A fossil (from Classical
Latin fossilis; literally, "obtained by
digging") is any preserved remains, impression, or trace of any
once-living thing from a past geological age. Examples include bones,
shells, exoskeletons, stone imprints of animals or microbes, hair,
petrified wood, oil, coal, and
DNA remnants. The totality of fossils
is known as the fossil record.
Paleontology is the study of fossils: their age, method of formation,
and evolutionary significance. Specimens are usually considered to be
fossils if they are over 10,000 years old. The oldest fossils
are from around 3.48 billion years old to 4.1
billion years old. The observation in the 19th century that
certain fossils were associated with certain rock strata led to the
recognition of a geological timescale and the relative ages of
different fossils. The development of radiometric dating techniques in
the early 20th century allowed scientists to quantitatively measure
the absolute ages of rocks and the fossils they host.
There are many processes that lead to fossilization, including
permineralization, casts and molds, authigenic mineralization,
replacement and recrystallization, adpression, carbonization, and
Fossil of an
Fossils vary in size from one micrometer bacteria  to dinosaurs and
trees, many meters long and weighing many tons. A fossil normally
preserves only a portion of the deceased organism, usually that
portion that was partially mineralized during life, such as the bones
and teeth of vertebrates, or the chitinous or calcareous exoskeletons
Fossils may also consist of the marks left behind by
the organism while it was alive, such as animal tracks or feces
(coprolites). These types of fossil are called trace fossils or
ichnofossils, as opposed to body fossils. Some fossils are biochemical
and are called chemofossils or biosignatures.
1.2 Casts and molds
1.3 Authigenic mineralization
1.4 Replacement and recrystallization
1.5 Adpression (compression-impression)
1.5.1 Soft tissue, cell and molecular preservation
2.1 Estimating dates
4.9 Chemical fossils
7 History of the study of fossils
7.1 Before Darwin
7.2 Linnaeus and Darwin
7.3 After Darwin
7.4 Modern era
8 Trading and collecting
10 See also
12 Further reading
13 External links
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The process of fossilization varies according to tissue type and
Silicified (replaced with silica) fossils from the Road Canyon
Permian of Texas).
Permineralization is a process of fossilization that occurs when an
organism is buried. The empty spaces within an organism (spaces filled
with liquid or gas during life) become filled with mineral-rich
groundwater. Minerals precipitate from the groundwater, occupying the
empty spaces. This process can occur in very small spaces, such as
within the cell wall of a plant cell. Small scale permineralization
can produce very detailed fossils. For permineralization to occur, the
organism must become covered by sediment soon after death or soon
after the initial decay process. The degree to which the remains are
decayed when covered determines the later details of the fossil. Some
fossils consist only of skeletal remains or teeth; other fossils
contain traces of skin, feathers or even soft tissues. This is a form
Casts and molds
External mold of a bivalve from the Logan Formation, Lower
In some cases the original remains of the organism completely dissolve
or are otherwise destroyed. The remaining organism-shaped hole in the
rock is called an external mold. If this hole is later filled with
other minerals, it is a cast. An endocast or internal mold is formed
when sediments or minerals fill the internal cavity of an organism,
such as the inside of a bivalve or snail or the hollow of a skull.
This is a special form of cast and mold formation. If the chemistry is
right, the organism (or fragment of organism) can act as a nucleus for
the precipitation of minerals such as siderite, resulting in a nodule
forming around it. If this happens rapidly before significant decay to
the organic tissue, very fine three-dimensional morphological detail
can be preserved. Nodules from the
Mazon Creek fossil
beds of Illinois, USA, are among the best documented examples of such
Replacement and recrystallization
Recrystallized scleractinian coral (aragonite to calcite) from the
Jurassic of southern Israel
Replacement occurs when the shell, bone or other tissue is replaced
with another mineral. In some cases mineral replacement of the
original shell occurs so gradually and at such fine scales that
microstructural features are preserved despite the total loss of
original material. A shell is said to be recrystallized when the
original skeletal compounds are still present but in a different
crystal form, as from aragonite to calcite.
