Fossils and Paleontology

Without a doubt, Allosaurus was the single most terrifying predator to roam the Late Jurassic floodplains. Allosaurus grew to be 30 feet long and was the most common meat eating dinosaur of the Jurassic Period. Its head, over two feet long, contained dozens of sharp, serrated teeth. Its arms were muscular and ended in three huge, sharp, powerful talons. Allosaurus preyed upon all sorts of animals, from small two-legged plant eaters to armored Stegosaurus and the massive sauropods like Apatosaurus. Here in western Colorado, we have lots of specimens of Allosaurus, most of which come from our public lands. It is in fact the most common dinosaur we find at the Mygatt-Moore Quarry in Rabbit Valley.

Length: Up to 30 feet in length

Weight: Up to 1.5 tons

Age: 152 million years ago

Diet: Other Dinosaurs

Click on the pictures below to find out what each fossil is.

Apatosaurus is one of the most famous dinosaurs ever discovered. For many years there were two similar dinosaurs that were recognized by the public; Apatosaurus and Brontosaurus. In 1901, Paleontologist Elmer Riggs from Chicago’s Field Museum was hunting for dinosaurs right here in Colorado’s Grand Valley. When he found a skeleton going into a cliff at what is now Dinosaur Hill, a site managed by the BLM in Fruita, Riggs realized that he had found something special. Riggs finally published his findings. Apatosaurus and Brontosaurus were not different animals at all, but instead were the same genus. Since Apatosaurus had been named first, it stayed Apatosaurus and the name Brontosaurus was sent to the history books.

Length: Up to 80 feet in length

Weight: Up to 17 tons

Age: 152 million years ago; Late Jurassic Period

Diet: Plants, especially low-rowing ferns, horsetails, and other ground cover.

Click on the pictures below to find out what each fossil is.

Camarasaurus has a skull adapted to eating plants. The broad, spoon-shaped teeth would not have been good at slicing up meat. Indeed, they would not have worked well for processing small plants either. With its long neck and big, blunt teeth, Camarasaurus was probably best suited for pulling off larger parts of trees. Although sauropods couldn’t chew (something that Jurassic Park got wrong), they may have had “stomach stones” similar to some birds today that would help them mash up and digest plant matter. This dinosaur is one of the most common dinosaurs we find in the Late Jurassic Morrison Formation.

Length: Up to 60 feet in length

Weight: Up to 45 tons

Age: 152 million years ago; Late Jurassic Period

Diet: Plants; it was a generalist, so it likely was able to eat whatever sort of plants happened to be available.

Click on the pictures below to find out what each fossil is.

The Ceratosaurus was a medium sized carnivore and is named for the horn on the end of its skull. Ceratosaurus means horned lizard. It’s dinosaur classification lands it in the Theropod family.  It lived in the later Jurassic period and grew up to 20 feet long. Despite its smaller size, it would have been Allosaurus’s main rival. It had a strong jaw and teeth like blades that were used for ripping away meat from its prey.

Length: Up to 20 feet in length

Weight: Up to 980 Kg (a small car)

Age: 152 Million years ago; Late Jurassic Period

Diet: Other Dinosaurs

Click on the pictures below to find out what each fossil is.

This is Fruitadens, a dinosaur found only in Fruita! It also happens to be the smallest plant-eating dinosaur yet discovered. Fruitadens was as small as plant-eating dinosaurs got, weighing only about 1 pound. Only its contemporary from Germany, Compsognathus, a meat-eater, got as small. Fruitadens and Compsognathus are tied for the honor of Smallest Dinosaur In The World. Compare this to some sauropod dinosaurs from the same rocks, such as Apatosaurus, which may have weighed as much as 75,000 pounds! Fruita has other fossil animals from the Morrison Formation named after it as well, including Fruitachampsa (a fossil crocodile) and Fruitafossor (a fossil mammal).

Length: Up to 3 feet in length

Weight: Up to 1 pound

Age: 150 million years ago; Late Jurassic Period

Diet: Plants and bugs

The majority of the fossils that are found in the Grand Valley are found in what is called the Morrison Formation.

Mymoorapelta was first found at the Mygatt-Moore Quarry, located in Rabbit Valley just outside of Fruita. Mymoorapelta is one of the rarest dinosaurs from the Mygatt-Moore Quarry, with only the remains of two individuals being discovered so far. Related to other famous dinosaurs like Ankylosaurus, Mymoorapelta is the oldest ankylosaur discovered anywhere in the world! Named in 1994 by scientists from Colorado and Utah, Mymoorapelta changed what scientists thought they knew about armored dinosaurs. These fossils represent the first and/or best example of this animal yet found! Mymoorapelta was the first Jurassic genus of ankylosaur (armored dinosaur) found in North America.

Length: Up to 15 feet in length

Weight: Up to 1,000lbs

Age: 152 million years ago; Late Jurassic Period

Diet: Plants, especially low-growing ferns and horsetails

Click on the pictures below to find out what each fossil is.

Stegosaurus is Colorado’s state fossil (declared by the governor in 1982 ). Stegosaurus fossils have been found across western Colorado, including just west of Grand Junction. Stegosaurus was equipped with fearsome spikes on its tail, which could be used to drive off predators. Some of the tail spikes from a Stegosaurus found in Rabbit Valley are on display in Fruita’s Dinosaur Journey museum. Although Stegosaurus is best known and recognized for its large plates that run down its spine (the name Stegosaurus means “roofed lizard” after all), we still aren’t really sure what their purpose was. Defense? Display? Something else? We hope that future specimens can help solve this mystery.

Length: Up to 30 feet in length

Weight: Up to 7 tons

Age: 155 million years ago; Late Jurassic Period

Diet: Plants, especially low-growing ferns and horsetails, and other ground cover.