The Dinosaurs of Dinosaur

The dinosaurs that Dinosaur National Monument is most known for lived in the Late Jurassic Period, about 150 million years ago.

NPS / Bob Walters and Tess Kissinger

In a time before grass and flowers, before bees and butterflies, and even before the Rocky Mountains rose, dinosaurs called this place home. The ground shook under the footsteps of massive sauropods, like Apatosaurus. Smaller ornithischian dinosaurs browsed low-lying plants, and predatory theropods watched from afar. In the Late Jurassic Period, the Morrison ecosystem of northeastern Utah was home to a large, flat floodplain. This was still the middle age of the dinosaurs. It would be another 84 million years before an asteroid strike rendered all large dinosaurs extinct. Instead, the dinosaurs of the Carnegie Quarry faced different challenges, like drought and predation. Today, their fossilized remains can still be viewed and studied in the context of their original burial site at the Quarry Exhibit Hall.

 

 

 

The Morrison Ecosystem

The dinosaurs of the Carnegie Quarry were found in the Brushy Basin member of the Morrison Rock Formation. Today, that rock layer is made of sandstone, but back in the Late Jurassic Period (about 150 million years ago), it was just sand. At that time, northeastern Utah was home to a vast, flat floodplain. Fossilized unionid clams in the rock layer provide evidence that a system of braided freshwater rivers flowed through this area. Fossilized cycads and ferns indicate that the climate was wamer and more humid than it is today. Dinosaurs roamed the landscape, but they weren't alone. Mixed among the huge bones, scientists have found evidence of the dinosaurs' contemporaries, who shared their lush habitat. These included frogs, salamanders, crocodilians, turtles, and even small mammals.

 

Types of Dinosaurs

Dinosaur National Monument was home to many kinds of dinosaurs. All dinosaurs are traditionally grouped into two categories. There's the ornithischians, which means "bird hipped," and the saurischians, which means "lizard hipped." Ornithischians feature a hip structure resembling that of modern-day birds, where both the pubis and ischium bones point backward at a slightly downturned angle. Saurischians, on the other hand, tend to have hips that resemble those of modern-day lizards. In saurischians, the pubis bone usually points forward and down. All sauropods and theropods belong to the saurischian order of dinosaurs, even though some theropods did evolve a more bird-like hip structure later on. The interactive image below shows the difference between saurischian "lizard-like" hips and ornithischian "bird-like" hips. Drag the middle arrow up and down to see each hip type.

 

Top image
Saurischian dinosaurs were named for their hip structure, which resembles that of modern-day lizards. The ancestor of all saurischian dinosaurs had a pubis bone that pointed forward and down between the legs.
Credit: NPS / Molly Swindle

Bottom image
Ornithischian dinosaurs have a hip structure resembling that of modern-day birds. The common ancestor of all ornithischian dinosaurs had a pubis and ichium bone that pointed backward, toward the tail.
Credit: NPS / Molly Swindle

 

Sauropods are long-necked, long-tailed dinosaurs with 4 pillar-like legs. They ate plants.

NPS / Molly Swindle

Sauropods

When most people think of a dinosaur, they picture a huge plant-eating reptile with a long neck, long tail, and 4 pillar-like legs. Dinosaurs that meet this description are almost always members of the sauropod group. All sauropods belong to the saurischian (lizard hipped) order of dinosaurs. Sauropods are the most common type of dinosaur found in the Carnegie Quarry. Because they were so big and sturdy, their bones were much more likely to survive the fossilization process than those of smaller, frailer animals. The Quarry Exhibit Hall contains the fossilized remains of several Late Jurassic sauropods. These were Apatosaurus, Camarasaurus, Diplodocus, and Barosaurus.

 

Theropods walk on two legs and have clawed arms. Usually, they were sharp-toothed meat eaters, but some ate plants. Modern day birds are thought to have descended from theropod dinosaurs, and are still grouped in that family today.

NPS / Molly Swindle

Theropods

Like sauropods, theropods are also members of the saurischian (lizard hipped) order. When you think of a vicious meat-eating dinosaur, you're most likely thinking of a theropod. These dinosaurs usually walked on two legs and had small arms. Most of them were sharp-toothed meat eaters, but there were a handful who ate plants. Scientists found 3 types of meat-eating theropods in the Carnegie Quarry: Allosaurus fragilis, Ceratosaurus, and Torvosaurus tanneri. Another kind of Allosaur (Allosaurus jimmadseni) was found in a rock layer about 5 million years older than the other Quarry dinosaurs. Scientists have found so many theropods fossilized with evidence of feathers that it's believed most theropods had feathers at some point in their life.

 

Ornithischian dinosaurs (like this Stegosaurus) often had beaks. Many developed interesting body structures, like crests, horns, spikes, or quills.

NPS / Molly Swindle

Ornithischians

Pretty much any dinosaur that isn't a sauropod or theropod belongs in the ornithischian group. It's thought that the ancestors of ornithischian dinosaurs split from the ancestors of saurischians sometime in the Triassic period (235-240 million years ago). Eventually, the saurichian group split further into sauropods and theropods. Many ornithischian dinosaurs had beaks. Some developed huge crests which helped to amplify noises. Others developed unique forms of defense, like horns, spikes, or quills. The Quarry Exhibit Hall contains 3 species of ornithischian dinosaur. These are Stegosaurus, Dryosaurus, and Camptosaurus.

 

Wait... Aren't Birds Dinosaurs Too?

Scientifically, yes! All modern-day birds are considered avian (bird) dinosaurs. Scientists believe they descended from a group of theropods called "maniraptorans." Despite having literal bird hips, birds are actually grouped with saurischian (lizard hipped) dinosaurs. In cladistics, the science of how organisms are related, ancestry is more important than appearance. The fossil record shows that some theropods developed their bird-like hips independently, long after the saurischian-ornithischian split. The names are confusing because scientists named dinosaur groups based on hip-shape before they realized that birds are dinosaurs, too. 

 

Quarry Dinosaurs

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  Dinosaurs

  Apatosaurus louisae

  Apatosaurus louisae was the biggest dinosaur of the Morrison ecosystem.

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  Dinosaurs

  Camarasaurus lentus

  Camarasaurus lentus was the most abundant large dinosaur found in the Carnegie Quarry.

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  Dinosaurs

  Diplodocus longus

  Diplodocus was the longest dinosaur in the Morrison ecosystem, measuring up to 92 feet (28 m) from head to tail.

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  Dinosaurs

  Barosaurus lentus

  Barosaurus had a neck that was longer than the length of its tail.

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  Dinosaurs

  Allosaurus fragilis

  Allosaurus fragilis was the most common large predator of the Morrison ecosystem.

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  Dinosaurs

  Ceratosaurus

  The presence of Ceratosaurus is only known at the Carnegie Quarry thanks to a few small, but very distinctive bones.

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  Dinosaurs

  Torvosaurus tanneri

  Torvosaurus tanneri was the largest predatory dinosaur found in the Carnegie Quarry.

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  Dinosaurs

  Camptosaurus aphanocetes

  Camptosaurus is one of the smaller plant-eating dinosaurs found in the Carnegie Quarry.

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  Dinosaurs

  Dryosaurus elderae

  Dryosaurus is the smallest plant-eating dinosaur found at the Carnegie Quarry.