TYPES OF FOSSILS
AND WHAT THEY TELL US ABOUT THE DINOSAURS
Fossils can be divided into two categories, fossilized body parts (bones, claws, teeth, skin,
embryos, etc.) and fossilized traces, called ichnofossils (which are footprints, nests, dung,
toothmarks, etc.), that record the movements and behaviors of the dinosaurs.
The four types of fossils are:
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mold fossils (a fossilized impression made in the substrate - a negative image of the
organism)
cast fossils (formed when a mold is filled in)
trace fossils = ichnofossils (fossilized nests, gastroliths, burrows, footprints, etc.)
true form fossils (fossils of the actual animal or animal part).
There are six ways that organisms can turn into fossils, including:
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unaltered preservation (like insects or plant parts trapped in amber, a hardened form of tree
sap)
permineralization=petrification (in which rock-like minerals seep in slowly and replace
the original organic tissues with silica, calcite or pyrite, forming a rock-like fossil - can
preserve hard and soft parts - most bone and wood fossils are permineralized)
replacement (An organism's hard parts dissolve and are replaced by other minerals, like
calcite, silica, pyrite, or iron)
carbonization=coalification (in which only the carbon remains in the specimen - other
elements, like hydrogen, oxygen, and nitrogen are removed)
recrystalization (hard parts either revert to more stable minerals or small crystals turn into
larger crystals)
authigenic preservation (molds and casts of organisms that have been destroyed or
dissolved).
BODY FOSSILS
The most common body fossils found are from the hard parts of the body, including bones, claws
and teeth. More rarely, fossils have been found of softer body tissues. Body fossils include:

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Bones
- these fossils are the main means of learning about dinosaurs. The fossilized
bones of a tremendous number of species of dinosaurs have been found since 1818, when the
first dinosaur bone was discovered. The first nearly-complete skeleton (of Hadrosaurus
foulkii) was found in 1858 in New Jersey, USA.
Teeth and Claws - Sometimes a bit of a broken tooth of a carnivore is found with another
dinosaur's bones, especially those of herbivores. Lots of fossilized teeth have been found,
including those of Albertosaurus and Iguanodon
.
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Eggs
, Embryos
, and Nests - Fossilized dinosaur eggs were first found in France in
1869. Many fossilized dinosaur eggs have been found, at over 200 sites. Sometimes they
have preserved parts of embryos, which can help to match an egg with a species of dinosaur.
The embryo also sheds light on dinosaur development. The nests and clutches of eggs tells
much about dinosaurs' nurturing behavior. A dinosaur egg was found by a 3-year-old child.
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Skin - Some dinosaurs had thick, bumpy skin, like that of an alligator

. A 12-
year-old girl discovered a T. rex's
bumpy skin imprint, confirming that it had a
"lightly pebbled skin."
Muscles, Tendons, Organs, and Blood Vessels - These are extremely rare because these
soft tissues usually decay before fossilization takes place. Recently, a beautiful theropod
fossil, Scipionyx, was found with many impressions of soft tissue preserved. Also rare are
so-called dinosaur "mummies", fossilized imprints of dinosaur skin and other features. These
are not real mummies in which actual animal tissue is preserved, but fossils that look a bit
like mummies.
TRACE FOSSILS
Trace fossils (ichnofossils) record the movements and behaviors of the dinosaurs. There are many
types of trace fossils. Even the lack of trace fossils can yield information; the lack of tail-furrow
fossils indicates an erect tail stance for dinosaurs that were previously believed to have dragged
their tails.
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Trackways (sets of footprints)
- Dinosaur tracks, usually
made in mud or fine sand, have been found at over 1500 sites,
including quarries, coal mines, riverbeds, deserts, and
mountains. There are so many of these fossils because each
dinosaur made many tracks (but had only one skeleton) and
A Hadrosaur footprint.
because tracks fossilize well.
Fossil footprints have yielded information about:
o Speed and length of stride
o whether they walked on two or four legs
o the bone structure of the foot
o stalking behavior (a carnivore hunting a herd of herbivores)
o the existence of dinosaur herds and stampedes
o how the tail is carried (few tail tracks have been found, so tails were probably held
above the ground)
Unfortunately, linking a set of tracks with a particular species is often virtually impossible.
Although there were many more plant-eating dinosaurs (sauropods and ornithopods) than
meat-eating dinosaurs (theropods), many more footprints of meat-eaters have been found.
