An Ultimate Guide to Deinocheirus: The Terrible Hand

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Name MeaningTerrible HandHeight4–5 meters (13–16 feet)
PronunciationDie-noe-ky-rusLength10–12 meters (33–39 feet)
EraMesozoicLate CretaceousWeight7.2 metric tons (15,800 lbs)
ClassificationDinosauria,‭ Saurischia & SauropodaLocationMongolia

Deinocheirus Pictures

Deinocheirus was an ostrich dinosaur that lived in the Late Cretaceous Era of Mongolia
Deinocheirus was an ostrich dinosaur that lived in the Late Cretaceous Era of Mongolia | CoreyFord via iStock

The Deinocheirus

Gage Beasley Prehistoric's Deinocheirus Concept
Gage Beasley Prehistoric’s Deinocheirus Concept

Deinocheirus was a genus of ornithomimosaur that lived during the Late Cretaceous.

For several decades after its initial discovery, Deinocheirus was one of the world’s most mysterious dinosaurs.

The first fossils of this massive dinosaur were discovered in the Nemegt Formation of Mongolia in 1965. 

It consisted of a pair of long arm bones with big, long claws. 

Each of these claws was over seven inches (20 centimeters) long. 

Scientists were so bewildered by these bizarre-looking claws the dinosaur immediately got the name Deinocheirus which translates as “terrible claws.” 

Image of Deinocheirus claw
Image of Deinocheirus claw | Kabacchi via Wikimedia Commons CCA 2.0

Based on the size of the claws, scientists were certain they had a massive beast on their hands, but without a full skeleton, estimating the actual size of this dinosaur was impossible. 

What followed was an over half-century search for the 70 million years old giant. 

Paleontologists made several expeditions to Mongolia to find the rest of the animals without success. 

This made it difficult to reconstruct this dinosaur’s appearance and properly place it in the right lineage on the dinosaur family tree. 

Scientists could only imagine the true identity of the enormous long-armed dinosaur. 

The discovery of a complete specimen of this dinosaur made it possible to start piecing together its possible appearance. 

What they found was an enormous hump-backed dinosaur that exceeded anything scientists could have imagined. 

In this post, we’ll explain some of the most fascinating details about this dinosaur, including its bizarre appearance and where and how it lived. 

Gage Beasley's Prehistoric Shirt Collection
Gage Beasley’s Prehistoric Shirt Collection
Gage Beasley's Prehistoric Plush Collection
Gage Beasley’s Prehistoric Plush Collection

Physical Characteristics

Deinocheirus was a massive dinosaur. 

It is the largest member of this group of ostrich-like dinosaurs and one of the largest theropod dinosaurs ever found, rivaling the famous Tyrannosaurus rex in size. 

The estimated length for the Deinocheirus is about 10 to 12 meters (33 to 39 feet). 

It was also quite tall, standing around four to five meters (13 to 16 feet) at the hips. 

Gage Beasley Prehistoric's Deinocheirus Size Comparison Chart
Gage Beasley Prehistoric’s Deinocheirus Size Comparison Chart

For context, the Tyrannosaurus rex measured about 40 feet in length, which means both dinosaurs were roughly the same size. 

Deinocheirus had a bulky, pot-bellied appearance, a humped back, and a long slender neck. 

It had a low, narrow skull with an elongated snout. 

The widest part of the skull measured about 9.1 inches (23 centimeters), and the skull was about 1.024 meters (3.36 feet) on average. 

The most striking feature of Deinocheirus was its arms.

The arms were exceptionally long, reaching lengths of around 2.5 meters (8.2 feet). 

The Deinocheirus had one of the longest forelimbs of all the bipedal dinosaurs.

Deinocheirus dinosaur walking while roaring
Deinocheirus dinosaur walking while roaring |Elenarts108 via iStock

These arms were slender, with three-fingered hands. 

Each finger had large blunt claws, probably useful for grasping and manipulating objects.

Despite its massive size, Deinocheirus was not very heavy.  

The dinosaur’s bones were thin, suggesting a low average weight compared to dinosaurs of the same size.

The maximum estimated weight for this dinosaur is about 7.2 tons, but it may have been lower too. 

Deinocheirus also had a large fan-shaped hump on its back formed by neural spines that grew increasingly longer from the front to the back. 

Skeletal diagram of deinocheirus dinosaur
Skeletal diagram of deinocheirus dinosaur | Michael B.H. via Wikimedia Commons CC BY-SA 3.0

Although no soft tissues have been found for this dinosaur, ornithomimosaurs, in general, are known to have possessed pennaceous feathers all over their body.

The Deinocheirus probably had this hair covering, too and may have a fan of feathers as its tail. 

Habitat and Distribution

Deinocheirus lived in parts of present-day Mongolia during the Late Cretaceous Period. 

Fossils of this dinosaur have been recovered from the Nemegt formation, located in the Gobi Desert region of Mongolia. 

This suggests that the dinosaur’s range was probably restricted to this part of the country, specifically in the Nemegt Basin located in the southwestern region of Mongolia. 

