A Scientific Name with a Storied Fate

This dinosaur was once known by the name Ingenia.
It was described in 1981, named after the Mongolian place where it was discovered, but it was later found that the genus name had already been used for a type of nematode (roundworm).
Because the International Code of Zoological Nomenclature dictates that a species must have a unique scientific name, the original genus name could no longer be used.
As a result, it followed the unusual path of being renamed to its current genus, Ajancingenia, in 2013, 32 years after its discovery.

Distinctive Body and Adaptation to the Desert

Ajancingenia was small, about 1.8m in length, and belonged to a group of oviraptorids that had a relatively small or absent crest.

Habitat

The fossil was discovered in the Barun Goyot Formation in Mongolia, suggesting it was adapted to live in a harsh, semi-arid, desert-like environment with dunes and rivers.

Skeleton

Compared to other oviraptorids, it had robust, short forearms. Its skeleton was lightweight for its overall size, suggesting it was capable of agile movements.

Gigantic Thumb and Enigmatic Diet

The ecology of Ajancingenia is believed to have been omnivorous, based on its unique forelimbs and jaw structure.

Gigantic Thumb

The bone at the tip of its first digit (thumb) was very large, approximately twice the length of the second finger.
This sturdy thumb is thought to have been used to dig for subterranean prey or plant roots, or to crack hard nuts and shells.

Jaws and Mouth

Its head was very short, and its jaws were deeply curved.
Instead of teeth, its toothless beak had bony projections on both the upper and lower jaws.
This is a characteristic suggesting it ate and crushed fairly hard materials like the shells of shellfish.

Reproduction Secret

A fossil of its nest has been discovered, revealing its egg-laying strategy.
The eggs were laid in pairs, arranged helically in three layers, totaling about 24 eggs.

The unique jaw and nesting evidence of Ajancingenia show how oviraptorids adapted to diverse environments and survived the harsh desert conditions.

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.

Physical Characteristics and Ecology

Archaeornithomimus had an ostrich-like slender body and slim, powerful legs.

It had an ostrich-like slender body and slim, powerful legs.

Because its skeleton was lightweight, it is believed to have been able to run quickly across the ground, just as its agile appearance would suggest.

Its head was relatively small, with large eyes, and its mouth was a toothless, beak-like structure.
Regarding its diet, it is presumed to have been an omnivore that didn’t specialize in one type of food, likely eating plants, insects, and small animals like lizards.

Classification Confusion and “Nomen Dubium”

The classification of Archaeornithomimus has been filled with much mystery and confusion, from its initial discovery to the present day.

Origin of the Name and Primitive Features

As its name suggests, it was initially considered an ancestral relative of Ornithomimus.
However, its features show some slightly primitive aspects.
For example, the first finger (digit I) of its forelimb was short, which was a trait different from other members of the Ornithomimus group.

Not the “Oldest”?

Although its name includes “ancient,” the existence of Pelecanimimus (which lived much earlier) means it cannot be definitively stated that Archaeornithomimus was the direct ancestor of the ornithomimids.

Current Status as a “Nomen Dubium” (Doubtful Name)

The biggest problem with Archaeornithomimus is that the fossils discovered are extremely fragmentary.
Only a few fossils, such as foot bones and parts of the spine, have been found.
Because of this, it lacks the unique, distinguishing features necessary to clearly separate it from other ornithomimid dinosaurs, and many paleontologists doubt whether this genus is a valid taxonomic group.
Such a name is called a nomen dubium (doubtful name), and it has not been concluded whether the name Archaeornithomimus truly represents a valid, distinct species.

Latest Classification Theory (Deinocheirid Theory)

This classification mystery deepens even further.
Read More According to recent research, it is speculated that Archaeornithomimus was not an ornithomimid, but rather a relative of Deinocheirus.
If this theory is correct, it might be more accurate to call it “Archaeodeinocheirus.”

