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What is Paleontology?
Paleontology is the study of all ancient life. Not just prehistoric dinosaurs, but everything else too. That includes mammals, plants, fishes, insects, fungi, and even microbes! Paleontologists are like detectives. They examine the clues to solve mysteries about ancient organisms and environments.
1. Fossils are traces or remains of ancient life.
oviraptorid fossil
Fossils are evidence that life has existed on our planet for a really long time. Paleontologists study fossils to learn about the plants, animals, and microorganisms that lived thousands, millions, and even billions of years before humans.
praying mantis in amber
Most fossils form when organisms die and their remains are preserved in rocks. That happens when minerals replace the chemicals in the remains. But sometimes organisms freeze or dry out, forming mummies. And sometimes organisms like insects get stuck in tree sap. They are preserved when the sap turns into amber. Those are fossils too!
All fossils fall into two categories.
All fossils fall into two categories. Body fossils are formed from parts of the organism. These are usually hard parts like bones, teeth, shells, and eggs. Fossil plants count as body fossils too. Sometimes soft parts like feathers, and even chemicals, can be preserved too.
Archaeopteryx
This is a fossil of a small dinosaur named Archaeopteryx. The fossil has preserved delicate body parts like the dinosaur’s tiny teeth and thin, bony tail. It also shows clear imprints of the wings and feathers!
Do you see them?
amber with multiple insects
The delicate bodies of insects were preserved in amber. This fossilized tree resin acted like nature’s own bug trap!
How many insects do you see?
fossil leaf
These fossil leaves are from a plant that lived about 60 million years ago.
How many leaves do you see?
stromatolite
These rings are fossil stromatolites. They are structures built by tiny microbes called cyanobacteria over 1.5 billion years ago. The rings formed as the microbes grew in layers, trapping sand and minerals. Each fossil ring is like a snapshot of a day or season long ago!
How many sets of rings do you see?
Trace fossils are evidence of organisms’ behavior, rather than actual body parts. These include impressions of leaves and skin, nests, footprints, trackways, teeth marks, and coprolites (fossil poop!).
coprolite
This coprolite is fossilized poop. It turned into rock millions of years ago, so it’s no longer stinky or squishy!
Would you touch it?
trackway
These fossil footprints, called a trackway, were made by dinosaurs walking across muddy ground about 100 million years ago. They were discovered at Dinosaur Ridge, a fossil site in Colorado.
Can you tell which way the dinosaurs were walking? (Hint: The toes usually point in the direction a dinosaur was going!
fossilized skin
This fossil shows the bumpy, pebbly skin impressions of a saurischian (“lizard-hipped”) dinosaur.
What do you think the skin would have felt like when the dinosaur was alive?
Helminthoidichnites
These trails were made by tiny, wormlike animals called Helminthoidichnites as they moved through soft mud on the seafloor more than 500 million years ago. Their soft bodies usually decayed, so fossilized trails like these are often the only evidence they existed.
How many trails do you see?
2. Fossils form in rare conditions.
Most living things (99.99 percent) don’t become fossils. When organisms die, their bodies don’t usually stick around very long. Animals eat them. Decomposers like bacteria and fungi break them down. And what’s left over might get smashed up by waves, dissolve in water, or get weathered away.
Sometimes, though, dead organisms are preserved through a very rare process called fossilization.
When organisms die, they become buried in sediments like sand or mud. Traces of organisms, such as leaf impressions and footprints, can be buried too.
Over time, soft parts of organisms, like animal tissues and plant leaves, decompose. As more sediments build up, the remains become buried deeper underground.
Over millions of years, minerals from groundwater seep into hard parts of organisms, like bones, wood, and shells. Minerals slowly replace the materials and turn them into rock, forming fossils that keep the organism’s original shape.
fossil of a marine turtle that once lived in an ancient lagoon
3. Fossils have been found everywhere on Earth.
Check out this trilobite fossil a student found on a field trip to Death Valley National Park. You might find fossils in a stream, on a beach, or even in your own backyard!
Paleontologists have found fossils on every continent—even Antarctica! And not just on continents, either. There are fossils on the seafloor, too.