Seventy million years ago, the Gobi Desert where this dinosaur lived was not the arid wasteland it is today. 

Instead, it consisted of vast floodplains with a large river system that gave rise to wetland ecosystems. 

Some parts of this region also had some degree of forest cover, populated by conifer trees, ferns, and flowering plants. 

This dinosaur species walking among ponds calamites trees by day
This dinosaur species walking among ponds calamites trees by day | Elenarts108 via iStock

Deinocheirus is believed to have lived in the vast floodplains in this region close to water sources where it could find abundant plant materials that formed the bulk of its diet. 

The environment in the Nemegt Basin was generally warm and humid during this period.

The region experienced seasonal rainfall, which contributed to the development of river systems and created suitable habitats for dinosaurs and non-dinosaur species. 

Behavior and Diet

Ornithomimosaurs are known for being fast and agile dinosaurs. 

The Deinocheirus was an exception to this rule. 

Given its size and skeletal structure, Deinocheirus was most likely a slow-moving dinosaur. 

The social behavior of Deinocheirus is uncertain, but they may have lived in small groups. 

Deinocheirus had a broad bill, a humpback-like sail, and tall neural spines
Deinocheirus had a broad bill, a humpback-like sail, and tall neural spines | Johnson Mortimer via Wikimedia Commons CCA 3.0

This dinosaur’s long neural spines and tail fan probably served display purposes, which is consistent for animals that lived in herds. 

Scientists have reconstructed the likely brain structure of the Deinocheirus using CT scans. 

The studies show that this dinosaur had large olfactory tracts, but the sclerotic rings of their eyes were relatively small compared to the length of the skull. 

This suggests the Deinocheirus was most likely diurnal (active during the day).

When the first fossils of the Deinocheirus were discovered, the massive arms with long curved claws invoked the image of a beastly carnivore similar to the allosaurs or dromaeosaurid dinosaurs. 

The discovery of more complete specimens has helped to clarify the initial confusion about the dinosaur’s diet. 

Like other ornithomimosaurs, the Deinocheirus was probably a herbivore or omnivore. 

Deinocheirus dinosaur fishing by day
Deinocheirus dinosaur fishing by day | Elenarts108 via iStock

It ate plant materials, but the presence of fish vertebrae and scales in the gut content of this dinosaur suggests that it probably preyed on fish and small reptiles as well. 

Deinocheirus had gastroliths in its stomach for grinding up its food. 

In one specimen of this dinosaur, scientists found at least 1,000 gastroliths in its gut, 

The duck-like beak of this dinosaur suggests that it probably foraged near water or browsed on low-lying plants like some sauropods and hadrosaurs do. 

This dinosaur’s beak had a weak bite force, indicating that they were adapted for cropping soft plants that grew in the understory or close to the water. 

It probably had a flexible tongue that was useful for sucking the plant materials into its broad beak. 

To obtain the small animals that were a part of its diet, the Deinocheirus probably used its long beaks to probe shallow water for fish, insects, and other small creatures. 

Life Cycle

This dinosaur species was one of the largest ornithomimosaurs
This dinosaur species was one of the largest ornithomimosaurs | Sergey Krasovskiy via GettyImages

Deinocheirus, like other dinosaurs, reproduced sexually. 

Since they had structures that were likely useful for display, such as the prominent hump, body, and tail features, this dinosaur probably engaged in some sort of courtship behavior to attract a mate. 

After mating, females would have laid eggs in nests built on the ground. 

So far, no nests associated with the Deinocheirus or other ornithomimosaur dinosaurs have been found.

But it would not be far-fetched to assume that they made nests similar to modern birds. 

It isn’t clear if this dinosaur exhibited any form of parental care for its young. 

After hatching from eggs, juveniles either lived in juvenile groups along with other young Deinocheirus or joined the same herds as the adults. 

3D illustration of Deinocheirus dinosaur walking isolated in white background
3D illustration of Deinocheirus dinosaur walking isolated in white background | Elenarts108 via iStock

Like other theropod dinosaurs, the growth rate of the Deinocheirus was probably very fast. 

They grew from small, vulnerable juveniles to fully grown adults within a relatively short time, attaining maturity within the first few years. 

Their growth would eventually slow down after attaining adulthood. 

Evolution and History

Deinocheirus belongs to the Ornithomimosauria dinosaur group, also known as the bird-mimic dinosaurs. 

This is a group of theropod dinosaurs known for their bird-like characteristics. 

The earliest members of this group evolved during the Early Cretaceous Period. 

The Deinocheirus is considered one of the basal members of this group. 

The arms of this dinosaur species were among the largest of any bipedal dinosaur with large, blunt claws on its three-fingered hands
The arms of this dinosaur species were among the largest of any bipedal dinosaur with large, blunt claws on its three-fingered hands | UnexpectedDinoLesson via Wikimedia Commons CC A-SA 4.0

One of the major adaptations developed by this dinosaur was its elongated forearms, which are unlike that of most of the other theropod dinosaurs. 

