Dinosaur National Monument (Part 1)

Dinosaur National Monument protects 210,844 acres on the edge of the Uinta Basin along the border of Utah and Colorado. The Utah side features the world-renowned Carnegie Quarry “Wall of Bones” while the Colorado side preserves the canyons around the confluence of the Green and Yampa Rivers. Quarry Visitor Center is near Jensen, UT while Canyon Visitor Center is near Dinosaur, CO.

This Stegosaurus statue outside of Quarry Visitor Center is one of nine life-sized dinosaurs sculpted by Louis Paul Jonas for the Sinclair Dinoland exhibit at the 1964-1965 New York World’s Fair. After the fair, the dinosaurs were transported and displayed around the country until the late 1960s. Since then, this Stegosaurus has resided at Dinosaur National Monument, first at Carnegie Quarry and now at the visitor center.

Paleontologist Othniel Charles Marsh described the first Stegosaurus in 1877 based on a few bone fragments found near Morrison, CO. This incited the Bone Wars, or Great Dinosaur Rush, a 15-year period of ruthlessly competitive fossil hunting and discovery in the western United States between Marsh and rival paleontologist Edward Drinker Cope. The plates and spikes of Stegosaurus initially confused the scientific community and their accepted arrangement on the animal evolved as more information was gathered. Subsequent fossil discoveries at multiple locations, including Carnegie Quarry, eventually provided enough information to reconstruct a complete skeleton.

Over 800 paleontological sites have been discovered in Dinosaur National Monument and fossils of at least 13 dinosaur species have been found within its boundaries. Carnegie Quarry alone yielded fossils of Apatosaurus louisae, Allosaurus fragilis, Stegosaurus ungulates, Diplodocus hallorum, Camarasaurus lentus, Camptosaurus aphanoecetes, Dryosaurus elderae, Ceratosaurussp., Torvosaurus tanneri, and Barosaurus lentus. The quarry also preserved fossils of Vetulonaia sp. mussels, four reptiles, including Glyptops plicatus, Dinochelys whitei, Opisthias rarus, and Goniopholissp., unidentified fragments of fossilized wood, and unidentified insect burrows in dinosaur bones. Fossils discovered elsewhere in the monument include those of the dinosaurs Abydosaurus mcintoshi, Allosaurus jimmadseni, and Deinonychus sp., the reptile Hoplosuchus kayi, the amphibians Iridotriton hechti and Rhadinosteus parvus, and the mammal Glirodon grandis. Several specimens found in the monument became the holotypes of their species, meaning that they were the first found and scientifically described, including those of Apatosaurus louisae, Camptosaurus aphanoecetes, Dryosaurus elderae, Abydosaurus mcintoshi, Allosaurus jimmadseni, Dinochelys whitei, Hoplosuchus kayi, Iridotriton hechti, Rhadinosteus parvus, and Glirodon grandis.

Dinosaur National Monument boasts the most complete geologic record in the National Park System, containing 23 exposed rock layers deposited over about 1.1 billion years. Only the Ordovician, Silurian, and Devonian layers are missing. The primary fossil-bearing layer is the Morrison Formation which is composed of multicolored sedimentary rocks formed from stream and floodplain deposits during the Late Jurassic. 

During the Late Jurassic, Carnegie Quarry was likely located at a bend or sandbar in a river where the bones of dinosaurs and other ancient animals collected following flash floods. Continuous deposition of sediments by the river quickly buried the bones before they could decay. The dinosaurs are believed to have died along the shore or in dry sections of the river during droughts over time rather than in one incident. Excavations uncovered some bones that were articulated, or connected as they would have been in life, and others that were disarticulated, supporting the argument that the dinosaur remains were in varying states of decay by the time they were buried.

Fossils of Vetulonaia sp. mussels reveal that this area underwent three severe droughts during the Late Jurassic. These mussels belong to the family Unionidae and can only survive in moving water. Unionid mussels typically die with closed shells after being buried alive by river sediment or with open shells when water is absent. Paleontologists identified at least three instances where many mussels fossilized with open shells, suggesting that large portions of the river dried up during those periods.

The bones at Carnegie Quarry were fossilized via permineralization. This means that slightly acidic water continuously dissolved minerals in river sediments and percolated into the spongy bones where the minerals were deposited in pores, forming an internal cast. Bacteria transported by the water then ate away the bones while producing calcium carbonate which eventually permeated the bone cells and formed a hard shell, completing the fossilization.

Around 70-50 million years ago, a series of mountain-building events in North America called the Laramide orogeny formed the Uinta Mountains to the northwest uplifting and folding the rock layers of Dinosaur National Monument into an anticline, or hill shape. Millions of years of erosion eventually removed the top of the anticline and exposed the fossil-bearing Morrison Formation.

