An Ultimate Guide to Ornithomimus: The Bird Imitator

Leave a comment / / Updated on: 24th September 2023

Name Meaning“Bird mimic”Height1-1.2 meters (3-3.9 feet)
PronunciationOr-knee-thow-my-musLength3-3.8 meters (9.8-12.5 feet)
EraMesozoicLate CretaceousWeight170 kilograms (375 pounds)
ClassificationDinosauria, Saurischia & TheropodaLocationWestern North America 

Ornithomimus Pictures

Ornithomimus | Mark Garlick via GettyImages

The Ornithomimus

Gage Beasley Prehistoric's Ornithomimus Concept
Gage Beasley Prehistoric’s Ornithomimus Concept

The Ornithomimus was an American dinosaur.

While fossils from other parts of the world were assigned to this genus, scientists haven’t fully confirmed their taxonomic classification.

As such, the most important Ornithomimus fossils are now thought to have been unearthed in Alberta, Canada, and Colorado, United States.

These fossils date from the Late Cretaceous and belong to a small bipedal theropod measuring up to 3.8 meters (12.5 feet) long.

It had a bird-like beak, a long neck, a short torso, and long limbs, which prompted many wildlife enthusiasts to call it one of the world’s fastest dinosaurs!

If you’re eager to learn more about the Ornithomimus, keep reading, as we’ve gathered a myriad of curiosities about it!

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

Physical Characteristics

Ornithomimus artist sketch
Ornithomimus artist sketch | Sebastian Kaulitzki via GettyImages

The Ornithomimus was a bipedal ornithomimid theropod.

Its build was similar to the modern ratites in the Palaeognathae infraclass.

It had long, slender hindlimbs, a long neck, and a short yet wide torso.

The forelimbs were unusually long and robust for a bipedal dinosaur and ended in powerful claws.

While it has been historically thought that the Ornithomimus was covered in scales, recent discoveries carry proof of a feathered body.

Paleontological expeditions revealed evidence of pennaceous feather shafts on some specimens.

Moreover, specialists found hair-like filaments on a juvenile’s rump, neck, and legs.

Upon studying feather growth in Ornithomimus, researchers concluded that these dinosaurs were covered in filamentous feathers regardless of age and that only adults developed wing-like structures.

In 2015, paleontologists unearthed another feathered Ornithomimus individual.

Feathered Ornithomimus
Feathered Ornithomimus | Sebastian Kaulitzki via GettyImages

This specimen carried evidence of a feathered tail.

The feathers were unusually similar to ostrich feathers, indicating that the Ornithomimus may have had similar plumage.

Additionally, this specimen revealed that the theropod likely had a bare skin patch from mid-thigh to the feet.

A skin contour probably connected the upper thigh and the torso.

This made it similar to modern birds, except that this structure is known as a skin web in modern species.

This discovery brings to light essential knowledge about the evolution of birds, as it made the Ornithomimus the first known dinosaur to have had such soft tissue structures.

Before discussing the size of the Ornithomimus, we must mention that the genus consists of two recognized species: Ornithomimus velox and Ornithomimus edmontonicus.

This information is of the essence in regard to length and weight because it is thought that the two differed in size.

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

O. edmontonicus was likely larger than O. velox, measuring approximately 3.8 meters (12.5 feet) long and weighing 170 kilograms (375 pounds).

The exact size of O. velox hasn’t been confirmed, but it is thought to be no longer than three meters (9.8 feet).

These estimations were done based on two second metacarpals, one for each species.

As for its height, the Ornithomimus likely didn’t grow taller than 1–1.2 meters (3.3–3.9 feet) at the hips.

This makes it smaller than other members of the Ornithomimidae family.

The Gallimimus, for example, was much taller, reaching 1.9 meters (6.2 feet) at the hips.

It was also twice as long as the Ornithomimus, measuring 6 meters (19.7 feet) long.

Habitat and Distribution

The exact distribution of the Ornithomimus remains unknown, and you’ll soon understand why.

While it is widely accepted that the Ornithomimus lived in Western North America, the mystery surrounding the fossils assigned to the genus makes it impossible to guess how widely distributed it was.

Over the years, numerous fossils have been wrongly attributed to the genus.

Some were even unearthed in China!

Scientists named more than 10 species based on these fossils, which were later reassigned to other genera.

Therefore, the species became invalid.

Here are some locations that served as homes to Ornithomimus fossils for millions of years:

  • Denver Formation, Colorado
  • Horseshoe Canyon Formation, Alberta
  • Dinosaur Park Formation, Alberta
  • Ferris Formation, Wyoming
  • Possibly Lance Formation, Wyoming

Although some fossils found in these localities are officially recognized as belonging to Ornithomimus, others are not so much.

