Prehistoric Animals


Welcome to ! We are the world's largest online educational resource dedicated to dinosaurs, paleontology, prehistoric animals and everything related to it.

Insect fossil in amber

Digging for Dinosaurs - The Science of Fossil Hunting

The formation of fossils

Fossils are the key clues on which the difficult but fascinating work of the paleontologist detective is based. Fossils are like notes written in stone. Any living thing may have left traces, but some organisms lend themselves better to fossilization than others. Usually only the hard parts of a plant or animal become fossilized, which is rarely the case for muscles, skin and internal organs. Shellfish shells, for example, and vertebrate bones are more likely to be preserved than jellyfish and worm bodies. The fossil remains of these are in fact almost nonexistent. Footprints, eggs and feces can also be fossilized.


Fossilization can occur in many ways but generally involves an environment with water and the burial of organism remains in the sediments of a stream, lake or ocean. Once the soft parts are putrefied, the bones or shells are enshrined in mud and silt. Over time, the sediments are transformed into rock and the remains trapped create an imprint of their original shape. Sometimes the remains of organisms are completely replaced, cell by cell, by minerals under the action of groundwater in the surrounding rock. This is called petrification. In other cases, the bone dissolves leaving a cavity in the rock - a natural mold that can be filled with minerals. Another form of fossilization more unusual: insects and small animals that get stuck in the resin of a tree, which after hardened will turn into amber, a semi-precious stone where they will be perfectly preserved. It also happens that the imprints left in the rock are filled with silica and that the fossilized shell or skeleton takes the iridescent reflections of the opal. When, relatively rarely, an animal is caught in the burning ashes of a volcano, the fossil is reduced to a cavity having its exact shape. By far the most numerous fossils are those of crustaceans living in shallow water. Corals, clams, snails and other invertebrates make up the bulk of the collections. Plants, too, can become fossilized, but this is more rare. Coal, for example, is nothing more than a fossil fuel from whole forests, but plants almost never retain their original structure because they are compressed up to 1 / 100th of their original thickness.

Land animals

The remains of terrestrial animals are fossilized even more rarely than those of plants. To be able to fossilize, these animals must be dead near or in a watercourse, then covered with mud and silt. The fact that all the dinosaurs lived, a priori, on the mainland explains the low number of vestiges they left. It is therefore likely that we will never know all the dinosaurs that have existed. Animals that roamed the river plains or estuaries left traces of their passage in the form of footprints. Herd tracks are sometimes kept the same way. Sometimes, whole colonies have been flooded and are now fossilized.

Fossil dating

It is very important to be able to date the rocks and the fossils that one discovers there. Scientists have come up with a number of ways to do this. There are several methods for dating rocks. One of these, radiometric dating, measures the degree of disintegration of various isotopes (that is, the different forms of a chemical element) contained in particular minerals in the rock. Another technique, paleomagnetic dating, measures the ancient magnetism of a rock. A third, the dating of fission traces, consists in observing the effects of the decomposition of uranium in zircon crystals.

Radiometric dating

One method is to measure the degree of disintegration of the isotope of potassium 40 which is converted into a gas called argon 40. Potassium is a common element of minerals such as feldspars, which are often found in basalt and other effusive rocks. A small proportion of naturally occurring potassium contains potassium 40, which decays at a steady rate and is known to produce argon 40. When a rock is melting, the argon it contains can then escape and the clock is thus raised. Once the rock is solidified, the argon caught in its trap begins to form again. The older the solidification, the greater the amount of gas thus accumulated. By measuring the amount of argon 40 relative to the amount of potassium 40, the exact time that has elapsed since the molten rock has solidified is known exactly. Basalts formed from lava are widespread. Over time, these eruptive rocks formed alternating layers with sedimentary rocks. By dating the potassium and argon they contain, it is therefore possible to determine the age of sedimentary rock layers above and below. Potassium / argon dates are not the only ones used in radiochronology. There are also rubidium / strontium, uranium / lead and samarium / neodymium pairs, but the technique is identical: by measuring the degree of disintegration of these isotopes, it is precisely possible to evaluate when the process was going up. Isotope pairs that disintegrate at different rates are useful for dating over different periods. One of the best-known techniques is that of carbon 14 dating. A living organism uses carbon-14 as well as the carbon of the atmosphere. The day it dies, the exchanges with his environment cease and the carbon 14 it contains begins to disintegrate. As with other radiometric methods, to date carbon 14 it is necessary to determine the value of the isotope that remains in the body. But carbon 14 disintegrates fast enough that it only allows dating less than 50 000 years old and therefore does not serve fossils.