Compression fossils, such as those of fossil ferns, are the result of
chemical reduction of the complex organic molecules composing the
organism's tissues. In this case the fossil consists of original
material, albeit in a geochemically altered state. This chemical
change is an expression of diagenesis. Often what remains is a
carbonaceous film known as a phytoleim, in which case the fossil is
known as a compression. Often, however, the phytoleim is lost and all
that remains is an impression of the organism in the rock—an
impression fossil. In many cases, however, compressions and
impressions occur together. For instance, when the rock is broken
open, the phytoleim will often be attached to one part (compression),
whereas the counterpart will just be an impression. For this reason,
one term covers the two modes of preservation: adpression.
Soft tissue, cell and molecular preservation
Because of their antiquity, an unexpected exception to the alteration
of an organism's tissues by chemical reduction of the complex organic
molecules during fossilization has been the discovery of soft tissue
in dinosaur fossils, including blood vessels, and the isolation of
proteins and evidence for
DNA fragments. In 2014, Mary
Schweitzer and her colleagues reported the presence of iron particles
(goethite-aFeO(OH)) associated with soft tissues recovered from
dinosaur fossils. Based on various experiments that studied the
interaction of iron in haemoglobin with blood vessel tissue they
proposed that solution hypoxia coupled with iron chelation enhances
the stability and preservation of soft tissue and provides the basis
for an explanation for the unforeseen preservation of fossil soft
tissues. However, a slightly older study based on eight taxa
ranging in time from the
Devonian to the
Jurassic found that
reasonably well-preserved fibrils that probably represent collagen
were preserved in all these fossils, and that the quality of
preservation depended mostly on the arrangement of the collagen
fibers, with tight packing favoring good preservation. There
seemed to be no correlation between geological age and quality of
preservation, within that timeframe.
Carbonaceous films are thin coatings which consist predominantly of
the chemical element carbon. The soft tissues of organisms are made
largely of organic carbon compounds and during diagenesis under
reducing conditions only a thin film of carbon residue is left which
forms a silhouette of the original organism.
The star-shaped holes (Catellocaula vallata) in this Upper Ordovician
bryozoan represent a soft-bodied organism preserved by bioimmuration
in the bryozoan skeleton.
Bioimmuration occurs when a skeletal organism overgrows or otherwise
subsumes another organism, preserving the latter, or an impression of
it, within the skeleton. Usually it is a sessile skeletal
organism, such as a bryozoan or an oyster, which grows along a
substrate, covering other sessile sclerobionts. Sometimes the
bioimmured organism is soft-bodied and is then preserved in negative
relief as a kind of external mold. There are also cases where an
organism settles on top of a living skeletal organism that grows
upwards, preserving the settler in its skeleton. Bioimmuration is
known in the fossil record from the Ordovician to the Recent.
Geochronology and Relative dating
Paleontology seeks to map out how life evolved across geologic time. A
substantial hurdle is the difficulty of working out fossil ages. Beds
that preserve fossils typically lack the radioactive elements needed
for radiometric dating. This technique is our only means of giving
rocks greater than about 50 million years old an absolute age,
and can be accurate to within 0.5% or better. Although radiometric
dating requires careful laboratory work, its basic principle is
simple: the rates at which various radioactive elements decay are
known, and so the ratio of the radioactive element to its decay
products shows how long ago the radioactive element was incorporated
into the rock. Radioactive elements are common only in rocks with a
volcanic origin, and so the only fossil-bearing rocks that can be
dated radiometrically are volcanic ash layers, which may provide
termini for the intervening sediments.
Consequently, palaeontologists rely on stratgraphy to date fossils.