Habitat

The Iren Dabasu Formation, where the Archaeornithomimus fossil was found, was a lush floodplain dotted with rivers and lakes at the time.
This environment was home to a wide variety of dinosaurs, such as the giant ornithomimosaur Gigantoraptor, hadrosaurids, and tyrannosaurids, and it is believed Archaeornithomimus coexisted with them.

Archaeornithomimus is a dinosaur full of mysteries.
The discovery of more complete fossils in the future is awaited to clarify its true appearance and classification.

Distinctive Head and Incredible Speed

Avimimus is known for having a small, rounded head and a very large brain.
It is believed to have had a mechanism to protect its high intelligence, and with its very large eyes, it is thought to have survived the dog-eat-dog world by using these features as weapons.

Furthermore, its neck and hind legs were very long, and its long hind legs, in particular, rank it among the fastest dinosaurs.
It likely used its speed to run across semi-arid regions and catch prey.
Its lightweight body is also thought to have contributed to this speed.

Diet and the Mystery of Feathers

Avimimus had a sharp, sturdy beak instead of teeth.
While it was initially believed to be toothless, like birds, recent research has found that it had a few very small teeth in the back of its beak.
It is thought to have primarily eaten plants, but it may have also eaten small animals, suggesting an omnivorous diet.

It is also known to have had feathers, but it is believed that it could not fly.
The feathers of Avimimus may have been used for thermoregulation or for display (such as mating rituals).

With its unique appearance and high intelligence, Avimimus was truly a “bird-like dinosaur” that lived a tough life in its ecosystem.

The Shock of 1998: A “Missing Link” Supporting Evolutionary Theory

Discovery in the Jehol Biota, China

The story begins in 1998 in the “Jehol Biota” of Liaoning Province, China, famous for its exceptionally well-preserved fossils.
Buried in volcanic ash and miraculously preserved, the fossils of Caudipteryx retained not only the skeleton but also “clear traces of feathers.”

At the time, definitive proof was sought for the theory that “birds evolved from dinosaurs.”
The appearance of Caudipteryx served as “living proof” (a missing link) strongly supporting the hypothesis that “birds evolved from feathered theropods,” delivering an impact significant enough to rewrite textbooks.

The Misconception of the “Flightless Bird”

However, because its appearance was so bird-like (1 meter length, wing-like feathers, short tail), a misconception initially arose: “Could it be a bird that lost the ability to fly after evolving (a flightless bird)?”
Because of its “complete” appearance, Caudipteryx found itself at the center of a controversy regarding its identity.

Dinosaur? Or Bird? The Great Debate

Fluctuating Classification and the Existence of the “Furcula”

One basis for the debate was the development of the “furcula” (wishbone), which connects the muscles used for flight in modern birds.
Possessing this meant they were positioned extremely close to birds.

The Keys to the Conclusion: “Teeth” and “Skeleton”

However, detailed research settled the controversy.

Presence of Teeth

There were clear “small teeth” deep inside its beak-like mouth, retaining reptilian characteristics.

There were “small teeth” deep inside its beak-like mouth

Skeletal Structure

It was determined that the arm proportions and pelvic structure were closer to theropod dinosaurs like “Oviraptor” than to birds.

Today, the established theory is that Caudipteryx is “a feathered oviraptorosaurian theropod dinosaur, distinct from the lineage that evolved into birds.”

Flightless Wings and the Role of Feathers: The “Color” Revealed by Latest Research

Wings as Parachutes

The feathers on its forelimbs were about 20 cm long, but they lacked the “asymmetrical” shape needed to generate lift for flight, and its arms were too short.
However, they were not useless.
It is believed they played a role in increasing air resistance when jumping from trees, softening the impact of falls like a parachute.

Courtship Displays and “Iridescent” Feathers

In addition to insulation, it is highly likely the feathers were used for displays (courtship behavior), spreading the tail feathers to appeal to the opposite sex.
Furthermore, a 2019 analysis of pigment cells (melanosomes) suggested that while their feathers were black-based, they may have possessed an “iridescent” sheen.