There are more fossils in some places than others. Dead organisms are more likely to fossilize in places like wetlands, river banks, and seafloors. There they can get covered by sediments that stay undisturbed and slowly turn into rock. That’s one reason so many fossils are shells.
By the time the remains and traces of organisms turn into rock, they are usually buried deep underground. But paleontologists don’t usually go mining for fossils. Instead, they go to areas where the fossils are already near the surface, or even exposed. That happens in places where there’s a lot of erosion, or where rock has slowly risen to form mountains.
Explore the map to see where Museum paleontologists hunt for fossils!
Morrison Rock Formation
Dinosaur, CO
Back in the Late Jurassic Period, about 150 million years ago, this area was just sand, great for forming fossils. Today, it is one of the richest and most important dinosaur fossil deposits in the world!
Why do you think this area has so many dinosaur fossils?
Nilpena Ediacara National Park
Flinders Ranges, South Australia
About 550 million years ago, this land wasn’t the dry Outback we see today. It was a shallow sea, where gentle waves moved sand to create ripples. In this ancient ocean, the very first animals lived. Some looked like sea creatures we see today. Others looked very strange and very different! Sometimes, storms buried the ancient organisms in the seabed, preserving a snapshot of the ancient seafloor. By studying the fossilized organisms and the rock around them, paleontologists can piece together what the ancient seafloor community was like long ago.
What do you think life was like in this ancient sea?
Anticosti Island
Québec
As waves from the ocean and rivers slowly wore away the island’s rocky cliffs, mudflats, and riverbanks, they revealed many fossils. Paleontologists have discovered fossils of many ancient sea animals that once lived there, like trilobites, crinoids, brachiopods, corals, sponges, and gastropods. These fossils and the surrounding rocks also contain important clues about what happened 445 million years ago. Many of these animals disappeared during a mass extinction event! But the evidence also shows that life slowly recovered afterward.
Can you picture life in this ancient sea?
Ralph’s Cave
Great Abaco Island, Bahamas
Bats have thrived in these caves for more than 10,000 years, since the end of the last Ice Age. But then the planet began to warm. That was hard on the bats. Next, humans arrived on the islands. They started making fires in caves and clearing plants to grow farms. That was hard on bats too. Some species became extinct, but others survived. Paleontologists have found fossils of both living and extinct bat species in the cave.
What do you think it would be like to explore a cave like this?
Djadochta Formation
Bayanzag, Bayn Dzak, Mongolia
Eighty million years ago, the climate here was extremely hot and extremely dry, just like today. It was a perfect spot for fossils to form. Paleontologists have even found fossil dinosaurs in postures that suggest they were buried alive in sand. The first known fossils of Protoceratops and Velociraptor were found here. So were the first confirmed dinosaur eggs.
Can you imagine the animals that lived here long ago?
4. Fossils help us understand the history of Earth.
Fossils are clues that help us figure out when ancient organisms lived. They also help us understand how long different species lived on Earth.
When paleontologists plan expeditions to hunt for fossils, they choose places with lots of sedimentary rock layers.
Fossils are typically found in sedimentary rock. These rocks formed from buried sediment, like sand, silt, dead plants, and animal remains. As the environment of the seafloor changed, the sediment moving through the water and settling on the bottom changed too. Over time, layers and layers of different kinds of sediment were laid down, one layer on top of another. Over millions of years, the layers became rock. And the plant and animal remains trapped within them became fossils.
Paleontologists study sedimentary rock layers to figure out the age of fossils found within them. They can determine the relative age of the fossils by looking at the order of rock layers. Layers closer to the bottom of a stack are usually older than those at the top. So fossils in lower rock layers are older than fossils in higher layers. Scientists can also determine the absolute age of fossils. Certain chemicals in rock layers break down slowly. Rock layers with more of these chemicals are younger. So the fossils found in them are younger too. Rock layers with less of these chemicals are older. That’s because the chemicals have broken down over time! So the fossils in those layers are older too. By combining relative and absolute dating, paleontologists can figure out the order of events and when they happened in Earth’s past.
ammonite
Paleontologists don’t just use rocks to determine the age of fossils. They also use fossils to determine the age of rocks! Some ancient organisms, like certain ammonites, spread around the world. But each of these organisms lived only during its own specific, short period of geologic time. Scientists call the fossils of these organisms index fossils. When they find index fossils in a rock layer, they can easily tell exactly when that layer formed. The layer dates to the short period when the organism lived.