Stratigraphy is the science of deciphering the "layer-cake" that is
the sedimentary record. Rocks normally form relatively horizontal
layers, with each layer younger than the one underneath it. If a
fossil is found between two layers whose ages are known, the fossil's
age is claimed to lie between the two known ages. Because rock
sequences are not continuous, but may be broken up by faults or
periods of erosion, it is very difficult to match up rock beds that
are not directly adjacent. However, fossils of species that survived
for a relatively short time can be used to match isolated rocks: this
technique is called biostratigraphy. For instance, the conodont
Eoplacognathus pseudoplanus has a short range in the Middle Ordovician
period. If rocks of unknown age have traces of E. pseudoplanus,
they have a mid-
Ordovician age. Such index fossils must be
distinctive, be globally distributed and occupy a short time range to
be useful. Misleading results are produced if the index fossils are
Stratigraphy and biostratigraphy can in general
provide only relative dating (A was before B), which is often
sufficient for studying evolution. However, this is difficult for some
time periods, because of the problems involved in matching rocks of
the same age across continents. Family-tree relationships also
help to narrow down the date when lineages first appeared. For
instance, if fossils of B or C date to X million years ago and
the calculated "family tree" says A was an ancestor of B and C, then A
must have evolved earlier.
It is also possible to estimate how long ago two living clades
diverged, in other words approximately how long ago their last common
ancestor must have lived, by assuming that
DNA mutations accumulate at
a constant rate. These "molecular clocks", however, are fallible, and
provide only approximate timing: for example, they are not
sufficiently precise and reliable for estimating when the groups that
feature in the
Cambrian explosion first evolved, and estimates
produced by different techniques may vary by a factor of two.
Further information: Ghost lineage, Signor–Lipps effect, and
Some of the most remarkable gaps in the fossil record (as of October
2013) show slanting toward organisms with hard parts
Organisms are only rarely preserved as fossils in the best of
circumstances, and only a fraction of such fossils have been
discovered. This is illustrated by the fact that the number of species
known through the fossil record is less than 5% of the number of known
living species, suggesting that the number of species known through
fossils must be far less than 1% of all the species that have ever
lived. Because of the specialized and rare circumstances required
for a biological structure to fossilize, only a small percentage of
life-forms can be expected to be represented in discoveries, and each
discovery represents only a snapshot of the process of evolution. The
transition itself can only be illustrated and corroborated by
transitional fossils, which will never demonstrate an exact half-way
The fossil record is strongly biased toward organisms with hard-parts,
leaving most groups of soft-bodied organisms with little to no
role. It is replete with the mollusks, the vertebrates, the
echinoderms, the brachiopods and some groups of arthropods.
Main article: Lagerstätte
Further information: List of fossil sites
Fossil sites with exceptional preservation—sometimes including
preserved soft tissues—are known as Lagerstätten - German for
"storage places". These formations may have resulted from carcass
burial in an anoxic environment with minimal bacteria, thus slowing
decomposition. Lagerstätten span geological time from the Cambrian
period to the present. Worldwide, some of the best examples of
near-perfect fossilization are the
Maotianshan shales and
Burgess Shale, the
Devonian Hunsrück Slates, the
limestone, and the
Mazon Creek localities.
Main article: Stromatolites
Stromatolites from Bolivia, South America
Stromatolites are layered accretionary structures formed in shallow
water by the trapping, binding and cementation of sedimentary grains
by biofilms of microorganisms, especially cyanobacteria.
Stromatolites provide some of the most ancient fossil records of life
on Earth, dating back more than 3.5 billion years ago.
Stromatolites were much more abundant in Precambrian times. While
Archean fossil remains are presumed to be colonies of
cyanobacteria, younger (that is, Proterozoic) fossils may be
primordial forms of the eukaryote chlorophytes (that is, green algae).
One genus of stromatolite very common in the geologic record is
Collenia. The earliest stromatolite of confirmed microbial origin
dates to 2.724 billion years ago.
A 2009 discovery provides strong evidence of microbial stromatolites
extending as far back as 3.45 billion years ago.
Stromatolites are a major constituent of the fossil record for life's
first 3.5 billion years, peaking about 1.25 billion years ago.
They subsequently declined in abundance and diversity, which by
the start of the
Cambrian had fallen to 20% of their peak. The most
widely supported explanation is that stromatolite builders fell
victims to grazing creatures (the
Cambrian substrate revolution),
implying that sufficiently complex organisms were common over 1
billion years ago.