It was suggested that the feathers might have had an “iridescent” sheen

In the forests of the Cretaceous, they may have performed courtship dances with feathers shimmering in rainbow colors, much like crows or jewel beetles.

A Small Beast? “Omnivorous Diet” Revealed by Gastroliths

Swift Runner

The skeleton was lightweight, and it possessed developed legs like a bird.

The skeleton was lightweight, and it possessed developed legs like a bird.

Instead of flying with wings, they were “swift runners” that dashed across the land using powerful leg strength.

Gastroliths and Dietary Changes

Initially, it was thought to be carnivorous due to its sharp teeth, but a large number of “gastroliths” (small stones that aid digestion) were discovered inside its stomach.
This is evidence that it ate hard-to-digest plants.
It is highly likely that it was an “omnivore” adapted to its environment, preying on insects and lizards with its sharp teeth while also eating nuts and leaves using the gastroliths.

Was the Real Identity of “Oviraptor” Actually Citipati?

Even if the name Citipati doesn’t ring a bell, you may have seen “a reconstruction of Oviraptor brooding eggs on a nest.”
In fact, the model for that famous reconstruction is actually Citipati.

Discovery and Misunderstanding in the 1990s

In the 1990s, fossils of an oviraptorosaur in a posture covering a nest were discovered in Mongolia.
Fossils of babies were also found inside the eggs, making it famous as a “gentle dinosaur that broods its eggs.”
At the time, this fossil was thought to be a “species of Oviraptor” and was widely introduced as such.

Reclassification in 2001

However, detailed research in 2001 gave this dinosaur the new scientific name “Citipati osmolskae.”
This revealed the following facts:

• The “nest-protecting individual” discovered in the 90s was Citipati.
• The “complete Oviraptor skeleton” reported in 1981 was also actually Citipati.

Many of the famous specimens once thought to be Oviraptor are now reclassified as Citipati.

The Name “Lord of the Funeral Pyre” and a Bird-like Appearance

Origin of the Name

The scientific name Citipati means “Lord of the Funeral Pyre” in Sanskrit.
Although it is a somewhat terrifying name, its appearance was very bird-like.

Features of the Beak and Crest

Belonging to the oviraptorosaurs, Citipati was one of the largest dinosaurs in the group until the discovery of Gigantoraptor.

Feathers

The body was covered in short, fibrous, primitive feathers that maintained body temperature.

Crest

The head had a crest similar to that of a hornbill or cassowary, and it is speculated that it was brightly colored in living individuals and used for display.

Beak

It had no teeth but possessed a sturdy, short beak.

It possessed a sturdy, short beak

“Brooding” Revealed by Fossils: Evidence of Evolution into Birds

Citipati’s greatest characteristic is its “brooding style.”
Fossils have been found sitting on top of their nests with their forelimbs and hindlimbs folded.

Wrapping Eggs with Wings

Of particular note is the “posture covering eggs with spread forelimbs.”
This suggests that they spread the long flight feathers on their arms to wrap around the eggs, protecting them from the elements and keeping them warm.
The behavior of spreading wings to warm eggs is a characteristic seen only in modern birds, serving as strong evidence that Citipati had behavioral patterns very close to birds.
*The eggs were large, with a major axis of about 18 cm.

Additionally, oviraptorosaur eggshell fossils have also been found in Tamba City, Hyogo Prefecture, Japan, indicating that this group was distributed over a wide area.

The Mystery of Diet and “Foreign Objects” in the Nest

Egg Thief? Or Omnivore?

There is no clear conclusion regarding Citipati’s diet.
Although they belong to a group named “egg thieves” (Oviraptoridae), there is no evidence that they regularly ate eggs.
They may have used their powerful beaks to crack eggs, or they may have been omnivores eating plants and small animals.

A Stranger’s Baby in the Nest…

Mysteriously, fossils of two “theropod babies that are not Citipati” were found in a Citipati nest in Mongolia.
There are two theories for this:

Food Theory

The parents brought them back as food to feed their own children.

