Dinosaurs & Fossils
Dinosaurs lived only during the Mesozoic Era, which is often called the “Age of Dinosaurs.” Utah has perhaps the best Mesozoic rock record in the world. Other Mesozoic fossils found in Utah include remnants of marine and land plants and animals. Utah is also home to Ice Age fossils, tracks and tracksites, petrified wood, and trilobites.
Utah Dinosaurs
A reconstruction of the Stikes dinosaur death trap. Adult and juvenile Utahraptor dinosaurs attack an iguanodont dinosaur trapped in quicksand. By Julius Costonyi.
Dinosaurs lived during the Mesozoic Era, more specifically, the Triassic, Jurassic, and Cretaceous Periods. In Utah, dinosaurs from the Jurassic and the Cretaceous have been found and described.
Dinosaurs are divided into two major groups, the saurischian, or “lizard-hipped,” dinosaurs and the ornithichian, or “bird-hipped,” dinosaurs.
- The saurischian dinosaurs include the herbivorous (plant-eating), quadrupedal (four-footed) sauropods, and the carnivorous (meat-eating), bipedal (two-footed) theropods.
- The ornithichian dinosaurs are all herbivorous and are composed of many groups, including stegosaurs, ornithopods, and ceratopsians.
Fossils in Utah
A wide variety of fossils are found in Utah. Some of the most common fossils are of marine life like shells, fish, and trilobites. Land plant and animal fossils are also found in Utah and include dinosaurs, Ice Age animals, and leaves. Scroll through the timeline below to see Utah’s fossils and fossil environments from millions to hundreds of millions of years ago.
510 Million Years Ago
Approximately 510 million years ago (mya), during the Cambrian Period, trilobites thrived in the seas that covered western Utah. Trilobites are an extinct class of arthropods. Modern-day arthropods include insects, crabs, and spiders. These fossils can be found scattered across western Utah, particularly the House Range in Millard County.
340 Million Years Ago
Horn corals were abundant during the Mississippian (~340 mya). During this time, Utah was almost completely covered by a shallow sea. Horn corals are an extinct order of coral known as Rugosa. Abundant horn coral fossils can be found in the Confusion Range in Millard County.
215 Million Years Ago
During the Triassic Period (~215 mya), central Utah was a transition zone between river floodplains to the southeast and seas to the northwest. Abundant freshwater deposits yield the fossil remains of primitive fish.
200 Million Years Ago
Dinosaurs roamed through Utah during the Jurassic Period, leaving behind footprints in the soft sediments. At the beginning of the Jurassic (~200 mya), Utah was covered by a vast sand dune desert with inter-dune oases. Dinosaur tracks can be found in many areas, including the Moenave Formation at the St. George Dinosaur Discovery Site at Johnson Farm in Washington County.
170 Million Years Ago
During the Middle Jurassic (~170 mya) a shallow sea extended into Utah from the north and left many fossils, particularly the five-sided Isocrinus. Crinoids are still alive today in the seas of the world and are commonly known as sea lilies.
150 Million Years Ago
A broad coastal plain covered most of Utah during the Late Jurassic (~150 mya). Forests and lakes provided habitat for dinosaurs such as the Utah state fossil, Allosaurus, which dominated the land. Allosaurus was a meat-eating dinosaur that walked on two legs.
145 Million Years Ago
Petrified wood from the abundant forests that covered Utah during the Late Jurassic (~145 mya) can be found at Escalante Petrified Forest State Park in southern Utah.
90 Million Years Ago
During the Cretaceous (~90 mya), Utah was covered by river plains and coal-forming swamps and an interior seaway to the east. Coal (fossilized plant remains) is Utah’s most abundant fossil and can be found throughout central and eastern Utah. The fossilized remains of ammonites can be found in shales that were deposited in the seaway that covered eastern Utah during this time. Ammonites are an extinct group of cephalopods. Ammonites’ closest living relatives are the octopus, squid, cuttlefish, and nautilus.
50 Million Years Ago
Lush forests and a huge freshwater lake covered part of Utah during the early Tertiary (~50 mya). Plant fossils can be found throughout central and northern Utah in sedimentary rocks of this age.
2.6 Million Years Ago – 12,000 Years Ago
Several times during the Pleistocene Epoch (~2.6 mya – 12,000 ya), Utah was covered by glaciers. Ice Age mammals, such as the mammoth, roamed throughout Utah. The photo shows a mammoth tusk that was found near Fillmore, Utah, in Lake Bonneville deposits from about the time of the latest glacial episode about 15,000 years ago.
Utahraptor Megablock Fossil Project
Scott Madsen working on the megablock at the UGS.
The Utah Geological Survey (UGS) holds on behalf of the citizens of the State of Utah what is likely the most spectacular dinosaur fossil assemblage ever collected in the state. Recovered from the Stikes Quarry in southeastern Utah, the 9-ton block of sandstone contains thousands of bones of baby to adult Utahraptor dinosaurs, at least two iguanodont dinosaurs, and possibly other species. These animals became trapped in a quicksand-like mass likely while preying on one or more trapped plant-eating iguanodont dinosaurs. Many painstaking hours have been spent by expert preparators carefully exposing hundreds of bones from just a small portion of the accumulation of skeletons. The megablock is yielding numerous juvenile and adult skeletons that will be reassembled into a pack of Utahraptor dinosaurs and displayed at the Natural History Museum of Utah.
Learn about the 9-ton megablock of Utahraptor dinosaur fossils being prepared at the UGS.
Tracks & Other Trace Fossils
Trace fossils include evidence left by organisms but not the remains of body parts such as bones or shells. Examples of trace fossils include burrows, trails, scat, claw scratch marks, footprints, tail drags, and skin and body impressions. Tracks and other trace fossils can be good evidence for the size and identity of the animals that made them. Behaviors like eating habits, migration paths, and walking mechanics can also be inferred from some tracks if they are well preserved.
Tracks are formed and preserved by footprints left in mud, silt, or sand being filled in and buried. These layers of sediment later turn to stone with time and deeper burial. When subsequently exposed by erosion, often the prints themselves are not preserved but rather the infilled material is. Thus, many tracks are not found as impressions, but bumps (natural casts) on the underside of the stone layers that overlie the tracks.
In Utah, tracks can be found in many places such as the St. George Dinosaur Discovery Site at Johnson Farm and at Flaming Gorge Reservoir. Visit our interactive map to locate and visit some tracksites for yourself!
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