Palaeomagnetic dating

For reasons that are not entirely clear, it happens that the magnetic north of the Earth is to the south and vice versa. These different polarities are recorded in eruptive rocks that have cooled like basalt. The tiny magnetic particles contained in the lava orient themselves in the dominant terrestrial field and keep their initial orientation even when the lava solidifies. The history of these changes of polarity, of different durations, is engraved in the ocean floor. When the study of the magnetic orientation of the terrestrial basalts makes it possible to establish a correspondence with the story told by the seabed, one can then determine the age of these basalts and surrounding rocks.

Dating of fission traces

Zircon naturally contains uranium. One of the unstable isotopes of uranium, U 238, is subject to the fission phenomenon, a nuclear reaction in which it splits to form a more stable isotope. When this occurs inside a zircon crystal, the separation is so violent that it causes tiny scratches in the crystalline matrix. As with any other disintegration, that of U 238 is at a known rate, so that the older the zircon, the greater the number of detectable streaks or fission marks. The dating will then consist essentially of counting the number of scratches in the zircon crystals.

Fossil search

When we know what we are looking for and to whom we must ask, it only takes a minimum of steps to obtain the best results. Major museums with collections of dinosaur fossils employ at least one specialist in vertebrate paleontology. Much of their work involves discovering, studying and presenting new specimens. The amateur researchers, on the other hand, will make it easier for them by doing some preliminary research to find suitable places because we know that only certain types of rock can contain dinosaur fossils.


Museums are a good starting point, as they almost always indicate where their fossils come from. You will then be able to visit the site that has been indicated to you - if a fossil has already been found there, there may be others waiting for you. The rock erodes a little more each season and a specimen that remained hidden until then, will one day or another be exposed. If the remains in question have been discovered long ago, you will likely find others there, as the erosion has done its work. Some types of rocks or formations tend to be more productive. After having located those from which the existing specimens come, you can consult a geological map to find the same type of rock elsewhere. Also locate small streams and places where the road cuts a mountain.

On the spot

Look for places where the rock is exposed, such as rocky deserts, dry stream beds, cliffs, roads cut through a massif and quarries. Bone fragments often break off from a fossil recently exposed by the action of water and are carried downstream by wind or rain. Walk up the slope or stream to see where they come from. The museums that are most successful at renewing their collections are those working in collaboration with amateur researchers and local landowners. Many of these hobbyists are very knowledgeable and the owners who know their terrain in great detail are best placed to find the open fossils found there. Some museums are setting up specious programs for fossil researchers, and are working to inform landowners about what to look for. If you think you've found a dinosaur fossil, refrain from digging, and if you've picked up a bone that looks like a fossil, examine it carefully and put it back exactly where you found it. Examine the area, without turning anything upside down unnecessarily. Once the excavations are completed, take your findings to a museum for identification; and be sure to note the exact location of the discovery. Also note your landmarks so you can return.


At the scene of searches as well as at the scene of a crime, it is necessary to work with minutia to find all the clues. When a dinosaur fossil has been found, it must be exhumed as soon as possible, because even if it has been buried for hundreds of millions of years it is likely to deteriorate quickly as soon as it is exposed to the elements. But this operation must be done with great care. Unlike excavations that can be undertaken by a small group or even a single person, exhumation requires significant equipment and a great deal of manpower. The organization of such a team alone can require considerable work.

Find the complete fossil

When a fragment of fossil has been discovered, the remaining part must be found as soon as possible, whether it is nearby or has been taken to a ravine. If the fossil has just been exposed and if it has not been carried away by rain or wind, it is likely that the remaining part will not be very far, and the surrounding rock should be carefully cleaned with a brush or a chisel. During this time, a person with a good view can rake the surroundings, and even beyond, to look for other fragments that could have been washed away by the wind or the rain.


When you are sure that the dinosaur fossil is complete, bone surveys and labeling must be done. The information gathered from the position in which each bone was found can be as important as its exhumation. No bone shall be moved until its position and orientation have been recorded on a grid plan and until it has been numbered. The site is generally delimited by a line and cards. Each square meter is then covered with a wooden frame of the same size supporting a wire mesh of 10 cm section. A record of the bones within each square decimeter is made on grid paper, and each portion of the wire is photographed.


To accurately report searches, you must photograph the bones in their original environment before extracting them - the best for that being the combination of still images and video images. An annotated sketch can also be used. The next step is to label the bones. Sticky labels are likely to peel off and get lost, better use an indelible marker. If you think a bone needs to be consolidated with a special glue, apply it before labeling as it may spread the marker ink.