Brood Parasitism Theory

Like a cuckoo, another dinosaur laid its eggs in the Citipati nest.

Contrary to the name “Lord of the Funeral Pyre,” Citipati gently embraced its eggs with wing-like arms, trying to sustain life in the harsh desert environment.
Its fossils tell the story of the evolution from dinosaurs to birds and the affection of ancient parents.

No Crest? The Misconception of Being an “Oviraptor Juvenile”

Conchoraptor looked very similar to its close relative, Oviraptor.
However, there was one crucial difference.
It completely lacked the showy head “crest” seen in Oviraptor and its relatives.

Thought to Be Juveniles or Females

Because they lacked a crest and were small in size, when they were first discovered, they were thought to be “juveniles of Oviraptor whose crests had not yet fully grown, or perhaps females.”

Identified as a Distinct New Species

Subsequent investigation and research revealed that these were fully grown adults, and they were recognized as a distinct new species of dinosaur with unique characteristics separate from Oviraptor.

They were characterized by an overall slender build, with short and slender fingers on their forelimbs.
Furthermore, a “nearly complete skull” has been discovered, which is rare for this group.
This skull has a highly “pneumatic” structure with many air spaces (cavities), indicating that sensory organs such as hearing and smell were extraordinarily well-developed.

The Origin of the Name “Conch Thief” and Its Powerful Jaw

Why was the seemingly delicate Conchoraptor given a scientific name meaning “conch thief”?
The answer lies in the anatomical structure around its mouth.

A Powerful Jaw for Crushing Shells

Oviraptorosaurs possess hard, nutcracker-like beaks and strong bony projections on their upper jaws.
It is believed that thick, powerful muscles passed through the cavities of Conchoraptor’s skull, giving it a surprisingly strong bite force.

Nostrils Positioned High on the Snout

It also had the characteristic of having its nostrils located rather high on its face.

Based on these three features—the “strong jaw,” “hard projections inside the mouth,” and “high-positioned nostrils”—it was speculated that it “plunged its face into the water to catch mollusks from the bottom, crushing their hard shells with its powerful jaws to eat them.” Thus, it was named the “conch thief” for allegedly stealing and eating shells.
*In reality, it is thought to have been omnivorous, eating not only mollusks but also nuts, insects, and eggs.

The Dishonorable Background of Being Treated as a Thief and the Truth of Being a “Loving Parent”

Actually, the existence of its close relative, Oviraptor, played a major role in it being named a “thief.”

Collateral Damage in Naming

The scientific name of Oviraptor means “egg thief.”
Because its first fossil was found near another dinosaur’s eggs, it was suspected of being a “thief that stole and ate eggs.”
Conchoraptor was named during a time when Oviraptor was still widely considered a thief, so it ended up being named following the logic: “If Oviraptor is an egg thief, then this guy is a conch thief.”

Actually a “Loving Parent”

However, later research found baby dinosaur fossils inside the eggs discovered with Oviraptor, revealing that it wasn’t stealing the eggs at all, but was instead a “gentle parent incubating and protecting the eggs in its own nest.”

Conchoraptor is similarly believed to have had the habit of brooding eggs in a nest, and it is often reconstructed looking like a mother bird protecting her clutch.
Today, its name has been completely cleared of any suspicion of thievery, but because of the taxonomic rule that “a scientific name cannot be changed once established,” it continues to bear this infamous title to this day.

Evidence Revealing the Evolution from Dinosaurs to Birds

It is known that Conchoraptor and some of its close relatives had “feathers.”
The presence of these feathers, along with the habit of “building nests and brooding eggs to keep them warm,” are behaviors shared directly with modern birds.

These discoveries serve as highly compelling evidence supporting the theory that “some carnivorous dinosaurs (theropods) evolved into the ancestors of birds.”
This small dinosaur with a dishonorable name is an important figure that teaches us the grand history of life: that the dinosaurs of the past did not go completely extinct, but rather transformed into birds and continue to live right alongside us today.

