Encyclopedic Entry

Juvenile pterodactyls like this one are called "flaplings."

Photograph by Jonathan Blair

Microfossils
Even though most of us have only seen dinosaur fossils in museums, most fossils are not that big. Some of them are so small, you can't see them without a microscope.

Mary Anning
The 19th-century British fossil collector Mary Anning proved you don't have to be a paleontologist to contribute to science. Anning was the first person to collect, display, and correctly identify the fossils of dinosaurs such as 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 are the preserved remains, or traces of remains, of ancient organisms. Fossils are not the remains of the organism itself! They are rocks. 
 
A fossil can preserve an entire organism or just part of one. Bones, shells, feathers, and leaves can all become fossils. 
 
Fossils can be very large or very small. Microfossils are only visible with a microscope. Bacteria and pollen are microfossils. Macrofossils can be several meters long and weigh several tons. Macrofossils can be petrified trees or dinosaur bones.
 
Preserved remains become fossils if they reach an age of about 10,000 years. Fossils can come from the Archaeaean Eon (which began almost 4 billion years ago) all the way up to the Holocene Epoch (which continues today). The fossilized teeth of wooly mammoths are some of our most "recent" fossils. Some of the oldest fossils are those of ancient algae that lived in the ocean more than 3 billion years ago. 
 
Fossilization
 
The word fossil comes from the Latin word fossus, meaning "having been dug up." Fossils are often found in rock formations deep in the earth. 
 
Fossilization is the process of remains becoming fossils. Fossilization is rare. Most organisms decompose fairly quickly after they die. 
 
For an organism to be fossilized, the remains usually need to be covered by sediment soon after death. Sediment can include the sandy seafloor, lava, and even sticky tar.
 
Over time, minerals in the sediment seep into the remains. The remains become fossilized. Fossilization usually occur in organisms with hard, bony body parts, such as skeletons, teeth, or shells. Soft-bodied organisms, such as worms, are rarely fossilized. 
 
Sometimes, however, the sticky resin of a tree can become fossilized. This is called fossilized resin or amber. Amber can preserve the bodies of many delicate, soft-bodied organisms, such as ants, flies, and mosquitoes.
 
Body Fossils and Trace Fossils
 
The fossils of bones, teeth, and shells are called body fossils. Most dinosaur fossils are collections of body fossils. 
 
Trace fossils are rocks that have preserved evidence of biological activity. They are not fossilized remains, just the traces of organisms. The imprint of an ancient leaf or footprint is a trace fossil. Burrows can also create impressions in soft rocks or mud, leaving a trace fossil.
 
Paleontologists
 
Paleontologists are people who study fossils. Paleontologists find and study fossils all over the world, in almost every environment, from the hot desert to the humid jungle. Studying fossils helps them learn about when and how different species lived millions of years ago. Sometimes, fossils tell scientists how the Earth has changed.
 
Fossils of ancient marine animals called ammonites have been unearthed in the highest mountain range in the world, the Himalayas in Nepal. This tells scientists that millions of years ago, the rocks that became the Himalayas were at the bottom of the ocean.
 
Fossils of an ancient giant shark, a megalodon, have been found in the landlocked U.S. state of Utah. This tells scientists that millions of years ago, the middle of North America was probably entirely underwater.

Vocabulary

Term Part of Speech Definition Encyclopedic Entry

algae

Plural Noun

(singular: alga) diverse group of aquatic organisms, the largest of which are seaweeds.

amber

Noun

translucent, yellow-orange material made of the resin of ancient trees. Amber is sometimes considered a gemstone.

ancient

Adjective

very old.

bacteria

Plural Noun

(singular: bacterium) single-celled organisms found in every ecosystem on Earth.

body fossil

Noun

preserved evidence of what was once the body of an ancient organism, such as bones or teeth.

decompose

Verb

to decay or break down.

desert

Noun

area of land that receives no more than 25 centimeters (10 inches) of precipitation a year.

Encyclopedic Entry: desert

fossil

Noun

remnant, impression, or trace of an ancient organism.

Encyclopedic Entry: fossil

fossilize

Verb

to become a solid mineral.

humid

Adjective

air containing a large amount of water vapor.

jungle

Noun

tropical ecosystem filled with trees and underbrush.

Latin

Noun

language of ancient Rome and the Roman Empire.

lava

Noun

molten rock, or magma, that erupts from volcanoes or fissures in the Earth's surface.

macrofossil

Noun

fossil that is large enough to be seen and analyzed without a microscope.

mammoth

Noun

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.

megalodon

Noun

extinct shark that lived between 25 million and 1.5 million years ago.

microfossil

Noun

fossil that can only be seen and analyzed with a microscope, such as a grain of pollen or a single bacterium.

mineral

Noun

inorganic material that has a characteristic chemical composition and specific crystal structure.

organism

Noun

living or once-living thing.

paleontologist

Noun

person who studies fossils and life from early geologic periods.

pollen

Noun

powdery material produced by plants.

remains

Noun

materials left from a dead or absent organism.

resin

Noun

clear, sticky substance produced by some plants.

sediment

Noun

solid material transported and deposited by water, ice, and wind.

Encyclopedic Entry: sediment

seep

Verb

to slowly flow through a border.

shell

Noun

hard outer covering of an animal.

skeleton

Noun

bones of a body.

tar

Noun

dark, sticky petroleum product created from the decomposition of organic material such as wood.

trace fossil

Noun

preserved evidence of the presence or behavior of an ancient organism, such as tracks, feces, or burrows.

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Editor

Jeannie Evers

Producer

Caryl-Sue, National Geographic Society

Sources

Dunn, Margery G. (Editor). (1989, 1993). "Exploring Your World: The Adventure of Geography." Washington, D.C.: National Geographic Society.

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