Fossils are the remains of animals or plants from the past which have been preserved due to the physiochemical process known as fossilization
The process of fossilization
How do fossils form? How do they withstand thousands or millions of years without breaking down? When animal and plants die, there is still less than a one percent chance they will become fossils, even under the best geologic conditions. Natural decay, scavengers destruction by tectonic shifts and natural erosion are the most common reasons fossils don't form. However, if the conditions are just right, you can find organisms that are lucky enough to be preserved as fossils.
Mineralization is the most common form of fossilization with two main types, per-mineralization and replacement. Calcium carbonate, chitin, and silica can be replaced or filled in with a variety of minerals such as quartz, opal, or chalcedony during these processes.
Permineralization is when organisms are rapidly buried by sediment. The minerals in groundwater then fill in the organic spaces to create a natural cast.
Replacement fossilization also occurs when organic remains are rapidly buried. The organic materials, such as collagen in bones dissolve and are eventually completely replaced by minerals transported the groundwater.
The most common elements to be fossilized in replacement fossilization include the bones and teeth of vertebrates, mollusk shells, the exoskeletons of arthropods like crustaceans and trilobites, and the woody parts of plants. Calcium carbonate, chitin, and silica can be replaced or filled in with a variety of minerals such as quartz, opal, or chalcedony during this process.
It is possible to encounter fossils with preserved bodily tissue that is protected by surrounding material, called encasement fossils, but they are very rare. Mammoths frozen in Russian permafrost, insects preserved in amber or dire wolves preserved in asphalt at the La Brea Tar Pits in Los Angeles are all good examples of encasement fossils.
Trace fossils offer other important information about prehistoric life. These include casts and molds of dinosaur tracks, burrows made by worms and other animals, impressions of plants and leaves and any mark left in soft sediment by organisms that later turned into sedimentary rock. Amazingly, fossilized dung, called coprolites, has also been found.
Most fossils have been found in sedimentary rocks which are mostly formed from compressed layers of silt and clay near prehistoric waterways.
Natural erosion today can "weather out" and expose specimens at the surface or bury them further. Humans also bury or expose fossil remains through construction and road building.
For an interactive trip through geologic time, check out the Paleobiology Database Navigator to explore nearly 8,000 fossil discovery sites, with about 25,000 dinosaur fossils.
Where fossils are found
The first dinosaur ever to be described by scientists was found in Oxfordshire, England in the mid-18th century. The jawbone of Megalosaurus or "great lizard" that was found lived 186 million years ago during the Jurassic period. The British naturalist Sir Richard Owen coined the term "Dinosauria" in 1824.
Since then, dinosaurs have been found on every continent all over the world. The United States, Canada, China and Argentina boast some of the most prodigious numbers of species described.
The United States holds the honor of the greatest number of dinosaur species ever found, mostly throughout the deserts and badlands in Montana, Wyoming, Colorado, North Dakota, and South Dakota. One location in Alberta, Canada— Dinosaur Provincial Park—has documented 40 distinct species. Liaoning province in China lays claim to the well-preserved feathered fossils of the Sinosauropteryx, while Argentina is home to the largest sauropod dinosaurs some of which are the biggest terrestrial animals ever found, called the Titanosaur.
Collecting, cleaning and preparing fossils
Once fossils are found and deemed important enough to collect by paleontologists, their position, orientation and type are recorded. From there, the process of collecting and transporting them to a depository or larger institution begins.
In order to preserve the integrity of fossils, paleontologists use a variety of methods to retrieve them safely from the rock and dirt called "matrix" in which they're buried. Depending on the rock, tools such as pickaxes, rock hammers, chisels and even jackhammers may be used to further expose the fossil. Delicate handwork is then used to further uncover the specimen, making sure to leave the fossil encased in some matrix to protect it from cracking and breaking once it's exposed to air. To keep the fossil intact during transportation, special glues are applied to fill cracks and breaks. From there, each fossil is carefully encased in a plaster jacket for safe transport.
Cleaning & Preparing Fossils
It may come as a surprise that fossils do not come out of the ground the way they are displayed in museums. Once the fossil is transported to an accredited research institution, the process of preparing and fully exposing the specimen from the matrix begins.
Depending on the goals of the paleontologist, some fossils are collected and prepared with the goal of furthering paleontological research, while others are earmarked for public exhibition.
From there, specially trained fossil preparators work with a variety of mechanical, chemical and non-invasive tools to painstakingly uncover the delicate fossils we know and love.
Videos courtesy of Kelsie Abrams
The field of paleontology
"05528 Grand Canyon Paleontologists" by Grand Canyon NPS is licensed with CC BY 2.0.
The field of paleontology covers many different disciplines. These are some of the paleontologists you may meet on your discoveries:
Vertebrate Paleontology: the study of animals with spines such as dinosaurs, mammals, fish, amphibians, reptiles and birds.
Invertebrate Paleontology: the study of invertebrate animals such as snails, sea urchins
coral, crustaceans and insects.
Paleobotany: the study of fossil plants, algae.
Paleoanthropology: the study of fossilized bones and cultural artifacts of human ancestors such as early Homo sapiens, Neanderthals and Australopithecus afarensisalso like Lucy.
Ichnology: the study of fossil footprints and tracks.
Micropaleontology: the study of microscopic fossils such as bacteria, spores, pollen.
Taphonomy: the study of the history of deposition including the processes of decay, preservation and how fossils are formed.