The History of Its Discovery and Naming

The fossil of Corythoraptor was discovered at a construction site near the Ganzhou Railway Station in Jiangxi Province.

The discovered holotype specimen was in remarkably good condition, consisting of a nearly complete skeleton missing only a few bones, and is currently housed at the Jinzhou Paleontological Museum.

Its genus name means “Corinthian helmet thief,” representing the presence of the well-developed crest on its head.
Additionally, the specific name “jacobsi” was named in honor of vertebrate paleontologist Dr. Louis L. Jacobs, who served as a mentor to the researchers and as a visiting professor at the Hokkaido University Museum.

Its Greatest Feature! A Cassowary-like “Crest”

The most eye-catching feature of Corythoraptor is the tall “crest” (casque) towering atop its head.

It closely resembles the crest of the modern flightless “cassowary” bird, making it a classic example of “convergent evolution”—a phenomenon where completely different lineages of organisms adapt to similar environments or purposes and develop similar physical traits.

A Lightweight and Flexible Structure

It was only about 2 mm (0.08 inches) thick, and its surface is thought to have been covered in hard keratin.
Its interior was even more “pneumatized” (hollowed out with air pockets) than a cassowary’s, divided into tiny chambers.
While extremely lightweight and flexible, it is presumed that it could not withstand physical impacts such as headbutting.

The Role of the Crest

Although its specific role has not been completely unraveled, it is believed to have been used for multiple purposes much like the cassowary’s, such as “a display for attracting mates and individual recognition” and “thermoregulation (acting as a radiator) for dissipating heat through blood vessels.”

Physical Characteristics of the Head and Skeleton

It was a relatively small dinosaur, measuring about 1.5 meters (4.9 feet) in length, and possessed the anatomical structures typical of the Oviraptoridae family.

Skull and Beak

It had absolutely no teeth, and the presence of foramina (tiny holes for blood vessels) suggests that a keratinous “beak” covered its entire snout.

Cervical Vertebrae and Torso

Its neck bones featured depressions, and parts of its spine were pneumatized (hollowed out) to reduce weight.

Forelimbs (Arms and Hands)

The bones of its arms had gaps between them due to their curvature, and its fingers were equipped with weakly curved claws.

Hind Limbs (Legs)

Its tibia (shin bone) was longer than its femur (thigh bone), and it possessed well-developed feet.

Astonishing Diversity! Ecology and Natural Enemies in Ganzhou

Based on the shape of its beak, its diet is thought to have been either “herbivorous” or “omnivorous.”
Its close relatives include Huanansaurus, Citipati, and Oviraptor.

Interestingly, the Ganzhou region in southern China where its fossils were found was a place where the Oviraptoridae family boasted extremely high diversity, with at least seven distinct genera confirmed, including Corythoraptor.
Because so many closely related species coexisted in a relatively narrow area, it is highly likely that they finely partitioned their ecological niches by altering their diets and specific habitats.

Furthermore, the tyrannosaurid Qianzhousaurus, also known by the alias “Pinocchio rex,” has been discovered in the exact same geological formation.
For the small Corythoraptor, this swift and ferocious carnivorous dinosaur would have undoubtedly been a terrifying natural enemy that constantly threatened its life.

Sporting a bizarre crest, Corythoraptor dashed across Late Cretaceous southern China alongside a diverse array of relatives.
Its wonderfully preserved fossils vividly convey to us the evolutionary path leading from dinosaurs to birds, as well as the rich ecosystem of that ancient era.

The Misconception of a “Super-Giant Carnivorous Dinosaur” and a 50-Year Blank

The arms of Deinocheirus are the second longest of any animal on Earth, surpassed only by Therizinosaurus.

A 30-Meter-Long Monster?