The connection between grazer and stromatolite abundance is well
documented in the younger
Ordovician evolutionary radiation;
stromatolite abundance also increased after the end-
Permian extinctions decimated marine animals, falling back to
earlier levels as marine animals recovered. Fluctuations in
metazoan population and diversity may not have been the only factor in
the reduction in stromatolite abundance. Factors such as the chemistry
of the environment may have been responsible for changes.
While prokaryotic cyanobacteria themselves reproduce asexually through
cell division, they were instrumental in priming the environment for
the evolutionary development of more complex eukaryotic organisms.
Cyanobacteria (as well as extremophile Gammaproteobacteria) are
thought to be largely responsible for increasing the amount of oxygen
in the primeval earth's atmosphere through their continuing
Cyanobacteria use water, carbon dioxide and sunlight
to create their food. A layer of mucus often forms over mats of
cyanobacterial cells. In modern microbial mats, debris from the
surrounding habitat can become trapped within the mucus, which can be
cemented by the calcium carbonate to grow thin laminations of
limestone. These laminations can accrete over time, resulting in the
banded pattern common to stromatolites. The domal morphology of
biological stromatolites is the result of the vertical growth
necessary for the continued infiltration of sunlight to the organisms
for photosynthesis. Layered spherical growth structures termed
oncolites are similar to stromatolites and are also known from the
fossil record. Thrombolites are poorly laminated or non-laminated
clotted structures formed by cyanobacteria common in the fossil record
and in modern sediments.
River Canyon area of the Kubis platform in the deeply
dissected Zaris Mountains of south western
Namibia provides an
extremely well exposed example of the
thrombolite-stromatolite-metazoan reefs that developed during the
Proterozoic period, the stromatolites here being better developed in
updip locations under conditions of higher current velocities and
greater sediment influx.
Main article: Index fossil
Examples of index fossils
Index fossils (also known as guide fossils, indicator fossils or zone
fossils) are fossils used to define and identify geologic periods (or
faunal stages). They work on the premise that, although different
sediments may look different depending on the conditions under which
they were deposited, they may include the remains of the same species
of fossil. The shorter the species' time range, the more precisely
different sediments can be correlated, and so rapidly evolving
species' fossils are particularly valuable. The best index fossils are
common, easy to identify at species level and have a broad
distribution—otherwise the likelihood of finding and recognizing one
in the two sediments is poor.
Main article: Trace fossil
Cambrian trace fossils including Rusophycus, made by a trilobite
A coprolite of a carnivorous dinosaur found in southwestern
Trace fossils consist mainly of tracks and burrows, but also include
coprolites (fossil feces) and marks left by feeding. Trace
fossils are particularly significant because they represent a data
source that is not limited to animals with easily fossilized hard
parts, and they reflect animal behaviours. Many traces date from
significantly earlier than the body fossils of animals that are
thought to have been capable of making them. Whilst exact
assignment of trace fossils to their makers is generally impossible,
traces may for example provide the earliest physical evidence of the
appearance of moderately complex animals (comparable to
Coprolites are classified as trace fossils as opposed to body fossils,
as they give evidence for the animal's behaviour (in this case, diet)
rather than morphology. They were first described by William Buckland
in 1829. Prior to this they were known as "fossil fir cones" and
"bezoar stones." They serve a valuable purpose in paleontology because
they provide direct evidence of the predation and diet of extinct
organisms. Coprolites may range in size from a few millimetres to
over 60 centimetres.
Main article: Transitional fossil
Further information: List of transitional fossils
A transitional fossil is any fossilized remains of a life form that
exhibits traits common to both an ancestral group and its derived
descendant group. This is especially important where the
descendant group is sharply differentiated by gross anatomy and mode
of living from the ancestral group. Because of the incompleteness of
the fossil record, there is usually no way to know exactly how close a
transitional fossil is to the point of divergence. These fossils serve
as a reminder that taxonomic divisions are human constructs that have
been imposed in hindsight on a continuum of variation.
Microfossils about 1 mm
Main article: Micropaleontology
Microfossil is a descriptive term applied to fossilized plants and
animals whose size is just at or below the level at which the fossil
can be analyzed by the naked eye. A commonly applied cutoff point
between "micro" and "macro" fossils is 1 mm. Microfossils may
either be complete (or near-complete) organisms in themselves (such as
the marine plankters foraminifera and coccolithophores) or component
parts (such as small teeth or spores) of larger animals or plants.
