Paleontology is the study of the history of life on Earth as based on fossils. Fossils are the remains of plants, animals, fungi, bacteria, and single-celled living things that have been replaced by rock material or impressions of organisms preserved in rock.
Paleontologists use fossil remains to understand different aspects of extinct and living organisms. Individual fossils may contain information about an organism’s life and environment. Much like the rings of a tree, for example, each ring on the surface of an oyster shell denotes one year of its life. Studying oyster fossils can help paleontologists discover how long the oyster lived, and in what conditions. If the climate was favorable for the oyster, the oyster probably grew more quickly and the rings would be thicker. If the oyster struggled for survival, the rings would be thinner. Thinner rings would indicate an environment not favorable to organisms like the oyster—too warm or too cold, for example, or lacking nutrients necessary for them to grow.
Some fossils show how an organism lived. Amber, for instance, is hardened, fossilized tree resin. As the sticky resin dripped down a tree trunk, it trapped air bubbles, as well as small insects and some organisms as large as frogs and lizards. Paleontologists study amber, called “fossil resin,” to observe these complete specimens. Amber can preserve tissue as delicate as dragonfly wings. Some ants were trapped in amber while eating leaves, allowing scientists to know exactly what they ate, and how they ate it. Even the air bubbles trapped in amber are valuable to paleontologists. By analyzing the chemistry of the air, scientists can tell if there was a volcanic eruption or other atmospheric changes nearby.
The behavior of organisms can also be deduced from fossil evidence. Paleontologists suggest that hadrosaurs, duck-billed dinosaurs, lived in large herds, for instance. They made this hypothesis after observing evidence of social behavior, including a single site with approximately 10,000 skeletons.
Fossils can also provide evidence of the evolutionary history of organisms. Paleontologists infer that whales evolved from land-dwelling animals, for instance. Fossils of extinct animals closely related to whales have front limbs like paddles, similar to front legs. They even have tiny back limbs. Although the front limbs of these fossil animals are in some ways similar to legs, in other ways they also show strong similarities to the fins of modern whales.
Subdisciplines of Paleontology
The field of paleontology has many subdisciplines. A subdiscipline is a specialized field of study within a broader subject or discipline. In the case of paleontology, subdisciplines can focus on a specific fossil type or a specific aspect of the Earth, such as its climate.
One important subdiscipline is vertebrate paleontology, the study of fossils of animals with backbones. Vertebrate paleontologists have discovered and reconstructed the skeletons of dinosaurs, turtles, cats, and many other animals to show how they lived and their evolutionary history.
Using fossil evidence, vertebrate paleontologists deduced that pterosaurs, a group of flying reptiles, could fly by flapping their wings, as opposed to just gliding. Reconstructed skeletons of pterosaurs have hollow and light bones like modern birds.
One type of pterosaur, Quetzalcoatlus, is considered one of the largest flying creatures in history. It had a wingspan of 11 meters (36 feet). Paleontologists have competing theories about if and how Quetzalcoatlus flew. Some paleontologists argue it was too heavy to fly at all. Others maintain it could distribute its weight well enough to soar slowly. Still other scientists say Quetzalcoatlus was muscular enough to fly quickly over short distances. These theories demonstrate how vertebrate paleontologists can interpret fossil evidence differently.
Invertebrate paleontologists examine the fossils of animals without backbones—mollusks, corals, arthropods such as crabs and shrimp, echinoderms such as sand dollars and sea stars, sponges, and worms. Unlike vertebrates, invertebrates do not have bones—they do leave behind evidence of their existence in the form of fossilized shells and exoskeletons, impressions of their soft body parts, and tracks from their movement along the ground or ocean floor.
Invertebrate fossils are especially important to the study and reconstruction of prehistoric aquatic environments. For example, large communities of 200-million-year-old invertebrate marine fossils found in the deserts of the U.S. state of Nevada tell us that certain areas of the state were covered by water during that period of time.
Paleobotanists study the fossils of ancient plants. These fossils can be impressions of plants left on rock surfaces, or they can be parts of the plants themselves, such as leaves and seeds, that have been preserved by rock material. These fossils help us understand the evolution and diversity of plants, in addition to being a key part of the reconstruction of ancient environments and climates, subdisciplines known as paleoecology (the study of ancient environments) and paleoclimatology (the study of ancient climates).