Two Ornithomimus living in their habitat in the ancient past
Two Ornithomimus living in their habitat in the ancient past | Savany via iStock

For example, some specimens unearthed from the Dinosaur Park Formation are attributed to Ornithomimus samueli, but this isn’t a fully recognized species.

The locations that revealed the best Ornithomimus fossils are Alberta’s Horseshoe Canyon Formation and Colorado’s Denver Formation.

The Horseshoe Canyon Formation was likely a highly aquatic habitat featuring coal swamps, floodplains, and estuarine channels.

It probably had a relatively warm and humid climate.

When the Ornithomimus was alive, the formation underwent some paleoclimatic shifts linked to soil drainage conditions.

They caused a slight drop in temperature and precipitation and favored an unstable landscape.

The Denver Formation is thought to have had a cold, semi-arid climate.

It consists of fluvial, alluvial, and paludal deposits at the foot of the Rocky Mountain Front Ranges.

Ornithomimus dinosaurs swallowing stones along a stream as part of their diet, known as geophagy
Ornithomimus dinosaurs swallowing stones along a stream as part of their diet, known as geophagy | Sergey Krasovskiy via GettyImages

The territory includes the aquifers that were important sources of water.

Volcanic eruptions may have marked the environment.

However, they most likely occurred during the Paleocene, by the time the Ornithomimus was already extinct.

The highly changing environment of prehistoric Western North America can also be linked to sea level changes and soil drainage conditions.

Looking back at these two formations, we can conclude that the Ornithomimus adapted to various habitats, from warm and humid wetlands to dry and cool forested areas.

Behavior and Diet

Ornithomimus lurking around
Ornithomimus lurking around | Savany via iStock

As already mentioned, the Ornithomimus was a bipedal dinosaur.

The long yet robust hind limbs made it an excellent runner.

Some sources mention that it could move at speeds of up to 65 km/h (40.4 mph).

Things aren’t as clear regarding its diet, as scientists aren’t sure whether it was a carnivore or an herbivore.

Many theropods were carnivores, but the body build of the Ornithomimus suggests a rather herbivorous lifestyle.

Its elongated, bird-like beak supports this theory.

Some argue that the Ornithomimus was an omnivorous theropod, feeding on crustaceans, fruits, branches, leaves, insects, lizards, and even small mammals.

It has even been suggested that ornithomimids, including the Ornithomimus, depended on waterborne food sources and relied primarily on filter feeding.

Colorful Ornithomimus Velox
Colorful Ornithomimus Velox | james63 via iStock

Nevertheless, future findings are a must to understand its diet to the fullest.

Whether the Ornithomimus relied on its speed to catch prey (if any) remains unknown, but it was undoubtedly of tremendous help to escape predators!

Another thing worth mentioning about the lifestyle of Ornithomimus dinosaurs is that they were probably nocturnal.

Fossilized specimens revealed large eye sockets, indicators of keen eyesight possibly adapted to a nocturnal lifestyle.

Their brains were also unusually large, most likely associated with kinesthetic coordination rather than high intelligence.

Members of the Ornithomimosauria clade, which the Ornithomimus is part of, are thought to have been highly gregarious, although this hasn’t been fully confirmed for it.

Life Cycle

A walking feathered Ornithomimus
A walking feathered Ornithomimus | Sebastian Kaulitzki via GettyImages

Like all dinosaurs, theropods, including the Ornithomimus, reproduced by laying eggs.

Females had paired ovaries and oviducts, while males had internal testes and a retractable penis.

Female theropods also possessed a crocodilian-like internal system where mature eggs were stored before fertilization.

Once fertilization occurred, they laid pairs of eggs.

It remains unknown which theropods incubated their eggs, but scientists assume that at least some species relied on incubation.

If the Ornithomimus were one of them, it incubated the eggs for approximately 60–90 days.

Ornithomimus mother dinosaur with juveniles, along with an adult male in a Cretaceous forest
Ornithomimus mother dinosaur with juveniles, along with an adult male in a Cretaceous forest | Vitor Silva via GettyImages

The nesting behavior of the Ornithomimus remains a mystery as well.

What kind of nests did it build, how large were they, and where were they located? Were the eggs buried after being laid?

Probably the most well-known and complete theropod nest belonged to Troodon.

It consisted of 24 eggs laid in a shallow bowl-shaped depression featuring a rim.

Supposedly, the female built the nest and left it open after laying the eggs.

It would be impossible to confirm whether all theropods engaged in this reproductive behavior, but it’s still a start.

Evolution and History

Ornithomimus as shown in Jurassic World Alive
Ornithomimus as shown in Jurassic World Alive | Image via JWAFandom

The earliest theropods date from the Late Triassic.

During the Early Jurassic, the ecology allowed the development of relatively more advanced ceratosaurs.