Microfossils are of critical importance as a reservoir of paleoclimate
information, and are also commonly used by biostratigraphers to assist
in the correlation of rock units.
Main article: Amber
Leptofoenus pittfieldae trapped in Dominican amber, from 20 to
16 million years ago
Fossil resin (colloquially called amber) is a natural polymer found in
many types of strata throughout the world, even the Arctic. The oldest
fossil resin dates to the Triassic, though most dates to the Cenozoic.
The excretion of the resin by certain plants is thought to be an
evolutionary adaptation for protection from insects and to seal
Fossil resin often contains other fossils called inclusions
that were captured by the sticky resin. These include bacteria, fungi,
other plants, and animals.
Animal inclusions are usually small
invertebrates, predominantly arthropods such as insects and spiders,
and only extremely rarely a vertebrate such as a small lizard.
Preservation of inclusions can be exquisite, including small fragments
See also: Zombie taxon
Jurassic plesiosaur vertebral centrum found in the Lower
Cretaceous Faringdon Sponge Gravels in Faringdon, England. An example
of a remanié fossil.
A derived, reworked or remanié fossil is a fossil found in rock that
accumulated significantly later than when the fossilized animal or
plant died. Reworked fossils are created by erosion exhuming
(freeing) fossils from the rock formation in which they were
originally deposited and their redeposition in an younger sedimentary
Petrified wood. The internal structure of the tree and bark are
maintained in the permineralization process.
Polished section of petrified wood showing annual rings.
Fossil wood is wood that is preserved in the fossil record. Wood is
usually the part of a plant that is best preserved (and most easily
Fossil wood may or may not be petrified. The fossil wood may
be the only part of the plant that has been preserved: therefore
such wood may get a special kind of botanical name. This will usually
include "xylon" and a term indicating its presumed affinity, such as
Araucarioxylon (wood of
Araucaria or some related genus), Palmoxylon
(wood of an indeterminate palm), or Castanoxylon (wood of an
Main article: Subfossil
A subfossil dodo skeleton
The term subfossil can be used to refer to remains, such as bones,
nests, or defecations, whose fossilization process is not complete,
either because the length of time since the animal involved was living
is too short (less than 10,000 years) or because the conditions in
which the remains were buried were not optimal for fossilization.
Subfossils are often found in caves or other shelters where they can
be preserved for thousands of years. The main importance of
subfossil vs. fossil remains is that the former contain organic
material, which can be used for radiocarbon dating or extraction and
sequencing of DNA, protein, or other biomolecules. Additionally,
isotope ratios can provide much information about the ecological
conditions under which extinct animals lived. Subfossils are useful
for studying the evolutionary history of an environment and can be
important to studies in paleoclimatology.
Subfossils are often found in depositionary environments, such as lake
sediments, oceanic sediments, and soils. Once deposited, physical and
chemical weathering can alter the state of preservation.
See also: Biosignature
Chemical fossils, or chemofossils, are chemicals found in rocks and
fossil fuels (petroleum, coal, and natural gas) that provide an
organic signature for ancient life. Molecular fossils and isotope
ratios represent two types of chemical fossils. The oldest traces
of life on Earth are fossils of this type, including carbon isotope
anomalies found in zircons that imply the existence of life as early
as 4.1 billion years ago.