This may be because the meat-eaters walked in muddy areas (where footprints are more
likely to leave a good impression and fossilize) more frequently than the plant-eaters).
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Toothmarks - Toothmarks generally appear in bones
.
Gizzard Rocks
- Some dinosaurs swallowed stones to help grind their food (modern
birds do this also). These stones, called gastroliths (literally meaning stomach-stones), have
been found as fossils. They are usually smooth, polished, and rounded (and hard to
distinguish from river rocks.)
Coprolites (fossilized feces) - Coprolites yield information about the dinosaurs' diet and
habitats. Coprolites up to 40 cm (16 inches) in diameter have been found, probably from a
sauropod, considering its size. A huge theropod coprolite was recently found Sasketchewan,
Canada. The only meat-eater large enough in that area at that time was Tyrannosaurus rex.
Burrows and Nests - Fossils of dinosaurs' burrows and nests can reveal a lot about their
behavior.
What was the first fossil found?
First Dinosaur Fossil Discoveries
The first 3 dinosaur fossils led to the recognition of a new group of animals, the dinosaurs.
The first nearly-complete dinosaur skeleton in New Jersey spurs modern paleontology.
People have been finding dinosaur fossils for hundreds of years, probably even thousands of years.
The Greeks and Romans may have found fossils, giving rise to their many ogre and griffin legends.
There are references to "dragon" bones found in Wucheng, Sichuan, China (written by Chang Qu)
over 2,000 years ago; these were probably dinosaur fossils.
Much later, in 1676, a huge thigh bone (femur) was found in England by Reverend Plot. It was
thought that the bone belonged to a "giant," but was probably from a dinosaur. A report of this find
was published by R. Brookes in 1763.
The First Dinosaur Fossil Scientifically Described
The first dinosaur to be described scientifically was Megalosaurus. This genus
was named in 1824, by William Buckland; Gideon Mantell (not Ferdinand
August von Ritgen) assigned the scientific type species name, Megalosaurus
bucklandii. (Note: the first dinosaur found was Iguanodon, but it was named
and described later than Megalodon.) Buckland (1784-1856) was a British fossil hunter and
clergyman who discovered collected fossils.
It was the first dinosaur ever described scientifically and first theropod dinosaur discovered (this is
all in hindsight, because the dinosaurs had not yet been recognized as a separate taxonomic group the word dinosaur hadn't even been invented yet).
The first dinosaur models (life size and made of concrete) were made by Benjamin Waterhouse
Hawkins of England in 1854. The first dinosaur used for amusement was a life-size model of an
Iguanodon (made by Hawkins) that was used to house a dinner party for scientists (including
Richard Owen) at a major exhibition. The invitations to the party were sent on fake pterodactyl
wings. The party took place in London, England, in 1854
Other Early Dinosaur Finds
Gideon A. Mantell (1790-1852) was another early British fossil
hunter. He described and named Iguanodon, a duck-billed planteater (1825); Iguanodon's teeth and a few bones were found in
1822, perhaps by his wife, Mrs. Mary Mantell in Sussex,
IGUANODON (southern) England. Gideon Mantell also named Hylaeosaurus,
HYLAEOSAURUS
an armored plant-eater (1833) , and others.
The Name "Dinosauria"
Sir Richard Owen (1804-1892) was a pioneering British comparative anatomist who coined the
term dinosauria (from the Greek "deinos" meaning fearfully great, and "sauros" meaning lizard),
recognizing them as a suborder of large, extinct reptiles in 1841.
He had noticed that a group of fossils (which included remains of Megalosaurus, Iguanodon, and
Hylaeosaurus) had certain characteristics in common, including:
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Column-like legs
(instead of the sprawling legs
Five fused vertebrae fused to the pelvic girdle.
that other reptiles have)
Owen presented dinosaurs as a separate taxonomic group in order to bolster his arguments against
the newly proposed theory of evolution (although Darwin's "Origin of the Species" wasn't
published until 1859, the basic ideas of evolution were known, but its mechanisms, including
natural selection, were not). Ironically, his work actually helped support the evolutionists
arguments.