The turn of the 20th century brought the Second Jurassic Dinosaur Rush, a period in which several museums competed to find and display the largest dinosaurs. The American Museum of Natural History, Carnegie Museum of Natural History, Field Columbian Museum, and Universities of Wyoming and Kansas each funded efforts to discover and exhibit impressive dinosaur fossils. In 1909, the Carnegie Museum, founded and financed by industrialist Andrew Carnegie, directed paleontologist Earl Douglass to search for dinosaur fossils in northeastern Utah. While exploring the hills along the Green River, Douglass found eight vertebrae of an Apatosaurus, the first of many dinosaur fossils discovered at the new Carnegie Quarry. Excavation revealed the vertebrae to be part of the most complete Apatosaurus skeleton ever discovered. In 1915, President Woodrow Wilson proclaimed 80 acres surrounding Carnegie Quarry as Dinosaur National Monument.

Carnegie Quarry was established in the Brushy Basin Member of the Morrison Formation, which includes layers of volcanic ash mixed into the stream and floodplain deposits. Radiometric dating of the ash and crystals inside it combined with magnetostratigraphy revealed fossils from the quarry were deposited about 150.91-150.04 million years ago. Earl Douglass led excavations at the quarry, extracting over 350 tons of fossils originating from almost 400 individual dinosaurs representing 10 species. Early on, fossils were packed in wooden crates, moved down the mountain on mules and horses, ferried over the Green River, and transported via mule cart for 60 miles to Dragon, UT. From there, they were transferred to boxcars, hauled another 60 miles over Baxter Pass, loaded on Denver and Rio Grande standard gauge cars, and finally shipped to the Carnegie Museum in Pittsburgh, PA for study and display. In 1922, the museum relinquished its claim to operate the quarry, but Douglass continued to work there alongside the National Museum and University of Utah until all excavation ceased in 1924 and he resigned from the Carnegie Museum.

Fifteen years of excavation had seen a section of rock about 600 feet long and 40 feet high removed from Carnegie Quarry, but part of the ridge was left intact for future development. Between 1933-1938 the Civil Works Administration and then the Works Progress Administration employed men to build a road to the quarry, remove rock and sediments covering the fossil-bearing layer, and construct a temporary museum. World War II interrupted the work but about 10 feet of clay overburden was left to protect the fossils. In 1938, President Franklin Delano Roosevelt greatly expanded the boundaries of Dinosaur National Monument to 210,844 acres encompassing the canyons of the Green and Yampa Rivers along the Utah-Colorado border.

In 1951, a small tin shelter was erected over the east side of the quarry and the following year excavations resumed with the intent of exposing fossils in situ, or in the position of their original discovery. The National Park Service Mission 66 program later funded the construction of a permanent two-story building with natural light for visitors to witness the fossil excavation process. In 1958, Quarry Exhibit Hall became the first site to exhibit fossils in situ for the public, achieving Earl Douglass’ original vision for the quarry.

Quarry Exhibit Hall was constructed on unstable bentonitic soils which caused some columns and walls to crack by 1967. Although the building was designated a National Historic Landmark in 2001, it was closed in 2006 due to major risk of collapse. Administrative functions for the monument were moved to Quarry Visitor Center, which was constructed nearby, and Quarry Exhibit Hall was rebuilt and stabilized until it reopened in 2011.

A tram regularly shuttles visitors between Quarry Visitor Center and Quarry Exhibit Hall. The Modern Quarry, aka "Wall of Bones," exhibits the cliff face of fossils revealed between 1952-1992. The rock layer is tilted 67° and displays over 1,500 fossils from about 100 individual dinosaurs. The Historic Quarry of fossils excavated between 1909-1924 was once much larger and originally held over 5,000 fossils. All fossil locations were recorded on maps and efforts are ongoing to establish an online Digital Quarry. 

Here are a variety of sauropod fossils and casts. Sauropoda is a clade of large, quadrupedal, herbivorous long necked, long tailed, small headed dinosaurs with four pillar-like legs. On the bottom left is a skull cast of the Apatosaurus louisae holotype, on the top right is a cast of a Camarasaurus lentus skin impression, and below that are original fossils of a Camarasaurus lentus tooth and Diplodocus longus teeth.

Apatosaurus louisae is a sauropod species that lived about 152-150 million years ago during the Late Jurassic. A. louisae is the largest dinosaur species known from the monument, averaging about 18.1-24.7 tons, with the largest individuals weighing up to 36 tons. It averaged 69-75 feet long, had single-clawed forelimbs that were slightly shorter than the three-clawed hindlimbs, and held its tail off the ground as it moved. A. louisae was a generalized browser, had a skull similar to Diplodocus, and may have used its tail as a whip for defense, creating loud noises, or as a tactile organ to feel the positions of other individuals moving in the group around it, like other diplodocids. Its vertebrae also featured air sacs that made the bones lighter. The genus was first described in 1877 by Othniel Charles March, who named it Apatosaurus, Greek for "deceptive lizard," because the pairs of bones attached to the vertebrae, called chevrons, appeared unlike those of other dinosaurs. When Earl Douglass discovered the first eight A. louisae vertebrae at Carnegie Quarry in 1909, he initially believed them to belong to a Brontosaurus. However, most paleontologists of the 20th century came to the consensus that Brontosauruswas not different enough from Apatosaurus to warrant its own genus, so the name Apatosaurus took precedent since it was described first. In 1916, after the quarry specimen was determined to be a new species, Carnegie Museum director William H. Holland assigned it the specific epithet louisaeafter Andrew Carnegie's wife, Louise. The only A. louisae skull ever found came from Dinosaur National Monument. 