Permian Period
299 to 251 million years ago
Dramatic changes in climate cause many amphibian species to become extinct. This allows sauropsids to thrive.
Cambrian Period
538 to 488.3 million years ago
A giant landmass called a “supercontinent” starts to break apart. The warm climate and wide, shallow seas help many new kinds of plants and animals grow in the ocean.
Quaternary Period
1.81 million years ago to present
During much of this time, large sheets of ice called glaciers cover some of the continents. Scientists call it the Ice Ages. Plants and animals that can adapt to the cold climate survive. Modern humans evolve.
Tertiary Period
65.5 to 1.81 million years ago
Grasslands spread over Earth, allowing grazing animals to thrive. Mammals come to dominate the land. The first ancient humans appear.
Jurassic Period
199.6 to 145.5 million years ago
Earth is dominated by huge dinosaurs such as the long-necked Diplodocus and Brachiosaurus. Birds, salamanders, snakes, and lizards evolve.
Cretaceous Period
145.5 to 65.5 million years ago
Dinosaur diversity reaches its peak. There is a wide range of species, like tyrannosaurs and horned, feathered, and duckbilled dinosaurs. By the end of the Cretaceous, all dinosaurs except birds disappear in a mass extinction event.
Triassic Period
251 to 199.6 million years ago
The first turtles, frogs, flying sauropsids, and small mammals appear. At the end of the Triassic Period, the climate was hot and dry. This provided the right conditions for the first dinosaurs to also evolve.
Carboniferous Period
359.2 to 299 million years ago
Warm, tropical conditions provide a favorable environment for insects and amphibians.
Devonian Period
416 to 359.2 million years ago
Plants become larger and spread over the land. The first trees, insects, and four-limbed land animals appear.
Silurian Period
443.7 to 416 million years ago
Rising sea levels and a warmer climate provide the right conditions for the first true land plants, primitive centipedes, and arachnids.
Ordovician Period
488.3 to 443.7 million years ago
Fish, coral, and shellfish evolve. Plants begin to appear on land. The continents continue to break apart and slowly move across the planet.
Precambrian Period
4,500 to 538 million years ago
At first, Earth is a hot, molten mass that is too harsh for life. Much later, single-celled forms of life evolve in the oceans. Over time, more complicated living things, such as jellyfish and worms, evolve.
Click on an organism
to explore this geologic timescale!
Precambrian Period
4,500 to 538 million years ago
At first, Earth is a hot, molten mass that is too harsh for life. Much later, single-celled forms of life evolve in the oceans. Over time, more complicated living things, such as jellyfish and worms, evolve.
Ordovician Period
488.3 to 443.7 million years ago
Fish, coral, and shellfish evolve. Plants begin to appear on land. The continents continue to break apart and slowly move across the planet.
Silurian Period
443.7 to 416 million years ago
Rising sea levels and a warmer climate provide the right conditions for the first true land plants, primitive centipedes, and arachnids.
Devonian Period
416 to 359.2 million years ago
Plants become larger and spread over the land. The first trees, insects, and four-limbed land animals appear.
Carboniferous Period
359.2 to 299 million years ago
Warm, tropical conditions provide a favorable environment for insects and amphibians.
Permian Period
299 to 251 million years ago
Dramatic changes in climate cause many amphibian species to become extinct. This allows sauropsids to thrive.
Triassic Period
251 to 199.6 million years ago
The first turtles, frogs, flying sauropsids, and small mammals appear. At the end of the Triassic Period, the climate was hot and dry. This provided the right conditions for the first dinosaurs to also evolve.
Cretaceous Period
145.5 to 65.5 million years ago
Dinosaur diversity reaches its peak. There is a wide range of species, like tyrannosaurs and horned, feathered, and duckbilled dinosaurs. By the end of the Cretaceous, all dinosaurs except birds disappear in a mass extinction event.
Jurassic Period
199.6 to 145.5 million years ago
Earth is dominated by huge dinosaurs such as the long-necked Diplodocus and Brachiosaurus. Birds, salamanders, snakes, and lizards evolve.