Once the surveys, photos and tagging are complete, you can proceed with the extraction of the fossil using a method that will vary according to the nature of the fossil and the rock where it is located. If it is in sand or earth, simply lift it carefully and put it in its packaging. Very small vestiges such as bone fragments or teeth can be wrapped in paper towels and stored temporarily in a small box. Larger fossils should be wrapped in a piece of cloth or burlap before being surrounded by straw and placed in a crate. If the fossil is in a compact rock, or even hard clay, you can use a chisel to cut the rock or clear small blocks by inserting the blade into the existing cracks. You will then need different tools depending on the hardness of the rock: pickaxe, saw, chisel, dental drill driven by a small electric motor with a flexible penknife. Be careful not to break a bone by using a hammer with a little too much energy.


When you are about to clear your block of rock, be sure to protect the part of the fossil that is flush, as well as the other sides of the block if necessary. If the rock and fossil are strong enough, just wrap it in a good layer of wet newsprint; otherwise, layers of paper towels, newspaper and canvas should be layered before plaster is applied to consolidate the remains during all transport operations. This technique is effective, but sometimes long and painful. After all this work, you will probably be very happy to give a last stroke of mass to clear the block of rock. Cover the last side of it and apply a layer of plaster as needed, as you did on other faces. Once tagged, your fossil will finally be ready to go to the nearest museum where it will be examined and, who knows, may be exposed in a showcase.

Harvest and transport of fossils

New discoveries by fossil researchers are fundamental to the health of today's dinosaur palaeontology. The first problem facing any fossil scientist is to know where he should begin his excavations. Not all sites contain dinosaur fossils or any other kind. Paleontologists spend a lot of time studying geological maps that will tell them where the rocks of interest are likely to be exposed. Requests to administrations for permission to conduct investigations and the necessary funds will take even longer. They must also prepare their expedition and decide on the equipment and material to take away: tools, food, water and fuel.

On the spot

We often talk about the "digs" of paleontologists who are looking for dinosaurs, but that is not quite right, even if they are part of their job. Once they have found the rocks that interest them, paleontologists spend most of their days with their backs bowed and their eyes fixed on the rock. They rarely take a shovel to dig the earth. They leave erosion on the hillside to bare the bones. Most of the time, they survey valleys and detritic areas in search of bone fragments from overhanging hills. When they find a bone, the fragments they will see on the hillside will allow them to go back to the source. Each fossil discovered is precisely located on the map. The new GPS system (Geographic Positioning System) made it much easier for them. Then comes the time to decide the procedure. If they are small bones (less than 5 cm), they will simply roll them in paper towels; the largest fossils must be put in special packaging. The transport of large fossils can be problematic. German crews working in Tanganyika (present-day Tanzania) between 1909 and 1912 organized long convoys of native couriers to transport the fossils to the nearest port more than 435 km away. In the American West, fossil transport was entrusted to mules in the late 19th century. Today, there are trucks that provide transportation, or helicopters when funds allow.

Fossils in museums

Upon arrival at a museum, the fossils are entrusted to qualified personnel who will extract them from their rocky gangue and clean them. They must then be kept in special conditions. Frequent differences in temperature and humidity can damage some specimens, and insects can destroy labeling. They are therefore stored in closed windows often equipped with a system for controlling the temperature and the degree of humidity. Fossils belong to museums which, for the scientific community, are the easiest places to access. While most are never exposed, they are useful data sets for paleontologists. The ones presented are often the biggest or the most spectacular, but they are not necessarily the most interesting scientifically. Those that visitors do not see, on the other hand, provide the material on which paleontology is based to ensure its survival.

Laboratory work

The preparation of a new specimen is a long work of the highly specialized museum staff. Upon arrival at the laboratory, each fossil must be unpacked quickly so as not to allow the person who discovered it to forget the details of its exhumation. Then, the bones are cleaned and washed, and if necessary, arranged in the same way as at the time of their discovery (a sandbox is used for large bones). To reconstitute a big dinosaur, it is a little like making a puzzle in three dimensions without knowing the number of parts and without having model! The specimen must then be specially prepared before being studied or exhibited. There are several methods of preserving fossils based on specimens. Bones are often bound with special glues and should generally be kept at a constant temperature and humidity level.