At a small site in the Patagonia region of Argentina, paleobotanists discovered the fossils of more than 100 plant species that date back about 52 million years. Prior to this discovery, many scientists said South America’s biological diversity is a result of glaciers breaking up the continent into isolated ecosystem "islands" 2 million years ago. The Patagonia leaf fossils disprove this theory. Paleobotanists now have evidence that the continent’s diversity of plant species was present 50 million years before the end of the last ice age.
Some plant fossils are found in hard lumps called coal balls. Coal, a fossil fuel, is formed from the remains of decomposed plants. Coal balls are also formed from the plant remains of forests and swamps, but these materials did not turn into coal. They slowly petrified, or were replaced by rock. Coal balls, found in or near coal deposits, preserve evidence of the different plants that formed the coal, making them important for studying ancient environments, and for understanding a major energy source.
Micropaleontology is the study of fossils of microscopic organisms, such as protists, algae, tiny crustaceans, and pollen. Micropaleontologists use powerful electron microscopes to study microfossils that are generally smaller than four millimeters (0.16 inches). Microfossil species tend to be short-lived and abundant where they are found, which makes them helpful for identifying rock layers that are the same age, a process known as biostratigraphy. The chemical make-up of some microfossils can be used to learn about the environment when the organism was alive, making them important for paleoclimatology.
Micropaleontologists study shells from deep-sea microorganisms in order to understand how Earth’s climate has changed. Shells accumulate on the ocean floor after the organisms die. Because the organisms draw the elements for their shells from the ocean water around them, the composition of the shells reflects the current composition of the ocean. By chemically analyzing the shells, paleontologists can determine the amount of oxygen, carbon, and other life-sustaining nutrients in the ocean when the shells developed. They can then compare shells from one period of time to another, or from one geographic area to another. Differences in the chemical composition of the ocean can be good indicators of differences in climate.
Micropaleontologists often study the oldest fossils on Earth. The oldest fossils are of cyanobacteria, sometimes called blue-green algae or pond scum. Cyanobacteria grew in shallow oceans when the Earth was still cooling, billions of years ago. Fossils formed by cyanobacteria are called stromatolites. The oldest fossils on Earth are stromatolites discovered in western Australia that are 3.5 billion years old.
History of Paleontology
Throughout human history, fossils have been used, studied, and understood in different ways. Early civilizations used fossils for decorative or religious purposes, but did not always understand where they came from.
Although some ancient Greek and Roman scientists recognized that fossils were the remains of life forms, many early scholars believed fossils were evidence of mythological creatures such as dragons. From the Middle Ages until the early 1700s, fossils were widely regarded as works of the devil or of a higher power. Many people believed the remains had special curative or destructive powers. Many scholars also believed that fossils were remains left by Noah's flood and other biblical disasters.
Some ancient scientists did understand what fossils were, and were able to formulate complex hypotheses based on fossil evidence. Greek biologist Xenophanes discovered seashells on land, and deduced that the land was once a seafloor. Remarkably, Chinese scientist Shen Kuo was able to use fossilized bamboo to form a theory of climate change.
The formal science of paleontology—fossil collection and description—began in the 1700s, a period of time known as the Age of Enlightenment. Scientists began to describe and map rock formations and classify fossils. Geologists discovered that rock layers were the product of long periods of sediment buildup, rather than the result of single events or catastrophes. In the early 1800s, Georges Cuvier and William Smith, considered the pioneers of paleontology, found that rock layers in different areas could be compared and matched on the basis of their fossils.
Later that century, the works of Charles Lyell and Charles Darwin strongly influenced how society understood the history of Earth and its organisms. Lyell’s Principles of Geology stated that the fossils in one rock layer were similar, but fossils in other rock layers were different. This sequence could be used to show relationships between similar rock layers separated by great distances. Fossils discovered in South America may have more in common with fossils from Africa than fossils from different rock layers nearby.
Darwin’s On The Origin of Species observed somewhat similar sequencing in the living world. Darwin suggested that new species evolve over time. New fossil discoveries supported Darwin’s theory that creatures living in the distant past were different from, yet sometimes interconnected with, those living today. This theory allowed paleontologists to study living organisms for clues to understanding fossil evidence. The Archaeopteryx, for example, had wings like a bird, but had other features (such as teeth) typical of a type of dinosaur called a theropod. Now regarded as a very early bird, Archaeopteryx retains more similarities to theropods than does any modern bird. Studying the physical features of Archaeopteryx is an example of how paleontologists and other scientists establish a sequence, or ordering, of when one species evolved relative to another.
The dating of rock layers and fossils was revolutionized after the discovery of radioactivity in the late 1800s. Using a process known as radiometric dating, scientists can determine the age of a rock layer by examining how certain atoms in the rock have changed since the rock formed. As atoms change, they emit different levels of radioactivity. Changes in radioactivity are standard and can be accurately measured in units of time.