By the Late Jurassic, there were already four distinct theropod lineages: ceratosaurs, allosaurs, megalosaurs, and coelurosaurs.

The Ornithomimus is part of the coelurosaur lineage, which is also the most diverse in the Theropoda group.

Other creatures like the Tyrannosaurus rex, Deinonychus, and Velociraptor are part of the same lineage.

During the Early Cretaceous, coelurosaurs became abundant.

George Lyman Cannot discovered the first Ornithomimus fossils in 1889, which were used to name the type species, Ornithomimus velox.

This dinosaur was initially thought to have been an ornithopod, but later ornithomimid fossils confirmed its classification in the Theropoda clade.

Ornithomimus skeleton illustration
Ornithomimus skeleton illustration | Peter Bull via GettyImages

In 1993, scientists named a second species, Ornithomimus edmontonicus, based on an almost complete skeleton discovered in Alberta’s Horseshoe Canyon Formation.

Another species, Ornithomimus samueli, is now placed in the genus but not fully confirmed.

It has been described based on a specimen recovered in 1901 from Alberta.

It was first named Struthiomimus samueli, then renamed Ornithomimus samueli.

Over the years, Ornithomimus samueli has repeatedly been renamed Dromiceiomimus samueli.

This classification hasn’t been confirmed by specialists yet.

More than 10 other species were named based on various fossils, but most of them were subsequently reassigned to other genera or considered nomen dubium, meaning doubtful species.

Interactions with Other Species

Ornithomimus finding its way to hunt
Ornithomimus finding its way to hunt | Sebastian Kaulitzki via GettyImages

Considering that most of the information known about the Ornithomimus has been derived from the fossils discovered in the Canadian Horseshoe Canyon Formation and Colorado’s Denver Formation, we’ll focus on the fauna of these two locations.

Naturally, we cannot confirm whether the Ornithomimus did indeed cross paths with any of these creatures.

However, since scientists confirm that these theropods were quite abundant during the Late Cretaceous, we cannot rule out the possibility that some interaction between species occurred.

It is believed that, at the time, ceratopsians and ornithomimids made up a third of the local fauna!

As such, here’s a comprehensive list of other prehistoric creatures that may have shared their habitat with the Ornithomimus:

Ankylosaurus | Emily Willoughby via Wikipedia CC BY-SA 3.0

Ankylosaurus like Anodontosaurus, Edmontonia, and Euoplocephalus

  • Maniraptorans like Albertavenator, Apatoraptor, and Atrociraptor
  • Mammals like Didelphodon
  • Alligatorids
  • Turtles

In the Horseshoe Canyon Formation, the Albertosaurus was likely the apex predator, so it may have preyed on the smaller Ornithomimus.

However, the Albertosaurus was probably much slower than our omnivorous theropod, and the latter may have easily escaped the ferocious predator!

Since the territory was abundant with herbivores, competition for food may have been a problem.

On the other hand, if the Ornithomimus were an omnivore, its diet would be much more varied than that of herbivores, so it likely would not suffer from a lack of food.

Cultural Significance

Life restoration of Ornithomimus
Life restoration of Ornithomimus | Tom Parker via Wikipedia CC BY-SA 4.0

The Ornithomimus is probably among the most widely studied dinosaur genera in terms of scientific classification and fossil identification.

More than 10 species assigned to this genus were later confirmed to have been wrongly placed under the Ornithomimus.

Can you imagine how much work this implied, how many scientists were involved, and how extensive the research has been?

Additionally, its remarkable resemblance to modern ostriches aroused the curiosity of renowned scientists!

Despite lacking the cultural popularity of other theropods, the Ornithomimus still served as inspiration for various characters in movies and video games.

It can be spotted in Fantasia, The Valley of Gwangi, The Land Before Time, and T. rex: Back to the Cretaceous.

In Dinosaur Train, it is wrongly depicted as being featherless and featuring quills on its head.

Cartoon ornithomimus on white background
Cartoon ornithomimus on white background | Tigatelu via iStock

The Ornithomimus creature in Jurassic Park III: Park Builder is also featherless.

Although it is sometimes wrongly depicted, its presence in the media brings the genus to people’s attention, thus enhancing its value in our world’s evolutionary history.


The Ornithomimus was a bipedal theropod living in Western North America roughly 76.5–66 million years ago.

It was likely an agile creature (often considered one of the fastest dinosaurs) that could easily escape predators.

It lived in quite a diverse ecosystem and was probably an omnivore, feeding on various plants, crustaceans, lizards, and small mammals.

The Ornithomimus had a relatively long neck, a short but wide torso, sloth-like forelimbs bearing claws, and long hind limbs, which ensured its agility.

It had keen eyesight and was probably nocturnal.

Hopefully, future findings will shed light on other aspects of this creature’s lifestyle!


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