The preparation

A fossil must first be cleared of the rocky gangue where it is located. This operation will depend on the nature of the fossil and the rock that surrounds it, as well as the study of which it will be the object and the place where it will be exposed. It is most often a mechanical or chemical preparation. In the first case, we use a dental drill and a small chisel to clear the fossil of its rocky gangue, and in the second, we remove the rock with a slightly acidic solution. Each method has its advantages and disadvantages. Tools such as saws, chisels and percussion instruments can seriously damage a fossil if they are not handled with care. They prevent the use of chemicals that can cause damage. If the bone (composed of calcium phosphate) is in a rock with a high calcium carbonate content such as limestone, a dilute acid will act on the rock without attacking the bone. An acidic solution can expose delicate structures that would be damaged if mechanically treated, but there is always the danger that the acid will enter the fossil and attack gradually from the inside. Preparing a dinosaur fossil is a specialist job that requires a lot of skill and patience. This person must work closely with a paleontologist who has the benefit of knowing the anatomy of dinosaurs. As the bone clears, she will record her observations and take photographs. To know the amount of rock to eliminate, she will only have to compare the bone she is working with those of other known dinosaurs. The preparation of a fossil can be extremely long, it can sometimes last for years while the extraction took a week.

The code of honor

Responsible researchers comply with a general regulation that protects important fossils and the rights of amateurs as individuals. Searching for fossils can be a nice hobby and paleontology is one of the few sciences where the contribution of passionate amateurs is precious, scientists can not do all the work alone. But fossils are not inexhaustible. How to make them benefit everyone? Fossil researchers know why they should not raid a site: everyone must be able to find something, without having to wait for erosion to expose new fossils, which can take a long time. Respecting the environment of the site is essential. Everyone should strive to minimize the effects of their presence on an area, by digging no more than is needed, returning each stone to its original position and leaving no debris.


Safety comes first and foremost, especially when you consider that in all sciences, field geology has the highest mortality rate. If the area is known for its poisonous plants or dangerous animals, learn to recognize them. Dress according to the weather: put on a long-sleeved shirt, sunglasses and protect your skin if the sun is warm. Drink a lot (at least 21 per day in the desert areas). Be careful in steep terrain and beware of thunderstorms. These precautionary tips are common sense, but in the excitement of the moment, it's one of the things we easily forget.

Fossils and the law

Laws relating to the collection and possession of fossils vary from one country to another, and even from one region to another in the same country. It is therefore important to contact the relevant authorities to inform you. If you intend to prospect on a private property, you will need to ask permission of the owner and agree with him on the perimeter to be searched, what you can take and what you can to do it. The collection of fossils on a public domain property may, in some places, be subject to restrictions or outright prohibited. The question of which fossils should be possessed by amateur or professional collectors has been debated at length. While most people agree that shellfish or shark teeth should be made available to schools, some are against selling to a private group such as a Tyrannosaurus skeleton. But sometimes the limit between what is acceptable and what is not is not so clearly defined. You always have the opportunity to contact amateur fossil research clubs or professional paleontologists in your area, who will be able to tell you if this or that fossil is worthy of inclusion in a museum collection. If you find a sample that may be of interest to a museum, such as a vertebrate animal bone, or that may be damaged if not handled by a professional, note its location as accurately as possible, photograph it on the site and contact the nearest museum.

Learn fossils

All we know or can surmise about dinosaurs and their way of life is based on the revelations of their fossil remains. Fossils are remnants of organisms. The work of paleontologists consists in reconstructing the life of animals that have disappeared from the traces they have left. Dinosaur fossils are among those most extensively studied.

Bone and skeleton

If fossilized bones are often found, whole skeletons are much rarer. These fossils allow paleontologists to construct theories and draw conclusions about the evolution of dinosaurs. Whole skeletons give a more complete picture than separate bones, but few are known to date. Most major groups include at least one dinosaur with a complete skeleton. These skeletons help to reconstruct the missing parts of other dinosaurs known only from fragmentary remains. Reconstructing an ancient creature from a collection of fossil vestiges remains a difficult task. For this, it is essential to unite only what goes together, and not to generalize from a single type of dinosaur. For example, the combination of an armored dinosaur plate with the tibia of a small carnivore and the sides of a long-necked herbivore would give a strange hybrid species unlike any of the dinosaurs that existed. This has happened sometimes.


Bones and other vestiges give by accumulation an idea of ​​the transformations that dinosaurs have undergone over time. In addition to the evidence provided by radiometric dating of rocks, transformations of bone structure can be used to reconstruct the history of dinosaur evolution. The starting point is the phylogenetic analysis by which paleontologists note the particular characteristics of the bones of different dinosaurs and study their relationships. The more commonalities these bones have together, the closer the two dinosaurs are. Transformations due to evolution are particularly interesting because they are not found in the ancestors. The crest of the bone of the forelimb, for example (pectoral crest) is unique to dinosaurs and is not found in any other group of animals. This suggests that dinosaurs are closer to each other than their immediate ancestors and other animals without this ridge. The more characteristics we have with an identical distribution, the more reliable the classification by groups.