The Deinocheirus’ forelimbs may have been the longest of all the bipedal dinosaurs.

The long arms and claws of this dinosaur were useful for digging and gathering plants.

This unique adaptation would have significantly influenced this dinosaur’s feeding behavior. 

Deinocheirus evolved to be bigger than any of the other ornithomimosaurs. 

A consequence of this adaptation is that this dinosaur was probably not as agile as its relatives.

However, the dinosaur’s bones were pneumatized, which would have helped to keep its weight low compared to other similar-sized dinosaurs. 

Interactions With Other Species

A mother Deinocheirus dinosaur and two dinosaur species watch as Argentinosaurus make their way through swallow lake waters
A mother Deinocheirus dinosaur and two dinosaur species watch as Argentinosaurus make their way through swallow lake waters | CoreyFord via iStock

Deinocheirus lived in the Nemegt Basin, which was a fertile plain during the Late Cretaceous Period. 

This region probably supported a thriving ecosystem that included different species of plants and animals. 

Deinocheirus fed on tree plants, including ferns, conifers, and flowering plants in its ecosystem. 

Its diet may have also included fish, reptiles, and other small animals, but the bulk of this dinosaur’s nutrition most likely came from plants. 

It did have to contend for these plant materials with other large herbivores in its ecosystem, such as the Therizinosaurus

The Late Cretaceous ecosystem also included various titanosaurian sauropods and smaller hadrosaurids.

Argentinosaurus dinosaurs are part of titanosaurian sauropods and considered one of the largest dinosaurs ever discovered
Argentinosaurus dinosaurs are part of titanosaurian sauropods and considered one of the largest dinosaurs ever discovered | Elenarts108 via iStock

These herbivores would have competed with the Deinocheirus for foliage and other resources.

The Deinocheirus’ ability to feed on other food sources apart from plants would have given it an edge over the competitors in its ecosystem. 

The Deinocheirus lived alongside several predatory theropods. 

The biggest of them was the Tarbosaurus which was large enough to be considered a likely prey of this dinosaur. 

Other predator species that lived close by include Alioramus, Bagaraatan, and troodontids like the Borogovia and Tochisaurus

Given the massive size of the Deinocheirus, many of these predators didn’t pose a significant threat to adult dinosaurs. 

But the juveniles and weak individuals were probably easy pickings for prey. 

Despite its large size, Deinocheirus did not have teeth. Instead, it had a toothless beak.
Despite its large size, Deinocheirus did not have teeth. Instead, it had a toothless beak | CoreyFord via iStock

The fact that this dinosaur was slow and lacked any major defensive mechanisms would have made them vulnerable to large theropod predators. 

Cultural Significance

For more than 50 years after its initial discovery, the Deinocheirus was nothing more than a gigantic pair of arms.

Scientists were certain of this dinosaur’s existence, but the available fossils provided very limited knowledge about what it looked like. 

The quest to find the complete remains of this dinosaur sparked a frenzy of expeditions in the region where the previous fossil was discovered. 

Failure to find additional fossils turned Deinocheirus into one of paleontology’s mysteries. 

This mystery was eventually solved in 2014 when scientists found two additional remains of this dinosaur in relatively good condition. 

Reconstructed skeleton of deinocheirus in Japan
Reconstructed skeleton of deinocheirus in Japan | image via Wikimedia Commons CC A-SA 4.0

The discovery of these fossils finally made it possible to put a face to the name and uncover many of the unknown details of this dinosaur’s life. 

Still, many aspects of this dinosaur’s life remain unknown and are still actively studied. 

Fossils of the Deinocheirus are known from the Nemegt Formation, one of the most productive dinosaur graveyards in the world. 

The discovery of this dinosaur has played an important role in our interpretation of this prehistoric ecosystem and its condition several million years ago. 

Deinocheirus is arguably one of the most important fossils known from that region, and the quest to find this dinosaur led to the discovery of many more fossils in the area. 

The dinosaur has been known to the general public for years, even before the mystery of the gigantic arms was solved. It is frequently mentioned in books, documentaries, and museum exhibitions. 

And now that more fossils of this dinosaur have turned up, there’ll be even more interesting discoveries as scientists continue to study its bones to better understand how it lived. 


Deinocheirus was a large ornithomimosaurid that lived towards the end of the Cretaceous Period. 

It was one of the most enigmatic dinosaurs in history. 

For several decades after this dinosaur’s initial discovery, all scientists had was a pair of large arms, shoulder girdles, and a few other bones. 

The size of the arm was impressive enough to raise curiosity about the dinosaur’s identity.  

More than five decades later, the discovery of additional fossils eventually laid the mystery of the Deinocheirus to rest. 

Despite the dinosaur’s intimidating name, the Deinocheirus’ massive claws were not a weapon for killing prey. 

The dinosaur was an omnivore, and the large claws were useful for digging and gathering plants.

Although the mystery of the “terrible hand” has been laid to rest, there’s still a lot to know about this dinosaur and the life it lived before it went extinct 70 million years ago. 


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