An Ultimate Guide to Coelophysis: The Hollow Form

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Name Meaning“Hollow form”Height4 meters (13 feet)
PronunciationSee-loh-fy-sissLength2 metres (6.6 feet)
EraMesozoicLate TriassicWeight15–25 kilograms (33–55 pounds)
ClassificationDinosauria, Saurischia & TheropodaLocationNew Mexico, United States 

Coelophysis Pictures

Coelophysis | Elenarts108 via iStock

The Coelophysis

Gage Beasley Prehistoric's Coelophysis Concept
Gage Beasley Prehistoric’s Coelophysis Concept

Also known as the hollow form, the Coelophysis was among the first discovered and named dinosaur genera.

Supposedly, the genus is known from more than 1,000 specimens, most of them unearthed from New Mexico’s Ghost Ranch.

They date from the Late Triassic, indicating that this small bipedal theropod walked on Earth roughly 228–201 million years ago.

Although many other fossils from around the world were associated with the genus, few of them are now recognized, and only one species is considered valid: Coelophysis bauri.

The Coelophysis was a carnivore but likely did not go for large prey, as its arms and teeth show evidence of killing small, lizard-like animals.

Its keen daytime eyesight probably proved it was a diurnal creature.

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

Considering how many specimens were found in the same locality, scientists rushed to argue that the Coelophysis engaged in gregarious behavior.

We encourage you to keep reading if you want to learn more about this primitive dinosaur!

We’ve prepared quite a comprehensive guide to the genus!

Physical Characteristics

The Coelophysis is among the few theropods known from several complete skeletons.

It was one of the lightest dinosaurs, weighing only 15–25 kilograms (33–55 pounds).

Considering its body mass, you’d expect a dinosaur as small as a dog, right?

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

In reality, it could reach lengths of three meters (9.8 feet)!

Other members of the same family (Coelophysidae) were just as small and light.

The Megapnosaurus, for example, measured 2.2 meters (7.2 feet) long and weighed only 13 kilograms (29 pounds).

The Procompsognathus was even tinier, reaching only a meter (3.3 feet) long and having a body mass of 1–1.3 kilograms (2.2–2.8 pounds).

The Segisaurus was just as short as the Procompsognathus but weighed 4–7 kilograms (8.8–15 pounds).

As such, we can even state that the Coelophysis was the largest among others of its kind!

Coelophysis 3D illustration
Coelophysis 3D illustration | Warpaintcobra via iStock

Other characteristics of the genus include the following:

  • It had a long, narrow head, measuring approximately 27 centimeters (10 inches).
  • The teeth were blade-like and recurved. They were finely serrated on the posterior and anterior edges.
  • The eyes were large and faced forward.
  • It had a stereoscopic vision that ensured good depth perception. Its vision was similar to that of modern birds of prey, with the eyes resembling eagle and hawk eyes. On the other hand, night vision was probably poorly developed.
  • The snout was elongated and featured large fenestrae, contributing to its lightweight.
  • The neck was relatively long and featured a sigmoid curve.
  • The forelimbs were short and bore four digits, of which only three were functional, whereas the fourth was embedded in the flesh. The hands were specialized in grasping prey.
  • The hips were narrow.
  • The hindlimbs were long and sturdy and bore three toes each and a raised dewclaw.
  • The tail was remarkably long and featured a distinctive structure, ensuring it didn’t move up and down.

Besides the above, Coelophysis fossils show evidence of a furcula, a forked bone known in most bird species but only in some non-avian dinosaurs.

Back then, this discovery was the first proof that at least some dinosaurs possessed a wishbone (furcula).

Habitat and Distribution

The earliest Coelophysis fossils were discovered in New Mexico’s Chinle Formation.

Some of the most notable specimens were unearthed at Ghost Ranch.

Another specimen recovered from the Portland Formation in Connecticut may have been a Coelophysis, but this hasn’t been fully confirmed yet.

South Africa’s Upper Elliot Formation and Zimbabwe’s Forest Sandstone Formation revealed other specimens that are now assigned to the Megapnosaurus, which has been historically thought to be a species of the Coelophysis genus.

