An Ultimate Guide to Tenontosaurus: The Sinew Lizard

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Name MeaningSinew LizardHeight1.8 to 2.4 meters (6 to 8 feet)
Pronunciationteh-NON-toh-SAW-rusLength6 to 7 feet (20 to 23 feet)
EraMesozoicEarly CretaceousWeight0.5 to 1 metric ton (1,300 to 2,200 lbs)
ClassificationDinosauria,‭ ‬Ornithischia & OrnithopodaLocationNorth America (USA) and Canada

Tenontosaurus Pictures

Tenontosaurus was an ornithopod herbivorous dinosaur that lived in North America during the Cretaceous Period | CoreyFord via GettyImages

The Tenontosaurus

Gage Beasley Prehistoric's Tenontosaurus Concept
Gage Beasley Prehistoric’s Tenontosaurus Concept

Also known as the sinew lizard, the Tenontosaurus is a genus of ornithopod dinosaurs that lived in North America during the Early Cretaceous period about 115 to 108 million years ago.

The sinew lizard is known for its long and muscular tail, which takes up more than half its entire body length.

The dinosaur’s scientific name, which was assigned by Barnum Brown (and later modified by John Ostrom), was a reference to this powerful tail.

The first Tenontosaurus fossils were discovered in 1903, and since then, two species have been identified in the genus.

Several specimens of this dinosaur have been discovered in various geological formations across North America.

The widespread distribution of this dinosaur fossil suggests that it was quite abundant on the continent during the Early Cretaceous period.

In this post, we’ll cover some of the most interesting facts about this dinosaur, including its physical characteristics, habitat and distribution, behavior, lifecycle, and interaction with other dinosaur species.

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

Tenontosaurus was an ornithopod herbivorous dinosaur that lived during the Cretaceous Period of North America | CoreyFord via GettyImages

The Tenontosaurus was a medium to large-sized ornithopod dinosaur known to have grown to lengths of about 20 to 23 feet (6 to 7 meters).

Estimates of this dinosaur’s weight range from a low of 1300 pounds to as high as 2200 pounds (600 to 1000 kg).

Tenontosaurus may have stood around 6 to 8 feet (1.8 to 2.4 meters) tall at the hip, with its head and neck extending several more feet above that height.

The most striking feature of this dinosaur was its unusually long and broad tail which was made up of a network of bony tendons.

The dinosaur’s genus name and nickname (sinew lizard) is a reference to this long tail and its network of tough fibrous tissue. 

Gage Beasley Prehistoric's Tenontosaurus Size Comparison
Gage Beasley Prehistoric’s Tenontosaurus Size Comparison

The Tenontosaurus back was also supported by bony tendons.

This made it possible for the dinosaur to carry its tail erect off the ground.

Due to its long forelimbs and strong finger bones, scientists believe that this dinosaur was quadrupedal.

However, it may have also used its tail as a sort of counterbalance, making it possible to stand up on its hind legs alone while feeding. 

The sinew lizard had a long flexible neck with a prolonged, laterally compressed skull.

It had strong, serrated, teeth suitable for grinding up plant materials.

However, the front end of its mouth had no teeth. Instead, this part had a horny beak, a common feature in many herbivorous dinosaurs.  

The body of the Tenontosaurus was covered in scaly skin, and it had a row of bony plates running down its back.

The Tenontosaurus’ long, powerful arms had three-fingered hands that were equipped with sharp claws, which it may have used for defense or foraging. 

Habitat and Distribution

Fossils of the two species of dinosaurs in this genus (Tenontosaurus tilletti and Tenontosaurus dossi) have been collected from several locations throughout North America.

In fact, at least 60 specimens have been recovered so far in Western North America, which suggests that the dinosaur was a common sight in this part of the continent during the Cretaceous period. 

Scientists discovered the first sinew lizard fossil in Big Horn County, Montana, back in 1903.

They have also found fossils of this dinosaur in Wyoming, Oklahoma, Texas, Idaho, Utah, and Maryland.

The majority of Tenontosaurus fossils have been found in the Western Interior region of North America.

This suggests that the dinosaur’s range was limited to this part of the continent.

Paleoecological studies suggest that when Tenontosaurus first emerged in the Wyoming and Montana area, the region had a dry, semi-arid climate, experiencing periodic droughts and seasonal rainfall.

