An Ultimate Guide to Dryosaurus: The Tree Lizard

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

Name Meaning“Tree lizard”HeightLess than 1 meter (3.3 feet)
PronunciationDry-oh-sore-usLength3 meters (9.8 feet)
EraMesozoicLate JurassicWeight100 kilograms (220 pounds)
ClassificationDinosauria, Ornithischia, OrnithopodaLocationColorado (USA)

Dryosaurus Pictures

Dryosaurus | Sergey Krasovskiy via GettyImages

The Dryosaurus

Gage Beasley Prehistoric's Dryosaurus Concept
Gage Beasley Prehistoric’s Dryosaurus Concept

The Dryosaurus is also known as the tree lizard. 

Although this common name is widely believed to come from the distinctive form of its cheek teeth, Othniel Charles Marsh, the paleontologist who named the genus, probably referred to its habitat rather than its cheek teeth shape.

At only 3 meters (9.8 feet) long, the Dryosaurus was a bipedal herbivore with sturdy legs, making him an agile runner. 

It had a long neck and a long, stiff tail, the latter acting as a counterbalance. 

Its most distinctive characteristics are the horny beak and the cheek teeth.

The Dryosaurus genus consists of two species: Dryosaurus altus (the type species) and Dryosaurus elderae

Fossils attributed to the genus were discovered in the western United States. 

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

Some remains from Portugal may also belong to the Dryosaurus, but scientists haven’t yet confirmed this.

Although paleontologists unearthed an impressive number of individuals, all were juveniles, thus leaving many questions unanswered.

But do not falter; we’re always eager to learn something interesting about each dinosaur! And what we discover, we share with you!

Physical Characteristics

Cast of the D. elderae holotype skull
Cast of the D. elderae holotype skull | Jens Lallensack via Wikipedia CC BY-SA 4.0

The Dryosaurus had a long neck and tail.

It was a bipedal creature with short forelimbs and long, slender hindlimbs.

Each arm had five short fingers.

Like many other herbivores, the Dryosaurus’s beak-like structure helped crop plant matter. 

Additionally, it also had teeth in the back of its mouth.

Size estimations for the Dryosaurus can be highly inaccurate as no adult remains have been recovered. 

If we were to judge based on current estimations, we’d say the Dryosaurus was quite a small creature compared to other dinosaurs.

Gage Beasley Prehistoric's Dryosaurus Concept
Gage Beasley Prehistoric’s Dryosaurus Concept

The Dryosaurus reached lengths of only 3 meters (9.8 feet). 

It probably didn’t weigh more than 100 kilograms (220 pounds). 

However, as mentioned, this is likely not the maximum size.

Let’s compare it to other members of the same family to understand how large they were.

The Dysalotosaurus was approximately 2.5 meters (8.2 feet) long and weighed 80 kilograms (176 pounds).

The Valdosaurus wasn’t longer than 4-5 meters (13-16.4 feet) long.

The Callovosaurus, another member of the Dryosauridae family, was also quite small, measuring only 2.5 meters (8.2 feet) long.

Based on these numbers, we can conclude that, although the maximum size isn’t fully confirmed, the Dryosaurus was still a small dinosaur that probably didn’t exceed 4-5 meters (13-16.4 feet) long when fully mature.

However, some studies show that its characteristics indicate growth rates comparable to those observed in larger ornithopods, which means it may have grown larger than its close relatives. 

Either way, this question remains unanswered.

Habitat and Distribution

Here’s where Dryosaurus fossils were found:

  • Albany County, Wyoming
  • Upper Brushy Basin Member, Morrison Formation (partial skeleton, lower jaws, and a relatively complete skull)
  • Bone Cabin Quarry, Laramie, Wyoming
  • Dinosaur National Monument, Utah
  • Lily Park, Moffat County, Colorado
  • Uravan, Montrose County, Colorado
  • Possibly Portugal’s Lourinha Formation

Based on these details, we may assume that Dryosaurus was quite common on the North American continent. 

It may have even spread to Portugal!

It is thought that the Morrison Formation had a semiarid to tropical wet-dry climate viable for the growth of conifers, ginkgos, tree ferns, cycads, and horsetail rushes. 

The habitat likely featured river flood plains. It is believed the territory had wet and dry seasons.