Considering that a Tyrannosaurus (13 meters or 42.6 feet long) has arms about 1 meter (3.3 feet) in length, a simple calculation suggested that Deinocheirus, with its 2.4-meter arms, would be a “super-giant carnivorous dinosaur” exceeding 30 meters (98 feet) in total length.
However, it was highly unrealistic for such a massive theropod to actually exist, leaving its true identity unknown for many years.

Expert Speculation and the Situation at the Time

Upon reinvestigating the original excavation site, researchers only found fragments of ribs bearing tooth marks, indicating they had been scavenged by a Tarbosaurus.
While Dr. Philip Currie from Canada and others supported the super-giant carnivore theory, Dr. Yoshitsugu Kobayashi from Japan and his colleagues speculated based on the arm structure that it was a member of the “ostrich dinosaurs” (ornithomimosaurs). However, lacking conclusive evidence, it remained a relatively obscure dinosaur.

The Discovery of the Century and the Dramatic Recovery from “Fossil Poachers”

After a long period of obscurity, the situation took a sudden turn between 2006 and 2009.
An international research team led by Dr. Yuong-Nam Lee of South Korea (which included Dr. Currie and Dr. Kobayashi) finally achieved the monumental feat of discovering “two nearly complete torso fossils.”

Poaching by Fossil Hunters

Tragically, the most highly prized parts—the skulls and the ends of the limbs—had already been hacked off by fossil poachers and smuggled into the black market.

Relentless Tracking and Return

Refusing to give up, the researchers tracked down the missing pieces and, in 2011, discovered they were in the possession of a European collector.
The fossils were repatriated to Mongolia in 2014, finally bringing the complete skeleton to light.

The “Bizarre True Form” Revealed

The reconstructed appearance unveiled in 2014 far exceeded anyone’s imagination.
Despite being an ostrich dinosaur, it exceeded 10 meters (32.8 feet) in length. Furthermore, recent studies indicate that its entire body was covered in feathers.

• A broad, flat, toothless “duck-like bill”
• A high, sail-like ridge of bones on its back (neural spines)
• Unusually long forelimbs and a massive, bulging “potbelly”

An Omnivorous “Fermentation Chamber” and the True Use of Its Terrible Hands

Although once thought to be a ferocious carnivorous dinosaur, fish bones, scales, and plant seeds and fibers were found in its stomach, confirming that Deinocheirus was actually an omnivore.

Swallowing Whole and Grinding with “Gastroliths”

Unable to chew, it used its bill to scoop up fish, aquatic plants, and leaves from low shrubs in shallow waters, swallowing them whole.
In its gastrointestinal tract—which functioned like a “fermentation chamber” inside its massive potbelly—it took its time digesting and absorbing nutrients using swallowed pebbles (gastroliths) to grind up the food.
It is speculated that this evolutionary trait served to lighten its head while maintaining a weight balance against its massive arms and tail.

The Role of the “Terrible Hands”

The movement of its arms was sluggish, making them unsuitable for hunting.
Today, it is believed they were used to pull down tree branches or to dig up riverbeds with their tough claws in search of aquatic life.
They also served as a “defensive weapon” to protect itself from large carnivorous dinosaurs like Tarbosaurus.

Eggs Arranged in a Donut Shape and Devoted Parenting

Regarding its reproductive habits, interesting behaviors have been inferred from the fossilized eggs of closely related species.

They laid their eggs arranged in a “donut shape” with an empty space in the middle.
This was an ingenious method to prevent the parents from accidentally crushing the eggs, while allowing the parent to sit in the central space and efficiently incubate the eggs using its feathers.

Summary

Nearly half a century has passed since it was named in 1970.
Overcoming the crisis of poaching, the “creepy, arms-only monster” underwent a dramatic transformation into a “giant, feathered, duck-billed omnivorous dinosaur” that leisurely dined by the water’s edge.

Its extraordinary fate was featured in major events like the 2019 Dinosaur Expo in Japan, and it is now an incredibly popular dinosaur worldwide.
It can be considered one of the most dramatic discoveries in the history of paleontology, perfectly demonstrating how a single fossil piece can completely overturn conventional wisdom.

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.