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!
HOW FOSSILS FORM
Fossils of hard mineral parts (like bones
and teeth) were formed as follows:
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Some animals
were quickly buried after their death (by sinking
in mud, being buried in a sand storm, etc.).
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:
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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
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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.
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.
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,
A Hadrosaur footprint.
riverbeds, deserts, and mountains. There are
so many of these fossils because each dinosaur made many tracks (but
had only one skeleton) and 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
o
o
o
the bone structure of the foot
stalking behavior (a carnivore hunting a herd of herbivores)
the existence of dinosaur herds and stampedes
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 fottprints are more likely to
leave a good impression and fossilize) more frequently than the planteaters).
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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.
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
. To choose an optimal location for a dig, they choose:
for dinosaurs
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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.
Children and Fossils
Children have found important dinosaur fossils, including T. rex
found by a 12-year-old and an egg found by a 3-year-old.
Fossil Hot Spots: Lagerstätten
Lagerstätten (meaning "fossil deposit places" in German) are geological
skin
deposits that are rich with varied, well-preserved fossils, representing a wide
variety of life from a particular era. These spectacular fossil deposits represent
an amazing "snapshot" in time. Some Lagerstätten include the La Brea Tar Pits
(California, USA), Ediacara Hills (South Australia), Burgess Shale (B.C.,
Canada), Solnhofen (Germany), and Mazon Creek (Illinois, USA)
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 C14 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), etc.
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, jack-hammers, 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).
First Dinosaur Fossil Discoveries
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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. Buckland (1784-1856) was a British fossil hunter and clergyman
who discovered collected fossils. (Note: the first dinosaur found was
Iguanodon, but it was named and described later than Megalodon.)
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 plant-eater
(1825); Iguanodon's teeth and a few bones
were found in 1822, perhaps by his wife,
IGUANODON Mrs. Mary Mantell in Sussex, (southern)
HYLAEOSAURUS
England. Gideon Mantell also named
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 1842.
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
reptiles have)
Five fused vertebrae fused to the pelvic girdle.
that other
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 1foot (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
A Hadrosaur footprint.
were blown up in the quarrying process. Other
fragmentary dinosaur bones and tracks were unearthed at this time in
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.
Taken from Encarta 2008