The Megapnosaurus genus isn’t fully approved yet, but if it were indeed a type of Coelophysis, this would greatly extend the distribution of these primitive theropods.

During the Late Triassic, our world was experiencing a semiarid climate with seasonal heavy rains.

Coelophysis dinosaur walking in its own habitat
Coelophysis dinosaur walking in its own habitat | Roger Harris via GettyImages

Over 200 million years ago, when the Coelophysis was alive, Ghost Ranch was close to the equator, which ensured a warm climate with wet and dry seasons.

The environment likely featured floodplains.

The flora was quite diverse, although probably dominated by conifers that grew in various forms, from large trees to small shrubs.

Cycads, tree ferns, and palm-like trees were also abundant. 

Behavior and Diet

The Coelophysis was an obligate biped.

The form of its teeth indicates it was a carnivorous theropod, while the weak arms, specialized in grasping prey, show that it typically hunted smaller animals.

The bipedal Coelophysis
The bipedal Coelophysis | Vac1 via iStock

Some fossilized specimens revealed juveniles of the same species within their abdominal cavities, which prompted specialists to suspect that these theropods engaged in cannibalistic behavior.

Other scientists rushed to disapprove of this theory, suggesting that the skeletons found in the abdomen were, in fact, crurotarsan reptiles.

Another fascinating behavioral trait associated with Coelophysis is gregariousness.

The Ghost Ranch revealed more than a thousand specimens associated with Coelophysis.

This discovery indicates that these Late Triassic theropods may have walked and hunted in packs.

Coelophysis was a bipedal predatory dinosaur that lived during the Triassic Period of North America
Coelophysis was a bipedal predatory dinosaur that lived during the Triassic Period of North America | CoreyFord via iStock

However, it is not direct evidence of pack behavior, as it may simply indicate that these individuals were buried in the same place upon gathering to drink from a water source or feed.

As already mentioned, the Coelophysis had excellent daytime vision, suggesting it was diurnal.

The nighttime vision was poorly developed. 

Life Cycle

Coelophysis specimens may have been sexually dimorphic.

Upon studying the discovered specimens, scientists concluded that there were two “morphs.”

Coelophysis standing on a full moon
Coelophysis standing on a full moon | Daniel Eskridge via iStock

One was more robust and had a shorter skull and neck, longer arms, and unfused sacral neural spines.

Supposedly, this was the male.

The other (the female) was more gracile and had a longer skull and neck, fused sacral neural spines, and shorter arms.

These differences could be observed even in juveniles, suggesting that this sexual dimorphism (if it was indeed sexual dimorphism) developed even before the young reached sexual maturity.

Like all dinosaurs, the Coelophysis reproduced by laying eggs.

Paleongolotical data shows that its eggs were approximately 31-33.5 millimeters (1.2–1.3 inches) in diameter.

Females laid paired eggs. The clutches typically consisted of 24–26 eggs.

Many baby dinosaurs were precocial.

This means they could fend for themselves right after hatching.

Computer-generated 3D illustration with the dinosaur Coelophysis in a landscape
Computer-generated 3D illustration with the dinosaur Coelophysis in a landscape | MR1805 via iStock

Coelophysis offspring, however, required parental care until they reached the end of the first growth stage, meaning when they were one year old.

By that time, they were approximately 1.5 meters (4.9 feet) long.

Other studies show that, considering how rapidly they grew during their first year, only minimal parental care was required.

After the first stage, the growth slowed down a bit.

The second growth stage ended when they were two years old, the third when they were four years old, and the fourth when they were 7–8 years old.

When they were eight, Coelophysis juveniles were three meters (10 feet) long and had reached sexual maturity.

Evolution and History

A Ceolophysis hunts in a dense Jurassic era forest
A Ceolophysis hunts in a dense Jurassic era forest | Daniel Eskridge via iStock

The earliest theropods (Eodromaeus and Herrerasaurids) date from the Late Triassic.

However, these forms are poorly known.

As such, today, the earliest true theropods are the members of the Coelophysoidea group, which includes the Coelophysis.

Therefore, the Coelophysis holds a significant place in the evolutionary tree of theropods, probably being ancestral to all theropods.