However, over the next few million years, the environment changed to a more tropical climate similar to present-day Louisiana.

Increased rainfall in the region gave rise to flood plains, swampy inlets, and river deltas.

Despite the dramatic change in climate, the population of Tenontosaurus in the region experienced an increase rather than a decrease. This trend suggests that the dinosaur was quite adaptable.

Behavior and Diet

Tenontosaurus was an ornithopod herbivorous dinosaur that lived in North America during the Cretaceous Period | CoreyFord via GettyImages

Tenontosaurus was an herbivorous dinosaur, meaning it survived entirely on a plant-based diet.

The ecosystem in Western North America, where this dinosaur lived in the Early Cretaceous, had an abundance of tree ferns and cycads.

There may have been a few primitive flowering plants in this region as well. 

Because this dinosaur most likely walked on all fours (quadrupedal), evidence suggests that it was a low browser.

Tenontosaurus dinosaurs (especially juveniles) would have fed on low-growing shrubs and ferns.

However, thanks to their muscular tails, adults were capable of adopting a bipedal stance.

This would raise their browsing height to about 10 feet, allowing them to access taller trees for food. 

The sinew lizard had a strong and powerful U-shaped beak with an angled cutting surface.

This and their tightly packed serrated teeth allowed them to consume different parts of vegetation, including the leaves, fruit, and even wood. 

There is currently no direct evidence to suggest that Tenontosaurus was a social dinosaur.

Mounted skeletons of an adult with juveniles at the Sam Noble Oklahoma Museum of Natural History
Mounted skeletons of an adult with juveniles at the Sam Noble Oklahoma Museum of Natural History | Vince Smith via Wikipedia CC BY-SA 2.0

However, some indirect evidence suggests that it may have lived in herds or at least congregated in groups for short periods.

Fossil evidence of multiple individuals of Tenontosaurus found together in the same location indicates that they may have lived together in small groups.

Scientists have also found some Tenontosaurus trackways, which suggests that multiple individuals were moving together.

However, it is also possible that these groupings were simply the result of temporary congregations at water sources or feeding areas rather than evidence of true social behavior.

Being a herbivore with limited defenses would have put this dinosaur at the mercy of predators.

However, the Tenontosaurus had powerful hind legs and a long, stiff tail that made it a fast and agile runner.

This adaptation would have made it easier to escape from predators such as Deinonychus and Acrocanthosaurus

Life Cycle

Tenontosaurus was an ornithopod herbivorous dinosaur that lived in North America during the Cretaceous Period | CoreyFord via GettyImages

Like several other dinosaurs, scientists have discovered medullary bone tissue on the femurs of many Tenontosaurus fossils.

This is a tissue only found in present-day egg-laying birds.

Medullary bone is a specialized bone tissue formed in female birds when calcium is mobilized from the skeleton to form eggshells during egg-laying cycles.

The presence of medullary bone tissue in the fossilized femurs of Tenontosaurus dinosaurs provides conclusive evidence that this dinosaur laid eggs.

Reconstructed skeleton of Tenontosaurus
Reconstructed skeleton of Tenontosaurus, from the Cloverly Formation. | Rodney via Wikipedia CC BY 2.0

Additionally, the Tenontosaurus fossil with this medullary tissue had an estimated age of about eight years old before its death.

This suggests that the dinosaurs reached reproductive maturity at an early age. 

Scientists believe that the sinew lizard grew quickly and attained maturity early in life.

However, once at full maturity, the rate of growth and development would slow down.

This is the opposite of the observed pattern in several other iguanodontian dinosaurs.  

Evolution and History

Tenontosaurus was an ornithopod herbivorous dinosaur that lived in North America during the Cretaceous Period | CoreyFord via GettyImages

Their evolutionary history can be traced back to the Late Jurassic period, about 150 million years ago, when the first ornithopod dinosaurs appeared.

Ornithopods were a group of herbivorous dinosaurs that were among the most dominant and the most successful dinosaur groups of the Mesozoic era. 

Over the next several million years, ornithopods would evolve into different forms, which included both bipedal and quadrupedal varieties.

Many of them were characterized by specialized beaks and teeth modified for eating different types of vegetation. 