This new taxonomic name, Dinosauria, and new group of reptiles was only the beginning of a great
scientific exploration. Since Owen's time, about 330 dinosaur genera have been described. Every
few months (sometimes every few weeks), a new species is unearthed (for recent finds, see Dino
News). Paleontologists have varying estimates of how many dinosaur genera existed during the
Mesozoic Era; estimates range from about 1,000 to over 10,000. Whatever this number really is,
there are a lot of new dinosaurs left to discover!
The First Nearly-Complete Dinosaur Skeleton and First American
Dinosaur
The first dinosaur fossil found in the US was a thigh bone found by Dr. Caspar Wistar, in
Gloucester County, New Jersey, in 1787 (it has since been lost, but more fossils were later found in
the area).
In 1800 in Massachusetts, USA, Pliny Moody found 1-foot (31 cm) long
fossilized footprints at his farm that were thought by Harvard and Yale
scholars to be from "Noah's Raven." Many other dinosaur footprints were
been found in New England stone quarries in the early 1800's, but they were
thought to be unimportant and were blown up in the quarrying process. Other
fragmentary dinosaur bones and tracks were unearthed at this time in
A Hadrosaur footprint.
Connecticut Valley, Massachusetts.
The first nearly-complete dinosaur skeleton was discovered by William Parker Foulke. Foulke had
heard of a discovery made by workmen in a Cretaceous marl (a crumbly type of soil) pit on the
John E. Hopkins farm in Haddonfield, New Jersey beginning in 1838. Foulke heard of the
discovery and recognized its importance in 1858. Unfortunately, some of the bones had already
been removed by workmen. The skull-less dinosaur was excavated and named by US anatomist
Joseph Leidy who named it Hadrosaurus fouki (meaning "Foulke's big lizard"). It was a duck-billed
dinosaur (but it is now a doubtful genus because there is so little fossil information about it). The
"Haddonfield Hadrosaurus" is on display at the Philadelphia Academy of Natural Sciences.
Leidy's analysis of this Hadrosaur skeleton was thorough; from its anatomy, he wrote imaginitively
about the dinosaur's way of life and its death. Leidy wrote, "Hadrosaurus was most probably
amphibious; and though its remains were obtained from a marine deposit, the rarity of them in the
latter leads us to suppose that those in our possession had been carried down the current of a river,
upon whose banks the animals lived." (Quoted from J. Leidy, Account of the Remains of a Fossil
Reptile Recently Discovered at Haddonfield, New Jersey. Proceedings Academy of Natural
Sciences, Philadelphia, Dec. 14, 1858 pp.1-16.)
This study influenced the popular image of dinosaurs and dinosaur science for years. This
beautiful skeleton made dinosaurs come to life in peoples' imaginations and spurred generations
of paleontologists
How do fossils form?
HOW FOSSILS FORM
Fossils of hard mineral parts (like bones

and teeth) were formed as follows:
Some animals
were quickly buried after their death (by sinking in mud, being
buried in a sand storm, etc.).
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Over time, more and more sediment covered the remains.
The parts of the animals that didn't rot (usually the harder parts likes bones and teeth) were
encased in the newly-formed sediment.
In the right circumstances (no scavengers, quick burial, not much weathering), parts of the
animal turned into fossils over time.
After a long time, the chemicals in the buried animals' bodies underwent a series of changes.
As the bone slowly decayed, water infused with minerals seeped into the bone and replaced
the chemicals in the bone with rock-like minerals. The process of fossilization involves the
dissolving and replacement of the original minerals in the object with other minerals (and/or
permineralization, the filling up of spaces in fossils with minerals, and/or recrystallization in
which a mineral crystal changes its form).
This process results in a heavy, rock-like copy of the original object - a fossil. The fossil has
the same shape as the original object, but is chemically more like a rock! Some of the
original hydroxy-apatite (a major bone consitiuent) remains, although it is saturated with
silica (rock).
Here's a flow chart of fossil formation:
There are six ways that organisms can turn into fossils, including:






unaltered preservation (like insects or plant parts trapped in amber, a hardened form of tree
sap)
permineralization=petrification (in which rock-like minerals seep in slowly and replace
the original organic tissues with silica, calcite or pyrite, forming a rock-like fossil - can
preserve hard and soft parts - most bone and wood fossils are permineralized)
replacement (An organism's hard parts dissolve and are replaced by other minerals, like
calcite, silica, pyrite, or iron)
carbonization=coalification (in which only the carbon remains in the specimen - other
elements, like hydrogen, oxygen, and nitrogen are removed)
recrystalization (hard parts either revert to more stable minerals or small crystals turn into
larger crystals)
authigenic preservation (molds and casts of organisms that have been destroyed or
dissolved).