Tertiary Period
65.5 to 1.81 million years ago
Grasslands spread over Earth, allowing grazing animals to thrive. Mammals come to dominate the land. The first ancient humans appear.
Quaternary Period
1.81 million years ago to present
During much of this time, large sheets of ice called glaciers cover some of the continents. Scientists call it the Ice Ages. Plants and animals that can adapt to the cold climate survive. Modern humans evolve.
Cambrian Period
538 to 488.3 million years ago
A giant landmass called a “supercontinent” starts to break apart. The warm climate and wide, shallow seas help many new kinds of plants and animals grow in the ocean.
Click on an organism
to explore this geologic timescale!
5. Fossils are clues to ancient life and ancient environments.
Fossil seashells show the Himalaya Mountains were once an ocean!
Fossils can tell us a lot about how environments on Earth have changed over time. For example, the icy continent of Antarctica used to be so warm that a tropical forest grew there. We know because explorers discovered plant fossils there that are 200 to 250 million years old.
Paleontologists examine fossils to learn about individual organisms and species, too. For example, they can tell what an animal ate by looking at the shape of its teeth and jawbone. They also analyze coprolites, or fossilized poop. These often have fossils of undigested bones, seeds, or plant pieces in them. And paleontologists can study fossil footprints like dinosaur tracks to figure out how ancient animals moved. Together, all these clues can help paleontologists understand how ancient organisms lived. They help us understand how these organisms might have grown, hunted, built homes, got attention, or defended themselves.
Meganeura fossil
Meganeura was a gigantic ancient relative of the dragonfly. Its wingspan can be up to 2.5 feet (75 cm)! It lived about 300 mya, when Earth was much warmer. Paleontologists think it used the spines on its legs to hunt smaller insects.
Can you imagine insects being so big?
fossilized plant
The tiny round shapes on this fossilized plant are bite marks! Paleontologists study them to figure out what insect ate the leaves, how they ate, and what the environment was like long ago.
How many bite marks do you see?
T. rex skull
Tyrannosaurus rex was a ferocious predator with a powerful bite! Paleontologists can tell that from studying its sharp teeth and massive jawbone.
Can you imagine seeing a T. rex up close?
T. rex coprolite
Tyrannosaurs were carnivores. Paleontologists know that from studying fossilized poop. This coprolite specimen contains bones of another dinosaur that a T. rex ate!
What other clues do you think coprolites might contain?
trilobite
Trilobites were a group of extinct arthropods that lived in ancient oceans. Their exoskeleton was a hard outer shell made of separate pieces connected together. This armor protected their soft undersides from predators.
Did you know some trilobites could even roll up into balls to protect themselves?
foraminifera fossils
Paleontologists and paleogeologists can learn about climate by studying fossils like foraminifera. These tiny marine animals build their shells out of chemicals in seawater. The chemicals change with the water temperature. Scientists can tell how warm the ocean was at different times and places by analyzing the chemicals in fossil foraminifera shells.
Who knew that such tiny creatures can contain such important clues?
6. Fossils are clues to how life on Earth has changed over time.
Everything that ever lived on Earth is related to everything else. To figure out how ancient species are related, paleontologists study the fossil record. It is all the fossils scientists have discovered so far. It also includes the ages and locations of the rocks where the fossils were found.
When paleontologists study the fossil record, they compare fossils of different species. They look at how the physical traits of organisms are different and what they have in common. Shared traits are clues to how species are related to one another.
Paleontologists also combine clues from fossils and the rocks around them to build a history of life on Earth. For example, if they find a species in older rocks, they know that it lived earlier in Earth’s history. If paleontologists see a fossil in older rocks but not in newer ones, it means that species went extinct. Sometimes, paleontologists might observe a small change in an organism’s body and find it in rocks from different environments through time. This tells them the change may have helped the organism adapt to a new habitat. And over time, a new species might have evolved!
Based on fossil evidence, scientists can create diagrams called cladograms. Cladograms are a way to organize organisms by the physical traits they have in common. Like a family tree, a cladogram shows how species are related.