By measuring radioactive material in an ancient sample and comparing it to a current sample, scientists can calculate how much time has passed. Radiometric dating allows ages to be assigned to rock layers, which can then be used to determine the ages of fossils.
Paleontologists used radiometric dating to study the fossilized eggshells of Genyornis, an extinct bird from Australia. They discovered that Genyornis became extinct between 40,000 and 50,000 years ago. Fossil evidence from plants and other organisms in the region shows that there was abundant food for the large, flightless bird at the time of its extinction. Climate changes were too slow to explain the relatively quick extinction.
By studying human fossils and ancient Australian cave paintings that were dated to the same time period, paleontologists hypothesized that human beings—the earliest people to inhabit Australia—may have contributed to the extinction of Genyornis.
Modern paleontologists have a variety of tools that help them discover, examine, and describe fossils. Electron microscopes allow paleontologists to study the tiniest details of the smallest fossils. X-ray machines and CT scanners reveal fossils' internal structures. Advanced computer programs can analyze fossil data, reconstruct skeletons, and visualize the bodies and movements of extinct organisms.
Paleontologists and biologists used a CT scan to study the preserved body of a baby mammoth discovered in Siberia in 2007. A CT scanner rotates 360 degrees, allowing scientists to construct 3-D representations of the bones and tissue of the organism. Using this technology, scientists were able to see that the baby mammoth had healthy teeth, bones, and muscle tissue. However, the animal’s lungs and trunk were full of mud and debris. This suggested to scientists that the animal was healthy, but most likely suffocated in a muddy river or lake.
Scientists can even extract genetic material from bones and tissues.
Paleontologists made a remarkable genetic discovery when the bones of a Tyrannosaurus rex were broken during an excavation in the 1990s. Soft tissue was discovered inside the bones. Soft tissue is the actual connective tissue of an organism, such as muscles, fat, and blood. Soft tissue is rarely preserved during fossilization. Paleontologists usually must rely on fossilized remains—rocks. Paleontologists now hope to use this rare discovery of 68-million-year-old tissue to study the biology and possibly even the DNA of the T. rex.
Even with all these advancements, paleontologists still make important discoveries by using simple tools and basic techniques in the field.
The National Geographic Society supports field work in paleontology throughout the world. Emerging Explorer Zeresenay "Zeray" Alemseged conducts studies in northern Ethiopia. There, Alemseged and his colleagues unearth and study fossils that contribute to the understanding of human evolution.
Emerging Explorer Bolortsetseg Minjin is a paleontologist who has found fossils of dinosaurs, ancient mammals, and even corals in the Gobi Desert of Mongolia. She also works to teach Mongolian students about the dinosaurs in their own backyard, and is hoping to establish a paleontology museum in the country.
Many dig sites offer visitors the chance to watch paleontologists work in the field, including the Gray Fossil Site in Gray, Tennessee; the La Brea Tar Pits in Los Angeles, California; and the Ashfall Fossil Beds in Royal, Nebraska.
The 19th-century British fossil collector Mary Anning proved you don't have to be a paleontologist to contribute to science. Anning was one of the first people to collect, display, and correctly identify the fossils of ichthyosaurs, plesiosaurs, and pterosaurs. Her contributions to the understanding of Jurassic life were so impressive that in 2010, Anning was named among the ten British women who have most influenced the history of science.
Fossils and Myths
Ancient cultures did not always understand what fossils were, and adapted their discovery to fit with myths and stories.
China is rich in dinosaur fossils. Dinosaurs are ancient reptiles whose bones share characteristics with both reptiles and birds. Ancient Chinese people often interpreted dinosaur skeletons as the remains of flying dragons!
Fossilized remains of dwarf elephants have been found on several Mediterranean islands. Dwarf elephants grew to only 2 meters (6 feet) tall. Their skulls are about the same size as a human skull, with a large hole in the middle where the living animal's trunk is. In the ancient Mediterranean cultures of Greece and Rome, the remains of dwarf elephants were often interpreted as the remains of cyclopes, a type of feared, one-eyed giant.
Soaking Up History
The oldest fossils ever discovered are stromatolites, the remains of ancient cyanobacteria, or blue-green algae. The oldest animal fossils ever discovered are sponges. Prehistoric sponges have been discovered on the Arabian Peninsula and Australia.