Most animals did not fossilize; they simply decayed and were lost from the fossil record.
Paleontologists estimate that only a small percentage of the dinosaur genera that ever lived have
been or will be found as fossils.
Most of the dinosaur skeletons that are shown in museums are not actually fossils! They are
lightweight fiberglass or resin replicas of the original fossils.
Why are Fossils Rock-Colored?
Because they ARE rocks! A fossilized object is just a rocky model of an ancient object. A fossil is
composed of different materials than the original object was. During the fossilization process, the
original atoms are replaced by new minerals, so a fossils doesn't have the same color (or chemical
composition) as the original object. Fossils come in many colors and are made of many different
types of minerals, depending on what the surrounding rock matrix was composed of; one dinosaur
bone (Minmi) is an opal.
Also, some fossils of skin (and other soft body parts) have been found. Again, the color of the skin
is not retained during the fossilization process, all that remains today is a rocky model of the
original.
What do fossils tell us about dinosaurs?
DATING FOSSILS
Dating individual fossils is a relatively straightforward (and approximate) process, outlined below.
After that comes a more difficult process: estimating the existence-span of an species. Finding a
fossil merely places one organism within a time span. Finding many organisms places the group
within a time span. Determining the actual existence-span of the species is very approximate. If the
fossils are relatively rare, the actual existence-span may be much greater that the fossil record
indicates. Even if the fossils are relatively abundant during the species' heyday, the number of
organisms may have been small during the time of its appearance on Earth and during its demise.
At these important times, its fossil record might be sparse or nil, causing those times to be underrepresented.
DATING INDIVIDUAL FOSSILS
Paleontologists use many ways of dating individual fossils in geologic time.
1. The oldest method is stratigraphy, studying how deeply a fossil is buried. Dinosaur fossils
are usually found in sedimentary rock. Sedimentary rock layers (strata) are formed
episodically as earth is deposited horizontally over time. Newer layers are formed on top of
older layers, pressurizing them into rocks. Paleontologists can estimate the amount of time
that has passed since the stratum containing the fossil was formed. Generally, deeper rocks
and fossils are older than those found above them.
2. Observations of the fluctuations of the Earth's magnetic field, which leaves different
magnetic fields in rocks from different geological eras.
3. Dating a fossil in terms of approximately how many years old it is can be
possible using radioisotope-dating of igneous rocks found near the fossil. Unstable
radioactive isotopes of elements, such as Uranium-235, decay at constant, known
rates over time (its half-life, which is over 700 million years). An accurate estimate of the
rock's age can be determined by examining the ratios of the remaining
radioactive element and its daughters. For example, when lava cools, it has no
lead content but it does contain some radioactive Uranium (U-235). Over time,
the unstable radioactive Uranium decays into its daughter, Lead-207, at a
constant, known rate (its half-life). By comparing the relative proportion of Uranium-235
and Lead-207, the age of the igneous rock can be determined. Potassium-40 (which decays
to argon-40) is also used to date fossils.
The half-life of carbon-14 is 5,568 years. That means that half of the C-14 decays (into
nitrogen-14) in 5,568 years. Half of the remaining C-14 decays in the next 5,568 years, etc.
This is too short a half-life to date dinosaurs; C-14 dating is useful for dating items up to
about 50,000 - 60,000 years ago (useful for dating organiams like Neanderthal man and ice
age animals).
Radioisotope dating cannot be used directly on fossils since they don't contain the unstable
radioactive isotopes used in the dating process. To determine a fossil's age, igneous layers
(volcanic rock) beneath the fossil (predating the fossil) and above it (representing a time
after the dinosaur's existence) are dated, resulting in a time-range for the dinosaur's life.
Thus, dinosaurs are dated with respect to volcanic eruptions.