Cladogram of Dinosaurs and Their Relatives
This cladogram shows how animals are related. Animals that branch from the same dot, called a node, are more closely related. The branches on the right, coming from the “dinosaur” node, are all dinosaurs!
Do you spot any dinosaurs that are still alive today?
7. Fossils can’t tell us everything about ancient life.
Most of what fossilizes are hard parts like bones and shells. Squishy stuff like organs and soft tissues don’t usually last. Neither does DNA. Because extinct animals are (by definition) dead, we can’t watch them to see how they behave. That means there’s a lot we can’t learn about ancient life from fossils.
Fortunately, scientists have other ways to learn about extinct organisms. They can observe their living relatives to figure out how ancient organisms developed, moved, and behaved. What else will we discover in the future?
Take a look at how our understanding of Tyrannosaurus rex has changed over time.
A century ago, people thought T. rex was a giant lizard with scaly skin. They thought it stood upright like a kangaroo, dragging its tail and moving very slowly. Based on new fossil discoveries, scientists now think T. rex may have had simple feathers, especially when it was young. Scientists also use computers to model how this dinosaur’s muscles and bones worked. They now think T. rex stood with its body almost parallel to the ground. Its long tail stayed up in the air to balance its big head. This posture helped this predator run fast and hunt prey!
8. Studying ancient life helps us understand life and environments today.
Understanding the past is a way to protect the future. We can learn from studying the fossil record of mass extinctions in the past. One lesson is that when change happens quickly, many species don’t have the right adaptations to survive, so they become extinct.
In the billions of years since life first appeared on Earth, the climate has gone through many changes. Right now, human activities, such as burning fossil fuels, are leading to major changes around the world. They are happening much more quickly than anything observed before in the fossil record. And evidence from Earth’s past suggests that if these changes keep happening so quickly, many species may become extinct. It’s hard to predict exactly what will happen. But humans also have the power to make choices that protect our planet and help life thrive.
Scientists added bright colors to this enlarged photo to make the super tiny foraminifera microfossils easier to see. They are usually just 0.05 to 1 mm in size. That’s even smaller than a period at the end of a sentence! By studying the chemical makeup of these microfossils, scientists can learn how much carbon dioxide was in ancient oceans and how warm the water was. Comparing this to today’s ocean conditions helps scientists track how Earth’s climate has changed over time.
Image Credits:
illustrations, Zack Faust ©AMNH; fossil in ground, © AMNH; amber, © AMNH; amber w/ insects, J. Beckett/© AMNH; Archaeopteryx, © AMNH; fossil leaf, Tyrex Paleobotany/CC BY-SA 4.0; stromatolite, Scott Evans/© AMNH; coprolite, University of Arizona Mineral Museum; Helminthoidichnites, Scott Evans/© AMNH; skin impression, Denis Finnin/© AMNH; trackways, Devin D’Agostino/© AMNH; fossilization process, Illustrations by Zack Faust/© AMNH; adapted from art by UC Museum of Paleontology/CC BY-NC-SA 4.0; turtle fossil, Siepmann/AGE Fotostock; kid with fossil, Scott Evans/© AMNH; Anticosti Island, Melanie Hopkins/© AMNH; Djadochta Formation, Amanderson/CC BY 2.0; Morrison Rock Formation, Mark Ryan/CC BY-NC-ND 2.0; Nilpena excavation, Scott Evans/© AMNH; Ralph's Cave, Melanie Hopkins/© AMNH; fossils in trays, Alvaro Keding/© AMNH; clear sedimentary rock layers, Kirsh/CC BY-SA 2.0; ammonite, Alvaro Keding/© AMNH; Himalayas, A. Ostrovsky/CC BY-SA 2.0; foraminifera fossils, Siim Sepp/CC BY-SA 3.0; fossil leaf, Denver Museum of Nature & Science; Meganeura fossil, Tylwyth Eldar/CC BY-SA 4.0; T. rex coprolite, public domain by Karen Chin / USGS; T. rex skull, Craig Chesek/© AMNH; trilobite, © AMNH; paleontologist in lab, © AMNH; vintage T. rex illustration, Charles R. Knight; modern T.rex illustration, Zhao Chuang/PNSO; Foraminifera microfossils, Steve Gschmeissner/Science Source.