Many paleontologists are also evolutionary biologists. Evolutionary biology is the study of the origin, development, and changes (evolution) in species over time. Other scientists that contribute to evolutionary biology are geologists and geneticists.
Term Part of Speech Definition Encyclopedic Entry abundant Adjective
in large amounts.
Age of Enlightenment Noun
(1700s) period in European history where science and reason were promoted as ideals of good citizens and society.
algae Plural Noun
(singular: alga) diverse group of aquatic organisms, the largest of which are seaweeds.
translucent, yellow-orange material made of the resin of ancient trees. Amber is sometimes considered a gemstone.
organisms that have a well-defined shape and limited growth, can move voluntarily, acquire food and digest it internally, and can respond rapidly to stimuli.
part of something that extends out from the main body, such as an arm or leg.
having to do with water.
extinct reptilian bird that lived about 150 million years ago.
invertebrate animal with a segmented body, exoskeleton, and jointed appendages.
view or interpretation.
atmospheric changes Noun
alterations in the layer of air surrounding the Earth, such as an increase of pollution or humidity.
the basic unit of an element, composed of three major parts: electrons, protons, and neutrons.
bacteria Plural Noun
(singular: bacterium) single-celled organisms found in every ecosystem on Earth.
having to do with the Bible, the holy book of Christianity.
scientist who studies living organisms.
study of the dating of rock layers.
disaster or sudden, violent change.
smallest working part of a living organism.
Charles Darwin Noun
(1809-1882) British naturalist.
Charles Lyell Noun
(1797-1875) English geologist.
study of the atoms and molecules that make up different substances.
complex way of life that developed as humans began to develop urban settlements.
Encyclopedic Entry: civilization classify Verb
to identify or arrange by specific type or characteristic.
all weather conditions for a given location over a period of time.
Encyclopedic Entry: climate climate change Noun
gradual changes in all the interconnected weather elements on our planet.
Encyclopedic Entry: climate change coal Noun
dark, solid fossil fuel mined from the earth.
coal ball Noun
spherical structure of fossilized plant matter found in and around coal deposits.
a coworker or partner.
connective tissue Noun
material that surrounds or links different organs or other parts of an organism.
one of the seven main land masses on Earth.
Encyclopedic Entry: continent coral Noun
tiny ocean animal, some of which secrete calcium carbonate to form reefs.
rocky outermost layer of Earth or other planet.
Encyclopedic Entry: crust crustacean Noun
type of animal (an arthropod) with a hard shell and segmented body that usually lives in the water.
CT scanner Noun
(computerized tomography scanner) device combining X-ray and computerized equipment to provide cross-sectional images of internal body structures. Also called a CAT scanner.
able to cure or treat a disease or illness.
type of aquatic bacteria that can photosynthesize light to create energy. Also called blue-green algae (even though it is not algae) and (in freshwater habitats) pond scum.
data Plural Noun
(singular: datum) information collected during a scientific study.
remains of something broken or destroyed; waste, or garbage.
to decay or break down.
to reach a conclusion based on clues or evidence.
area of land that receives no more than 25 centimeters (10 inches) of precipitation a year.
Encyclopedic Entry: desert dig site Noun
place where paleontologists, archaeologists, or other scientists are digging into the Earth to find artifacts or fossils. Also called an excavation.
to prove wrong.
(deoxyribonucleic acid) molecule in every living organism that contains specific genetic information on that organism.
phylum of marine invertebrate including sea stars and sea urchins.
community and interactions of living and nonliving things in an area.
Encyclopedic Entry: ecosystem electron microscope Noun
powerful device that uses electrons, not light, to magnify an image.
chemical that cannot be separated into simpler substances.
Emerging Explorer Noun
an adventurer, scientist, innovator, or storyteller recognized by National Geographic for their visionary work while still early in their careers.
to give off or send out.
conditions that surround and influence an organism or community.
to form or officially organize.
change in heritable traits of a population over time.
to develop new characteristics based on adaptation and natural selection.
area that has been dug up or exposed for study.
the hard external shell or covering of some animals.
no longer existing.
field work Noun
scientific studies done outside of a lab, classroom, or office.
Encyclopedic Entry: field work flipper Noun
large, flat limb used by marine mammals for swimming.
ecosystem filled with trees and underbrush.
to develop or create.
remnant, impression, or trace of an ancient organism.
Encyclopedic Entry: fossil fossil fuel Noun
coal, oil, or natural gas. Fossil fuels formed from the remains of ancient plants and animals.
fungi Plural Noun
(singular: fungus) organisms that survive by decomposing and absorbing nutrients in organic material such as soil or dead organisms.
having to do with genes, inherited characteristics or heredity.
extinct large, flightless bird indigenous to Australia.
person who studies the physical formations of the Earth.