The Tenontosaurus is a member of the iguanodontid family, which was a group of herbivorous ornithopods popular for their long, powerful hind legs, spiked thumbs, and ability to run very quickly.

The discovery of Tenontosaurus has provided important insights into the evolutionary history of iguanodontids.

For example, Tenontosaurus had a large thumb spike on its hand, which was likely used for defense against predators.

Iguanodon | janzwolinski via GettyImages

This is a feature seen in many other iguanodontid dinosaurs like the Iguanodon and Ouranosaurus, suggesting that it was an important adaptation for this group of dinosaurs.

In addition to its thumb spike, Tenontosaurus also had a unique feature called a hypapophysis, seen in a few ornithopod dinosaurs.

The hypapophysis is a projection on the underside of the dinosaur’s vertebrae, but scientists are not exactly certain of its function.  

Interactions With Other Species

Tenontosaurus got attacked
A pack of Deinonychus dinosaurs attack a Tenontosaurus during the Cretaceous Period of North America | CoreyFord via Getty Images

They shared their paleo-environment with the Deinonychus, a common carnivorous dinosaur that lived during the Early Cretaceous.

A few indeterminate species of allosauroid theropods and goniopholid crocodiles were also found in the same habitat. 

As the climate changed in North America during the mid-Albian age of the Cretaceous period, many more dinosaurs moved to the region.

Some of them include the Zephyrosaurus (an ornithopod dinosaur), the Microvenator (a type of oviraptor), and a few indeterminate species of sauropod and ornithomimids.

However, the Tenontosaurus remained the most dominant herbivore in the region. 

The presence of teeth marks on their bones and the discovery of many Deinonychus fossils in locations where the Tenontosaurus was abundant suggests that the carnivore most likely hunted the sinew lizard.

Acrocanthosaurus atokensis was another massive predator found in the same paleo-environment, and it may have hunted the Tenontosaurus as well. 

Other vertebrates that lived alongside the Tenontosaurus include a few primitive mammals, reptiles like Atokasaurus metarsiodon, cartilaginous fish such as Hybodus, and turtles such as Glyptops.

Cultural Significance

Tenontosaurus Concept from Jurassic Fight Club | Vaderxl via Jurassic Fight Club Fandom

Due to the abundance of fossils, they are a relatively well-known dinosaur among paleontologists and dinosaur enthusiasts.

Perhaps the most significant contribution of this dinosaur to paleontology is the discovery of medullary bones in its femur. 

This discovery provides some important insights into the reproductive biology of Tenontosaurus and dinosaurs in general.

It has also helped scientists draw an evolutionary link between modern birds and ancient dinosaurs. 

The Tenontosaurus was featured in the paleontology-based TV Series — Jurassic Fight Club.

The show showcased hypothetical prehistoric battles between different types of dinosaurs, and in one episode, the Tenontosaurus was pitted against a pack of Deinonychus.

Tenontosaurus has also been a prominent figure in several toy lines. 


Tenontosaurus was a medium-sized dinosaur that lived approximately 115 to 108 million years ago.

The quadrupedal dinosaur was known for its powerful hind limbs and muscular tail, after which it was named.

It was an herbivore adapted to survive in a wide range of environments.

It fed on cycads and ferns using its sharp beak and strong teeth. 

Tenontosaurus lived in Western North America during a period of major climatic change but were well adapted to survive as the region changed from an arid to a subtropical climate.

It is quite abundant in the fossil record, with up to 60 fossils discovered so far.

The paleontological study of this dinosaur’s fossil provides some insight into the reproductive life cycle of the dinosaurs and their link to modern birds.  


What does the name “Tenontosaurus” mean?

The name “Tenontosaurus” means “sinew lizard.”

It is a reference to the tough fibrous tendons that support the dinosaur’s tail and back.

American paleontologist, Barnum Brown, gave the dinosaur this name in 1970. 

Did the Tenontosaurus have any natural predators?

Yes. The Tenontosaurus may have been preyed upon by large theropod dinosaurs such as Acrocanthosaurus or Deinonychus.

These carnivorous dinosaurs were abundant around the same time as the Tenontosaurus, and their fossils have been discovered in the same formations. 

Where have fossils of the Tenontosaurus been found?

Their fossils have been found in various locations throughout North America, including Texas, Oklahoma, Wyoming, and Montana.


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