The distictive banding of the Morrison Formation
The distinctive banding of the Morrison Formation | Michael Overton via Wikipedia  Michael Overton

Many of the dinosaurs discovered in the Morrison Formation were also found in Portugal’s Lourinha Formation, which is why we cannot rule out the possibility that the Dryosaurus also inhabited prehistoric Europe.

The Lourinha Formation is similar to the Morrison Formation in habitat, except it was wetter than the American territory. 

This is due to the position of both formations regarding the ocean.

While only some parts of the Morrison Formation were close to the water, the Portuguese Formation was altogether close to the recently opened North Atlantic, significantly shaping the ecosystem.

A study shows that the Lourinha Formation likely registered temperatures between 32 and 39 degrees Celsius (Fahrenheit), the average being 36 degrees Celsius (Fahrenheit).

Since the paleoenvironment was similar to the American Formation, we may assume that the Morrison Formation had the same temperatures, give or take some degrees.

Behavior and Diet

Dryosaurus walking as a bipedal ornithopod
Dryosaurus walking as a bipedal ornithopod | Nobumichi Tamura via GettyImages

The Dryosaurus was a bipedal ornithopod. 

It likely fed on low-growing riparian vegetation and used its efficient beak to crop the plants. 

Thanks to its sturdy legs, the Dryosaurus was a quick and agile runner, thus efficient at escaping predators. 

The long, stiff tail served as a counterbalance, further improving its odds against carnivores.

Unfortunately, very little is known about this creature’s behavior and lifestyle besides this. 

Was it social? If yes, to what degree? When was it active? What plants precisely did it feed on, and how much food did it require to survive? How often did it forage?

All these are valid questions awaiting future findings that could provide clear answers.

Life Cycle

The Dryosaurus reproduced by laying eggs. 

Although paleontological expeditions revealed specimens of embryonic age and eggshells, the reproductive behavior of Dryosaurus is poorly studied.

Dryosaurus standing proud
Dryosaurus standing proud | Cyrannian via JWEFandom

Moreover, since few fossilized eggs and nesting sites were associated with ornithopods, it’s quite challenging to at least suspect and suggest specific nesting and incubating behaviors.

It is known that many dinosaurs dug nests in the ground, laid their eggs there, and then covered them with vegetation and dirt. 

However, we cannot confirm this is true for the Dryosaurus.

Additionally, if we were to guide ourselves by what is known about dinosaur hatchlings, we may say that the Dryosaurus babies were precocial since most baby dinosaurs were precocial.

If this were true, then Dryosaurus hatchlings could fend for themselves from the very first hours of their lives.

On the other hand, a nesting ground associated with the Maiasaura, a hadrosaurid ornithopod, showed that these dinosaurs cared for their young for long periods after hatching. 

Again, it remains unknown how much parental care the Dryosaurus exhibited.

Evolution and History

Illustration of Dryosaurus ornithopod dinosaur
Illustration of Dryosaurus ornithopod dinosaur | Dorling Kindersley via GettyImages

The Dryosaurus was an ornithischian ornithopod. 

The clade Ornithopoda was coined in 1881 by the famous Othniel Charles Marsh. 

This group was considered sister to Theropoda, Stegosauria, and Sauropoda

Today, the Ornithopoda is considered a suborder of the Ornithischia order, although this classification has been repeatedly debated.

If we move down the cladogram, we notice that the Dryosaurus is further classified into the Dryosauridae family of the Iguanodontia clade.

Samuel Wendell Williston was the first to make a major paleontological discovery associated with Dryosaurus

In 1876, he discovered some remains in Albany County, Wyoming, attributed to small euornithopods.

Years later, these fossils were associated with Laosaurus altus. In 1894, however, Othniel Charles Marsh, who was the one to name the Ornithopoda group, renamed the genus, calling it Dryosaurus

This name was inspired by the presumable forest-dwelling lifestyle of this creature, which is why the Dryosaurus is now often referred to as the tree lizard.

D. elderae holotype skeleton
D. elderae holotype skeleton (front) with Ceratosaurus at Carnegie Museum | Kordite via Wikipedia CC BY 2.0

The holotype of the genus was recovered from the Morrison Formation. 

It was followed by many other discoveries, which revealed several fragmentary skeletons belonging to juveniles. 

One of the sites bearing much information about the Dryosaurus was close to Uravan, Colorado. 

It was unintentionally found by Rodney D. Scheetz and revealed at least eight specimens of various ages – from embryonic to juvenile individuals.

