POPULAR GEOLOGY

Dinosaurs & Fossils

Utah contains one of the most complete fossil records on Earth. This record spans almost 2 billion years! Some of the most common fossils are of early marine life such as mollusks (snails, clams, and ammonites), fish, and trilobites from Paleozoic-age rocks in Utah’s West Desert. Eastern Utah contains younger, Mesozoic- and Cenozoic-age rocks that were deposited as layers of marine and terrestrial (land) sediments in Jurassic- and Cretaceous-age inland seas and terrestrial environments. The preserved fossils from the Mesozoic and Cenozoic include an amazing variety of plants and animals: from insects, freshwater clams, mammals, and dinosaurs in the terrestrial rocks, to mollusks, fish, and marine reptiles in the marine rocks.

Utah is famous for its dinosaur fossils and related discoveries, behind only China in regard to the number of dinosaur types found. Utah’s Cenozoic rocks were deposited after the extinction of the non-avian (non-bird) dinosaurs. These rocks document the origins of many modern mammal groups. Utah also contains abundant fossils from the Pleistocene which include extinct bison, camels, giant ground sloths, horses, musk-oxen, mammoths, and mastodons.

Scroll through the timeline below to see a selection of Utah’s fossils and fossil environments from millions to hundreds of millions of years ago.

Trilobite fossils and a map of Utah that is half-covered by water. A star indicates the fossil was found in western Utah.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.

510 MILLION YEARS AGO

Trilobite fossils and a map of Utah that is half-covered by water. A star indicates the fossil was found in western Utah.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.

Horn-shaped fossils and a map of Utah that is mostly covered by water. A star indicates the fossil was found in western Utah.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.

340 MILLION YEARS AGO

Horn-shaped fossils and a map of Utah that is mostly covered by water. A star indicates the fossil was found in western Utah.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.

Fish fossil next to a map of Utah that is mostly land. A star indicated the fossil was found in eastern Utah.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.

215 MILLION YEARS AGO

Fish fossil next to a map of Utah that is mostly land. A star indicated the fossil was found in eastern Utah.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.

A dinosaur footprint and a map of Utah with only land. A star indicates the fossil was found in southern Utah.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.

200 MILLION YEARS AGO

A dinosaur footprint and a map of Utah with only land. A star indicates the fossil was found in southern Utah.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.

Small, star-shaped fossils and a map of Utah with land and water. A star indicates the fossils were found in southern Utah.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.

170 MILLION YEARS AGO

Small, star-shaped fossils and a map of Utah with land and water. A star indicates the fossils were found in southern Utah.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.

A dinosaur skeleton and a map of Utah with land and rivers. A star indicates the fossil was found in central Utah.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.

150 MILLION YEARS AGO

A dinosaur skeleton and a map of Utah with land and rivers. A star indicates the fossil was found in central Utah.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.

A large piece of petrified wood and a map of Utah with land and rivers. A star indicates the wood was found in southern Utah.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.

145 MILLION YEARS AGO

A large piece of petrified wood and a map of Utah with land and rivers. A star indicates the wood was found in southern Utah.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.

A spiraled shell fossil and a map of Utah with water to the east. A star indicates the fossil was found in eastern Utah90 MILLION YEARS AGO

During the Cretaceous (~90 mya), Utah was covered by river plains and coal-forming swamps and an inland sea 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.

90 MILLION YEARS AGO

A spiraled shell fossil and a map of Utah with water to the east. A star indicates the fossil was found in eastern UtahDuring the Cretaceous (~90 mya), Utah was covered by river plains and coal-forming swamps and an inland sea 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.

A fossil leaf imprint on a rock and a map of Utah with vegetation covering most of the state. A star indicates the fossil was found in eastern Utah.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.

50 MILLION YEARS AGO

A fossil leaf imprint on a rock and a map of Utah with vegetation covering most of the state. A star indicates the fossil was found in eastern Utah.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.

A fossil mammoth tusk and map of Utah with Lake Bonneville. A star indicates the fossil was found in western Utah.2.6 MILLION YEARS AGO to 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.

2.6 MILLION YEARS AGO to 12,000 YEARS AGO

A fossil mammoth tusk and map of Utah with Lake Bonneville. A star indicates the fossil was found in western Utah.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.

Why Does Utah Have So Many Fossils?

The simple answer is: we have the rocks! To become a fossil, an animal has to die and be buried in sediments that will preserve some part of its body. The hard parts, such as the shell or bone of an animal, are those that are most commonly preserved. Then those sediments have to be buried and, in most cases, turned to rock. These rocks then need to be exposed so that the fossil can be found.

The rocks of Utah’s West Desert are primarily marine rocks that were deposited when Utah was near the margin of the ocean (Nevada and California were not there yet). During that time, tens of thousands of feet of rock were deposited along with the fossils they contain. Later uplift and erosion of these rocks has exposed them so that we can find the fossils preserved within them. The Mesozoic rocks in eastern Utah were deposited in shallow seas and on adjoining land, but were ultimately also uplifted and eroded to be exposed. The animals and plants of the Mesozoic lived on land that was slowly subsiding (sinking). The subsidence drove fossil preservation because when some of the plants and animals died and were buried, the sediments that enclosed them were preserved. Several vertical miles of Mesozoic rock record this time period and form the spectacular red rock scenery of eastern Utah and its national parks such as Arches and Zion. Deposition and later erosion of these rocks make Utah a treasure trove of fossils.

Click here to go to the Visitor Information Guide to Fossils in Utah.
Click here to go to the Visitor Information Guide to Fossils in Utah.
Rock, Mineral, and Fossil Collecting Rules and Regulations
What Should You Do if You Find a Fossil? Keep or Report?