Georges Cuvier Noun
(1769-1832) French paleontologist and biologist.
mass of ice that moves slowly over land.
Encyclopedic Entry: glacier Gobi Desert Noun
large desert in China and Mongolia.
group of animals.
statement or suggestion that explains certain questions about certain facts. A hypothesis is tested to determine if it is accurate.
ice age Noun
long period of cold climate where glaciers cover large parts of the Earth. The last ice age peaked about 20,000 years ago. Also called glacial age.
sign or signal.
animal without a spine.
invertebrate paleontology Noun
study of the fossils of animals without spines, such as corals, sponges, and insects.
to set one thing or organism apart from others.
organ in an animal that is necessary for breathing.
animal with hair that gives birth to live offspring. Female mammals produce milk to feed their offspring.
one of many extinct species of large animals related to elephants, with long, curved tusks. The last mammoths became extinct about 5,000 years ago.
having to do with the ocean.
fossil that can only be seen and analyzed with a microscope, such as a grain of pollen or a single bacterium.
very tiny living thing.
study of fossils of microorganisms.
Middle Ages Noun
(500-1500) period in European history between the Roman Empire and the Renaissance.
type of fungi that forms on the surface of materials.
large phylum of invertebrate animal, all possessing a mantle with a significant cavity used for breathing and excretion, a radula (except for bivalves), and the structure of the nervous system.
legend or traditional story.
National Geographic Society Noun
(1888) organization whose mission is "Inspiring people to care about the planet."
protected area built by birds to hatch their eggs and raise their young.
Noah's flood Noun
story in the Bible, a catastrophe that eliminated almost all life on Earth.
substance an organism needs for energy, growth, and life.
Encyclopedic Entry: nutrient oyster Noun
type of marine animal (mollusk).
study of the fossils of ancient plants.
study of the atmosphere of prehistoric Earth.
study of prehistoric environments and habitats.
person who studies fossils and life from early geologic periods.
the study of fossils and life from early geologic periods.
Encyclopedic Entry: paleontology Patagonia Noun
large plateau in southern South America, stretching from the Andes Mountains to the Atlantic Ocean.
to turn to stone.
person who is among the first to do something.
organism that produces its own food through photosynthesis and whose cells have walls.
powdery material produced by plants, each grain of which contains a male gamete capable of fertilizing a female ovule.
period of time that occurred before the invention of written records.
before or ahead of.
type of microscopic organism (not an animal, plant, or fungus).
extinct order of flying reptiles that flourished from 220 million-65 million years ago.
flying reptile that lived about 70 million years ago, native to North America.
having unstable atomic nuclei and emitting subatomic particles and radiation.
radiometric dating Noun
method of dating material such as rocks that compares the amount of a naturally occuring isotope of an atom and its decay rates. Also called radioactive dating.
clear, sticky substance produced by some plants.
to completely change a process or way of doing something.
part of a plant that secures it in the soil, obtains water and nutrients, and often stores food made by leaves.
surface layer of the bottom of the ocean.
solid material transported and deposited by water, ice, and wind.
Encyclopedic Entry: sediment sequence Verb
to put in order.
Shen Kuo Noun
(1031-1095) Chinese scientist, politician, and poet.
region of land stretching across Russia from the Ural Mountains to the Pacific Ocean.
bones of a body.
soft tissue Noun
connective tissue of an organism, such as blood, muscle, and skin.
individual organism that is a typical example of its classification.
simple type of marine animal permanently attached to something in the water.
fossil of ancient cyanobacteria that forms a rounded or column-like structure.
field of study within a larger area of research.
to be unable to breathe.
land permanently saturated with water and sometimes covered with it.
Encyclopedic Entry: swamp technology Noun
the science of using tools and complex machines to make human life easier or more profitable.
type of dinosaur that walked on two legs and was usually carnivorous.
T. rex Noun
(Tyrannosaurus rex) large carnivorous or scavenger dinosaur.
to dig up.
organism with a backbone or spine.
vertebrate paleontology Noun
study of the fossils of animals with spines, such as dinosaurs.
volcanic eruption Noun
activity that includes a discharge of gas, ash, or lava from a volcano.
William Smith Noun
(1769-1839) English geologist.
the distance between the tips of a bird's wings when stretched out.
animal with a long, limbless body.
(570-480 BCE) Greek philosopher and poet.