4. Looking for index fossils - Certain common fossils are important in determining ancient
biological history. These fossil are widely distributed around the Earth but limited in time
span. Examples of index fossils include brachiopods (which appeared in the Cambrian
period), trilobites (which probably originated in the pre-Cambrian or early Paleozoic and are
common throughout the Paleozoic layer - about half of Paleozoic fossils are trilobites),
ammonites (from the Triassic and Jurassic periods, and went extinct during the K-T
extinction), many nanofossils (microscopic fossils from various eras which are widely
distributed, abundant, and time-specific)
FINDING FOSSILS: SKILL, TENACITY, AND LUCK
Since fossils are buried during their formation, finding them can be difficult. Paleontologists do a
lot of research to decide where to dig
for a dig, they choose:
for dinosaurs
. To choose an optimal location



sedimentary rock
- shale, sandstone, or limestone (this is where most fossils were
preserved),
a sedimentary layer from the Mesozoic Era (when the dinosaurs lived). Exposed sedimentary
rock is pretty easy to identify - it's in layers. To find an example of exposed sedimentary
rock in your area, look at the cut-out area where highways go through hills. The layers
should be easily visible. Other places to look are cliffs, rock outcroppings, canyons,
badlands, etc.,
a place that was not an ocean or lake during the Mesozoic, because the dinosaurs lived only
on land.
Areas where fossil-bearing sedimentary rock erode quickly (because of rain, flooding, wind, etc.)
are good for finding fossils. Rarely, fossils are observed just sticking out of the ground. More often,
paleontologists must do enormous amounts of work to find, excavate
, and prepare fossils.
The Continents
Fossils have been found on every continent on Earth
. Rock strata in many places are
remarkably similar to each other. This lends credence to the continental drift theory of Alfred
Wegener (1912) who theorized that 200 million years ago there was a single land mass on Earth
which he called "Pangaea" (meaning "All Earth"). This land mass then slowly drifted apart on
Earth's floating crust, forming separate continents. Wegener's theory explains why fossils of the
same species are found on many different, unconnected continents.
How do you dig a fossil?
Excavating Fossils
After being found, a fossil must be carefully freed from the rocky matrix that encased it
for millions of years without damaging it. First the fossils should be labelled and
photographed (while still encased in the rock). Its position should be carefully noted.
Most of the overlying rock (the overburden) is removed using large tools (like picks and
shovels), but the 2-3 inches (5-8 cm) of rock closest to the fossil are removed with
smaller hand tools (like trowels, hammers, whisks, and dental tools). The exposed fossil
is photographed and labeled again. Frequently, only some of the overlying rock is
removed at the dig site. The rest of the overburden can be removed later, in the lab.
Small fossils are easily excavated with small hand tools. Large fossils require more effort
and bigger tools in order to expose the specimen; these tools include shovels, picks, jackhammers, or even explosives.
Small and large fossils are excavated differently, but both have to be treated very carefully to
avoid breaking them. Before removing a crumbling or fragile fossil, a quick-setting glue can be
applied to it (with a brush or sprayer). Then the fossil can be removed from the surrounding
rock.
The fossil must be packed very carefully to be moved to the lab. Small fossils can be packed in
boxes or bags. Large fossils can be first wrapped in paper or burlap, with a layer of plaster
applied (like setting a broken bone).
What is a fossil?
WHAT ARE FOSSILS
AND WHAT IS PALEONTOLOGY?
The only direct way we have of learning about dinosaurs
is by studying fossils. Fossils are
the remains of ancient animals and plants, the traces or impressions of living things from past
geologic ages, or the traces of their activities. Fossils have been found on every continent on Earth,
maybe even near where you live.
The word fossil comes from the Latin word fossilis, which means "dug up." Most fossils are
excavated
from sedimentary rock layers
. Sedimentary rock is rock that has formed
from sediment, like sand, mud, small pieces of rocks. Over long periods of time, these small pieces
of debris are compressed (squeezed) as they are buried under more and more layers of sediment
that piles up on top of it. Eventually, they are compressed into sedimentary rock. The layers that are
farther down in the Earth are older than the top layers.
The fossil of a bone
doesn't have any bone in it! A fossilized object has the same shape as the
original object, but is chemically more like a rock.
Paleontology is the branch of biology that studies the forms of life that existed in former
geologic periods, chiefly by studying fossils.
What Do Fossils Look Like?
Fossils have the same shape that the original item had, but their color, density, and texture vary
widely. A fossil's color depends on what minerals formed it. Fossils are usually heavier than the
original item since they are formed entirely of minerals (they're essentially stone that has replaced
the original structure). Most fossils are made of ordinary rock material, but some are more exotic,
including one fossilized dinosaur bone, a Kakuru tibia, which is an opal!