record during the Late Triassic.
Normally, there should be intermediate stages gradually acquiring wings from “flightless ancestors,” but they are found in a state where “wings and flight capabilities are almost complete.”
Partly because bones are fragile and do not preserve well, definitive ancestral fossils have not been discovered.
They are a precious existence that conveys the “first successful form” of vertebrates advancing into the sky.

An “Old Timer” with a History Longer than Tyrannosaurus

The 1863 Discovery and the Bizarre Scarcity of Fossils

The discovery of this dinosaur dates back to 1863, approximately 200 years ago.
This predates the discovery of the famous Tyrannosaurus (1892), making it a historic figure—effectively a “veteran”—in the field of paleontology.

However, despite this long history, the number of excavated bones remains strangely low to this day, consisting only of limb bones and vertebrae.

Name Recognition in Japan: Countable on Two Hands?

An old discovery, yet few fossils.
Perhaps because of this, it is said to be a very obscure dinosaur that most people in Japan—perhaps only a handful, to be extreme—would not know.
It is a niche existence known only to true enthusiasts.

From Carnivory to Herbivory: Dietary Transition and Evolution

Characteristics as an Intermediate Dinosaur

Prosauropods, the group to which Euskelosaurus belongs, are believed to represent an “intermediate” stage where dinosaurs transitioned from meat-eating to plant-eating.
In fact, the teeth of Euskelosaurus were shaped to handle both animal and plant matter efficiently.

A Body Too Large for Hunting

While the shape of their teeth suggested potential omnivory, their bodies were likely too large to actively attack and hunt prey.
Therefore, it appears they lived primarily on a diet of plants.

“Curved Femur” to Support Large Digestive Organs

A distinct physical characteristic is that the femur (thigh bone) curves outward from the torso.
This is hypothesized to be due to reasons specific to herbivores.

Because plants take longer to digest than meat, a longer intestinal tract is required.
The curvature of the femur may be an evolutionary adaptation of the skeleton to accommodate the massive digestive system needed to process and absorb plant matter within the abdomen.

Relationship with Herrerasaurus: A Different Species or a Fully Grown Form?

The greatest characteristic of Frenguellisaurus lies in the ambiguity of its classification.
This is because it looks extremely similar to the primitive dinosaur “Herrerasaurus” that lived in the same era and region.

The Prevailing “Synonym” Theory

Since many skeletal features match those of Herrerasaurus, many researchers believe that “Frenguellisaurus is merely a fully grown Herrerasaurus.”
If this theory is correct, the scientific name Frenguellisaurus would become invalid and be subsumed into Herrerasaurus.

Grounds for Being a Distinct Species

On the other hand, features that clearly distinguish the two have also been confirmed.
In particular, the structure of the lower jaw and a unique “constriction” are not seen in Herrerasaurus.
Therefore, it is still sometimes treated as an independent species, and the debate over its true identity remains unsettled.

A 6-Meter “Earliest Giant”

Although there are taxonomic debates, it is an undeniable fact that Frenguellisaurus possessed an exceptionally massive body for the Triassic period.

Largest of Its Time

Its estimated total length is about 6 meters.
While small compared to large theropods of later eras, it was an overwhelming “giant” by Late Triassic standards.

• Frenguellisaurus: Approx. 6m
• Herrerasaurus: 3–6m
• Staurikosaurus: Around 2m

In the Ischigualasto Formation where they were found, they boasted a size a cut above the rest and reigned at the top of the ecosystem.
Incidentally, the scientific name means “Frenguelli’s Lizard,” named after the Argentine paleontologist Dr. Joaquín Frenguelli.

The Apex Predator’s Table: Targeting Scaphonyx

As the rulers of that time, what did they eat to maintain their massive bodies?

Main Diet: “Scaphonyx”

Large quantities of “Scaphonyx (rhynchosaurs),” herbivorous reptiles measuring 1 to 3 meters in length, have been found in the geological layers where it was discovered.
It is believed that the slow-moving Scaphonyx was the perfect “staple food” for Frenguellisaurus with its powerful jaws.

Possibility of Piscivory (Fish-Eating)

Additionally, based on the unique “constriction” in the jawbone and the characteristics of its sharp teeth, a theory has been proposed that they preyed on fish at the water’s edge, much like modern crocodiles.

The Kaiju-Loving Paleontologist and His Insistence on “Gojira”

The Namer was a Tokyo-Born Godzilla Fan

Behind the shocking name of Gojirasaurus lies the passion of one paleontologist.
The name was given by the renowned paleontologist Dr. Kenneth Carpenter.
He was actually born in Tokyo, and it is said that watching Godzilla movies in Japan during his childhood left a strong impression on him, eventually inspiring him to pursue the path of paleontology.

For him, Godzilla was a special entity that defined his life.
In 1997, when he discovered that the carnivorous dinosaur he was studying was a predator of exceptional size for its time, he decided without hesitation to crown it with the name of the “King of the Monsters.”

“Gojira,” not “Godzilla”

There is a particular insistence regarding the scientific name.
Instead of the English spelling “Godzilla,” he deliberately adopted the Japanese pronunciation “Gojira,” naming it “Gojirasaurus.”
The spelling of its full scientific name, Gojirasaurus quayi, reflects the doctor’s deep respect for Japanese culture and his cherished childhood memories.

The “Real-Life Godzilla” That Ruled the Triassic Ecosystem

“Largest Class” Size Even as an Immature Individual

Fossils of Gojirasaurus were discovered in New Mexico, USA, in 1981.
Although the specimen found was an “immature individual” still in the process of growing, it was estimated to be about 5.5 meters long and weigh 150–200 kg.
It is believed that a fully grown adult would have reached a length of about 6.5 meters.

To the Top of the Ecosystem

About 220 million years ago (Late Triassic), when they lived, most dinosaurs were still small.
With relatives like Coelophysis (3 meters long) being the mainstream, Gojirasaurus exceeding 6 meters was exceptionally huge.
Given its ferocious nature, there is no doubt that it was one of the largest predators in North America at the time and reigned at the top of the ecosystem.
Like the movie Godzilla, they too were the “Kings” of the Triassic era.

Differences from the Other “Godzillasaurus”

The Intersection of Movie and Reality

In the movie Godzilla vs. King Ghidorah (1991), a fictional dinosaur called “Godzillasaurus” appears as the pre-mutation form of the monster Godzilla.
However, other than the similar name, it is completely different from the real “Gojirasaurus.”

Although their eras and ecologies differ, it is fascinating how the worlds of science and fiction are linked through the legendary icon of “Godzilla.”