The Coelophysis genus consists of only one recognized species, Coelophysis bauri.

The other two species, Coelophysis willistoni and Coelophysis longicollis, were confirmed to be dubious.

Illustration of Ceolophysis on ink
Illustration of Ceolophysis on ink | Pimpay via iStock

Coelophysis kayantekatae is a fourth possible species, but the fossils associated with it are now considered part of the Megapnosaurus genus.

Nevertheless, not all scientists recognize the Megapnosaurus genus.

As you can see, things aren’t as easy as they seem at first, right?

The paleontological history of the Coelophysis dates back to 1881, when David Baldwin, an amateur fossil collector, discovered some fossil dinosaurs in northwestern New Mexico.

Six years later, Edward Drinker Cope classified these specimens into two species under the Coelurus genus.

Only in 1889 did he create a separate genus, Coelophysis.

Over the years, this genus has been reassigned multiple times, only to be finally recognized as a member of the Coelophysoidea superfamily in the Neotheropoda clade.

Interactions with Other Species

Coelophysis isolated on white background
Coelophysis isolated on white background | Vac1 via iStock

The Chinle Formation of the Western United States is widely renowned for its archosaur fossils.

Paleontological expeditions revealed remains that belonged to over 30 types of animals, including phytosaurs, aetosaurs, crocodylomorphs, paracrocodylomorphs, avemetatarsalians, and various dinosaurs.

The Coelophysis, which was undoubtedly abundant, shared its habitat with other theropods, among them Camposaurus, Daemonosaurus, and Tawa.

The Chindesaurus, a saurischian dinosaur, may have been a cohabitant.

However, these dinosaurs weren’t nearly as common as other reptiles like the Whitakersaurus, Revueltosaurus, or Hesperosuchus

Photorealistic image of a Coelophysis
Photorealistic image of a Coelophysis | leonello via iStock

Amphibians were also quite common, as were cartilaginous fish, ray-finned fish, and lobe-finned fish, although the Coelophysis probably never crossed paths with them as it was a terrestrial creature.

Therefore, while the Coelophysis certainly lived in a diverse and rich habitat in terms of wildlife, we do not know to what extent it interacted with other species.

Scientists suspect there may have been some competition for food and water during the drier season.

Further than that, its daily routines remain a mystery.

Cultural Significance

Besides serving as inspiration for envisioning the environment of Late Triassic North America, the Coelophysis holds an essential role in the evolutionary history of theropods.

Considering how many specimens were recovered from the United States, it’s unsurprising that the appearance, lifestyle, diet, and reproduction of this theropod were the subjects of multiple studies aimed at shedding light on unknown aspects of the theropod lineage.

Coelophysis lurking to find prey
Coelophysis lurking to find prey | Vac1 via iStock

The Coelophysis is also a popular appearance in the media, appearing as a character in the following productions:

  • Walking with Dinosaurs
  • When Dinosaurs Roamed America
  • Mammals Vs Dinos
  • Bizzare Dinosaurs
  • Zoo Tycoon: Dinosaur Digs
  • Dinosaur Explorers video game
  • Dinosaurs: Fun, Fact, and Fantasy


The Coelophysis is often regarded as one of the most primitive theropod forms.

It was a bipedal carnivore that roamed the territory we now call the southwestern United States.

It was alive 229–201 million years ago, during the Late Triassic.

The hollow form was a small theropod and likely a fast runner that relied primarily on its keen eyesight during hunting.

Although it measured approximately three meters (9.8 feet) long, it was remarkably light, probably not reaching more than 20 kilograms (44 pounds).

Its arms were relatively weak and adapted for grasping prey.

This indicates that the Coelophysis preyed on small, lizard-like animals.

Paleontological discoveries also showed that it may have hunted in large packs.


Did Coelophysis live with the Velociraptor?

The Coelophysis did not live with the Velociraptor, as the latter was a Late Cretaceous theropod and roamed our planet 75–71 million years ago.

Was Coelophysis a raptor?

The term raptor is used in regard to the members of the Dromaeosauridae family within the Theropoda clade.

While the Coelophysis was a theropod, it was not a member of this family, thus not a raptor.


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