This Allosaurus fragilis skull is an original fossil discovered at Carnegie Quarry in 1924 by a team from the University of Utah. It has minimal distortion and is one of the best-preserved Allosaurus skulls ever discovered.

Allosaurus fragilisis a theropod species that lived about 155-145 million years ago during the Late Jurassic. Theropoda is a clade of bipedal carnivorous dinosaurs with hollow bones, large three-toed hindlimbs, and shorter three-clawed forelimbs. A. fragilis is the most common theropod species in the monument, representing almost 75% of those found in the Morrison Formation. Adults averaged 28 feet in length, weighed about 1.9 tons, and had serrated teeth up to three inches long as well as a pair of horns over the eyes that may have been used for display, intraspecific combat, or as sunshades. A. fragilis overpowered its prey and preferred hunting in dried floodplains and inland areas, possibly in small groups. The species was first described in 1877 by Othniel Charles March, who named it Allosaurus, Greek for "different lizard," and fragilis, Latin for "fragile," both referring to the lightening features in its vertebrae that were different from other dinosaurs known at the time discovery. A. fragilis is the state fossil of Utah and its likeness is often used in promotional materials for Dinosaur National Monument.

This is a cast skeleton of an Allosaurus fragilis from the Cleveland-Lloyd Quarry in east-central Utah. It is about the same size as the one from Carnegie Quarry whose skull is on exhibit. Allosaurus likely preyed upon large herbivores such as Stegosaurus.

Stegosaurus ungulatusis a thyreophoran species that lived 155-150 million years ago during the Late Jurassic. Thyreophora is a clade of armored ornithiscians and Ornithischia is an order of dinosaurs with bird-like hip structures. S. ungulatus was a large quadrupedal herbivore with a rounded back, short forelimbs, long hindlimbs, and a tail that was held aloft. It could reach 23 feet in length and weigh about 4.2 tons. The species was first described in 1879 by Othniel Charles Marsh, who named it Stegosaurus, Greek for “roof lizard,” andungulatus, Latin for “hoofed,” referring to its feet and the 17-22 diamond-shaped plates along its back. It was the second species of the genus described by Marsh following Stegosaurus armatus in 1877, however, S. armatus would later be considered nomen dubium, a scientific name of unknown or doubtful application. Stegosaurus plates were not directly connected to the skeleton and often separated from the animal after death. Paleontologists initially believed that the plates laid flat over the back but later discoveries of articulated specimens showed that they stood upright. The plates may have been used for temperature regulation, display, or protection from predators. Stegosaurus had four large spikes at the end of its tail, called thagomizers, used for defense against predators. It also had a very small brain in proportion to its body. In 1977, paleontologists excavated the most complete juvenile Stegosaurus fossil from Carnegie Quarry. As it was found without plates, it is unknown if juveniles had them. Many isolated plates and spikes of S. ungulates have been found all over Carnegie Quarry.

Diplodocus longus is a sauropod species that lived 154–152 million years ago during the Late Jurassic. It is one of the most abundant sauropods found in the Morrison Formation and was once thought to be the longest dinosaur. D. longus averaged about 79–85 feet in length but could grow up to 92 feet, and it was light for its size, with an average weight between 13.2–16.3 tons. An Apatosaurus of the same length would weigh nearly twice as much. D. longus had slightly shorter forelimbs than hindlimbs and moved in small herds. The long whip-like tail composed of about 80 vertebrae may have been used for defense, creating loud noises, or as a tactile organ. D. longus had pencil-like teeth in the front of the jaws for stripping leaves and could rear up on its hind legs, likely using its large tail as a tripod, to reach leaves up to 36 feet higher. Partial skin impressions found in 1990 revealed that some diplodocid species had narrow keratinous spines on their tails like iguanas. The spines could reach up to 7.1 inches long and may have grown along the back and neck as well. Othniel Charles March first described the genus in 1878 based on a very incomplete fossil and named it Diplodocus, Greek for “double beam,” and longus, Latin for “long,” referring to its length and the tail vertebrae chevrons, which were thought to be unique. Some paleontologists have suggested that the D. longus type species, or reference specimen with which the genus is associated, lacks features needed to appropriately compare it with other specimens and have labeled it nomen dubium. However, the International Commission on Zoological Nomenclature rejected a proposal to make D. carnegii the new type species and maintained D. longus as the type species. Many more complete fossils are assigned to D. longus, including three of the most complete skeletons found at Carnegie Quarry.