In 2010, some fossils discovered in Utah were attributed to a second species in the genus, Dryosaurus elderae

However, details about this species are scarce, and how much it differed from the type species is unknown.

Some remains from the Lourinha Formation in Portugal were associated with Dryosaurus but weren’t fully confirmed to belong to the genus. 

Therefore, its location on the prehistoric European continent requires further proof.

Interactions with Other Species

Dryosaurus walking on its two feet
Dryosaurus walking on its two feet | Cyrannian via JWEFandom

Since it hasn’t been fully confirmed that the Dryosaurus lived in Portugal, we’ll only focus on what other creatures lived in the Morrison Formation.

If you have ever wondered what dinosaurs and other creatures the Dryosaurus interacted with, check out our list! 

There’s no confirmation as to whether they did cross paths and, if they did, to what extent.

Here are some prehistoric animals that were contemporary with Dryosaurus and lived in the same habitat:

  • Amphibians like frogs, salamander-like creatures, and toads
  • Sphenodonts
  • Snakes like the Diablophis
  • Lizards like the Dorsetisaurus
  • Turtles like Dinochelus and Glyptops
  • Crocodylomorphs and other reptiles
  • Pterosaurs like Comodactylus and Utahdactylus
  • Various mammaliaforms
Dryosaurus models
Dryosaurus models | Ala z via Wikimedia Commons

Everything was clear until now. The ecosystem was undoubtedly rich enough to ensure that its inhabitants were thriving. 

But what about dinosaurs? After all, the Dryosaurus likely interacted most with others of its kind, not with amphibians or mammals.

Well, the Morrison Formation is one of the most fertile sources of dinosaur fossils. 

Listing every genus discovered there would take days! 

This indicates that if the Dryosaurus was at least a little social, it probably never got bored! 

There’s no doubt that, during its daily walks, it greeted many other dinosaurs. 

Whether they were friendly, as in herbivores, or enemies, as in carnivores, it’s for you to guess!

It is well-known that the Morrison Formation was once home to a myriad of herbivorous ornithischians, including Camptosaurus, Alcovasaurus, Nanosaurus, and Uteodon

Stegosaurus, also an inhabitant of the Morrison Formation
Stegosaurus, also an inhabitant of the Morrison Formation | Daniel Eskridge via iStock

The famous Stegosaurus was also an inhabitant of the Morrison Formation, and many specimens were recovered from the Brushy Basin, where Dryosaurus fossils had been deposited as well.

Sauropods were quite common, too. 

It is believed that sauropods dominated the territory. 

Some of the largest sauropods ever known were among them, such as the Apatosaurus, Amphicoelias, and Diplodocus.

Let’s not forget about the ferocious theropods! Ceratosaurus, Torvosaurus, Allosaurus, and Saurphaganax were only a few, and all were excellent predators! 

The Saurphaganax, for example, is considered the largest terrestrial carnivore of the Late Jurassic living in North America.

Unluckily for them, Dryosaurus ornithopods were probably often preyed upon by these large carnivores. 

Smaller theropods may have preyed upon these tree lizards, too, as they’re known to have developed efficient hunting techniques.

On the other hand, the Dryosaurus probably coexisted in peace with other herbivores, maybe with small exceptions. 

Scientists believe these herbivores had different feeding techniques, adaptations, and specializations, thus allowing them to thrive in the same habitat.

Cultural Significance

Beneski Museum of Natural History Dryosaurus altus
Beneski Museum of Natural History Dryosaurus altus | Richard Haddad via Wikipedia CC BY 2.0

Considering how poorly this creature is known, it’s no surprise that the scientific universe and the media didn’t grant the Dryosaurus the attention it deserved.

It is undoubtedly a remarkable genus in the Ornithopoda clade. 

Further studies on its lifestyle and behavior can shed light on certain ornithischian traits and how our world functioned during the Late Jurassic.


The Dryosaurus was an ornithischian ornithopod classified as an iguanodont. 

It lived in North America (and possibly Portugal) 155-145 million years ago. 

As such, it was an inhabitant of our planet during the Late Jurassic, when it roamed its ecosystem’s forests and looked for suitable vegetation to feed on.

Although quite small, the Dryosaurus was an excellent runner. 

This ability helped it escape multiple predators, probably laughing at its unsuccessful attempt to kill it!

Even though the genus is known from numerous individuals, most are juveniles. 

Therefore, many aspects regarding its appearance, size, and behavior will remain a mystery until further findings are made.


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