Bones and skeletons are also the starting point for the physical reconstruction of the animal. The size of a bone gives an indication of the size of the dinosaur. The characteristics of these bones are indications of the use of the living animal. For example, the "hand" bones of a quadruped will be stronger than those of one of his bipedal parents. Likewise, sharp claws make it possible to cut or hold, while blunt claws are used to walk. Carnivores need sharp teeth to shred the flesh, and herbivores have grindstones to grind their food. The bones also provide important clues to the soft parts of the dinosaur that have not fossilized. Muscle attachments on bones leave marks. By studying their size and their position, we can understand the movements of the animal and deduce its power. The brain of the dinosaurs inside the skull, the size of the bone cavity can give a precise idea of ​​its appearance, even if it has not been fossilized. Nerves and blood vessels traveled through different bones, leaving behind them orifices indicating their passage. The fossilized bones can also show the diseases and injuries to which the animal has been subjected. An exhaustive list of diseases identified in dinosaurs, including arthritis, gout and various cancers, has been established from bone fossils. Injuries include fractures and nicks, traces of fighting between dinosaurs of the same species or with predators. The arrangement of the bones at the place where they were discovered is also very instructive. An intact skeleton proves that the corpse was quickly covered after the death of the animal, while scattered bones may indicate that the remains were eaten by scavengers. Isolated bones may have been carried away by a predator or carried into the waters of a river or by a flood.

Rare fossils

Many important indications about dinosaurs' lifestyles can be gleaned from fossil tracks (eggs, feces, footprints and tracks). The soft parts (feathers, skin, muscles and sometimes internal organs) are rarely preserved. They are quickly destroyed and exceptional circumstances are needed for them to become fossilized. The best-known feather samples are those of the Archaeopteryx, discovered in 1860. A series of bird and bird-like dinosaurs with their feathers and feather-like structures has been discovered more recently in China. Their carcasses were intact in extremely fine-grained sediments. Perhaps, at the death of the dinosaurs, they had fallen to the bottom of a lake or a sea where the lack of oxygen prevented the arrival of scavengers. The presence of feathers on the skeleton of these small theropods allows us to understand the origin of birds. Pieces of skin, or fingerprints left by the skin, have been found on several dinosaur fossils. They show us that most of them were covered with scales. If these fingerprints have been preserved, it is because the animal has sunk into the mud that has hardened on contact. The small theropod called Scipionyx from Italy provides the best example of preservation of internal organs. In this young specimen, the liver, intestines and various muscles were conversed. Some fossils from Liaoning, in northeastern China, have retained some internal organs, and in some skeletons, such as those of Seismosaurus, small pebbles, or gastroliths, have been found swallowed by the animal. These tell us the shape and location of the digestive system of these dinosaurs.

Nests, eggs and embryos

If the fossil discovery of eggs and dinosaur embryos is more than 100 years old, their detailed study is only about twenty years old. A wealth of information on the reproduction, development and behavior of dinosaurs has been provided to us. The spawning sites found in the United States, Argentina and Mongolia show us that the dinosaurs nested in huge colonies and return to their nest from one year to the next. Surprisingly, the nesting of dinosaurs resembles in many ways that of modern birds. The size of the adult dinosaur for example determined the size of the nest, as for birds today. The study of these nests shows that in some dinosaurs, the young remained there for a certain time after hatching eggs, and that their parents took care of them during this period. Other types of dinosaurs, on the other hand, apparently gave up their eggs as soon as they hatched them, leaving their little ones to fend for themselves.

Other fossils

The most curious dinosaur fossils are probably the coprolites, that is to say the remains of excrement. They show us what the dinosaurs ate and give an idea of ​​the structure of their lower digestive system. However, they provide few elements to associate them with their authors and their identification will probably never be confirmed. Another characteristic of coprolites is that they are often associated with coprophagous insects that have dug into feces and filled their furrows with dinosaur faeces. The footprints and tracks discovered to date concern the majority of large dinosaur groups and provide us with important clues about their mode of movement and their behavior. The spacing of footprints along a track tells us both the size of the animal and its speed of movement. Several tracks on the same site going in the same direction suggest that some dinosaurs moved in groups. This kind of site is rare, but it allows us to determine the composition and structure of the herd. In some cases, it is even a picture of dinosaur life that is preserved showing, for example, the flight of a herd of small dinosaurs in front of a predator or the pursuit of a larger prey by it. However, the association of footprints and tracks with the dinosaurs who are the authors is an imprecise science.