Utah Dinosaurs

When many people think of dinosaurs, what comes to mind are large animals like Tyrannosaurus and Triceratops that lived during the Mesozoic Era, the so-called “Age of Dinosaurs.” The majority of dinosaur paleontologists now agree that birds evolved from a group of theropods (meat-eating dinosaurs). Therefore, not all dinosaurs went extinct at the end of the Cretaceous Period, 66 million years ago, only what we call the non-avian dinosaurs. The avian dinosaurs (birds) are still here and are the most diverse and abundant group of vertebrates on land. In that respect, we are still living in the “Age of Dinosaurs”!

Dinosaur paleontology is a very active area of scientific research, and every year over 20 scientific papers are published on dinosaur fossils in Utah. The amount of information that we have about the biology of dinosaurs increases every day. Dinosaur fossils from Utah play a large role in much of this new information, and over the past 30 years we have gone from a relatively small number of dinosaur species known from just a few geological formations, to well over 100 species from numerous formations. Researchers from all over the United States and the world come to Utah to excavate and study dinosaurs and other fossils. Over half of the permits in the country issued by the Bureau of Land Management to conduct paleontological research on the lands they manage are for Utah.

Utah In The Age of Dinosaurs

Explore different species of Utah dinosaurs and details about their environments!

Click here to go to the Utahraptor Megablock Fossil Project page.
Click here to go to the Utahraptor Megablock Fossil Project page.
Search
TitleTopicYear
Fossil Mountain, Millard County, Utah Landforms, Fossils 2023
The Utah Geological Survey and the National Park Service Dinosaurs and Fossils 2023
Paleo News: New Discoveries of Morrison Formation Plant Fossils Expand Our Knowledge of Jurassic Ecosystems Plant Fossils 2022
Needing a Great Resource for Teaching Your Students About Utah Fossils? Technology 2020
Utah’s Early Cretaceous Fossils Provide Critical Data on the Opening of the Atlantic Ocean Dinosaurs 2018
Mysteries of the Uinta Mountains – Commonly Asked Questions Mountains 2018
Parowan Gap, Iron County Landforms 2018
Does Utah Preserve North America’s Oldest Cretaceous Dinosaurs Because of Ancient Salt Deposits? Dinosaurs 2017
Wolverine Petrified Forest, Garfield County Fossils 2017
UGS Paleontologists Collect Dinosaur Megablock Dinosaurs 2015
St. George Dinosaur Discovery Site at Johnson’s Farm, Washington County Tracks 2014
When sharks, rays & sawfish ruled Utah’s rivers Fossils 2014
Spectacular pterosaur track slab begins its cross-country journey Tracks 2013
The Thumb-Spiked Iguanodontians – Dinosaurian Cows of the Early Cretaceous Dinosaurs 2013
UGS Scientist Honored in Naming of Utah’s Newest Dinosaur: Martharaptor greenriverensis Dinosaurs 2013
Are those animal tracks in the sidewalk? Tracks 2012
Utah’s Prehistoric Tanks: The Ankylosaurs Dinosaurs 2011
Utah’s Glacial Geology Glaciers 2010
Glacial Landforms in Big and Little Cottonwood Canyons Glaciers 2010
Ice Ages – What are they and what causes them? Ice Age 2010
The fossil preparation lab at the Utah Geological Survey: Bringing Earth’s ancient past to life Fossils 2010
Utah’s Pleistocene Fossils: Keys for Assessing Climate and Environmental Change Ice Age 2010
Scientific Investigations at Hanksville-Burpee Dinosaur Quarry Dinosaurs 2009
What should you do if you find a fossil? Can you keep it? Should you report it? Fossils 2009
G.K. Gilbert Geologic View Park, Salt Lake County Landforms 2008
Glacial striations and slickensides – What are those groovy rocks and how did they get that way? Glaciers 2008
Fossil environments in Utah (pdf) Fossils 2008
New Horned Dinosaurs from the Wahweap Formation Dinosaurs 2007
The Case for Fishing Dinosaurs Tracks 2007
New Discoveries of Fossil Mammals Fossils 2006
Utah’s Newly Recognized Dinosaur Record Dinosaurs 2005
Dinosaur Record from the Early Cretaceous Cedar Mountain Formation Dinosaurs 2005
Utah’s oldest fossils are found in the Uinta Mountains Fossils 2005
Inventory and Management of Utah's Fossil Resources Fossils 2005
Falcarius utahensis; Killer Dinos Turned Vegetarian Dinosaurs 2005
Are there glaciers in Utah’s mountains? Glaciers 2003
The Wolverine Petrified Forest Fossils 2003
Rules and Regulations Regarding Rock, Mineral, and Fossil Collecting in Utah Rocks and Minerals 2003
Discovery of a New Pterosaur Tracksite at Flaming Gorge Reservoir Tracks 2002
Pahvant Butte in the Black Rock Desert Volcanoes 2002
St. George Dinosaur Tracksite Tracks 2002
Trilobites and the Cambrian Environment of Utah Fossils 1996
Utah’s Wildlife in the Ice Age Ice Age 1996
Special Issue on Utah Minerals, Fossils, Geology Rocks and Minerals 1994
The geologic story of GK Gilbert Geologic View Park Geologic History
St. George Dinosaur Tracksite (pdf) Tracks
Squatting Dinosaur Tracks Tracks
Mammoth tusk discovery adds to our knowledge of life along the shores of Lake Bonneville Ice Age
Dinosaurs Making Tracks at Flaming Gorge Reservoir Tracks

Dinosaurs and Fossils Articles: 49