It has been suggested that biominerals could be important indicators
of extraterrestrial life and thus could play an important role in the
search for past or present life on the planet Mars. Furthermore,
organic components (biosignatures) that are often associated with
biominerals are believed to play crucial roles in both pre-biotic and
On 24 January 2014,
NASA reported that current studies by the
Curiosity and Opportunity rovers on
Mars will now be searching for
evidence of ancient life, including a biosphere based on autotrophic,
chemotrophic and/or chemolithoautotrophic microorganisms, as well as
ancient water, including fluvio-lacustrine environments (plains
related to ancient rivers or lakes) that may have been
habitable. The search for evidence of habitability,
taphonomy (related to fossils), and organic carbon on the planet Mars
is now a primary
An example of a pseudofossil: Manganese dendrites on a limestone
bedding plane from Solnhofen, Germany; scale in mm
Main article: Pseudofossils
Pseudofossils are visual patterns in rocks that are produced by
geologic processes rather than biologic processes. They can easily be
mistaken for real fossils. Some pseudofossils, such as dendrites, are
formed by naturally occurring fissures in the rock that get filled up
by percolating minerals. Other types of pseudofossils are kidney ore
(round shapes in iron ore) and moss agates, which look like moss or
plant leaves. Concretions, spherical or ovoid-shaped nodules found in
some sedimentary strata, were once thought to be dinosaur eggs, and
are often mistaken for fossils as well.
History of the study of fossils
Main article: History of paleontology
See also: Timeline of paleontology
Gathering fossils dates at least to the beginning of recorded history.
The fossils themselves are referred to as the fossil record. The
fossil record was one of the early sources of data underlying the
study of evolution and continues to be relevant to the history of life
on Earth. Paleontologists examine the fossil record to understand the
process of evolution and the way particular species have evolved.
Many early explanations relied on folktales or mythologies. In China
the fossil bones of ancient mammals including
Homo erectus were often
mistaken for "dragon bones" and used as medicine and aphrodisiacs. In
the West fossilized sea creatures on mountainsides were seen as proof
of the biblical deluge.
In 1027, the Persian
Avicenna explained fossils' stoniness in The Book
If what is said concerning the petrifaction of animals and plants is
true, the cause of this (phenomenon) is a powerful mineralizing and
petrifying virtue which arises in certain stony spots, or emanates
suddenly from the earth during earthquake and subsidences, and
petrifies whatever comes into contact with it. As a matter of fact,
the petrifaction of the bodies of plants and animals is not more
extraordinary than the transformation of waters.
Aristotle realized that fossil seashells from rocks were
similar to those found on the beach, indicating the fossils were once
Aristotle previously explained it in terms of vaporous
Avicenna modified into the theory of petrifying
fluids (succus lapidificatus), later elaborated by Albert of Saxony in
the 14th century and accepted in some form by most naturalists by the
More scientific views of fossils emerged during the Renaissance.
Leonardo da Vinci
Leonardo da Vinci concurred with Aristotle's view that fossils were
the remains of ancient life. For example, da Vinci noticed
discrepancies with the biblical flood narrative as an explanation for
If the Deluge had carried the shells for distances of three and four
hundred miles from the sea it would have carried them mixed with
various other natural objects all heaped up together; but even at such
distances from the sea we see the oysters all together and also the
shellfish and the cuttlefish and all the other shells which congregate
together, found all together dead; and the solitary shells are found
apart from one another as we see them every day on the sea-shores.
And we find oysters together in very large families, among which some
may be seen with their shells still joined together, indicating that
they were left there by the sea and that they were still living when
the strait of Gibraltar was cut through. In the mountains of Parma and
Piacenza multitudes of shells and corals with holes may be seen still
sticking to the rocks...."
Plesiosaurus from the 1834 Czech edition of Cuvier's
Discours sur les revolutions de la surface du globe.
Robert Hooke (1635-1703) included micrographs of fossils in his
Micrographia and was among the first to observe fossil forams. His
observations on fossils, which he stated to be the petrified remains
of creatures some of which no longer existed, were published
posthumously in 1705.
William Smith (1769–1839), an English canal engineer, observed that
rocks of different ages (based on the law of superposition) preserved
different assemblages of fossils, and that these assemblages succeeded
one another in a regular and determinable order. He observed that
rocks from distant locations could be correlated based on the fossils
they contained. He termed this the principle of faunal succession.
This principle became one of Darwin's chief pieces of evidence that
biological evolution was real.
Georges Cuvier came to believe that most if not all the animal fossils
he examined were remains of extinct species. This led Cuvier to become
an active proponent of the geological school of thought called
catastrophism. Near the end of his 1796 paper on living and fossil
elephants he said:
All of these facts, consistent among themselves, and not opposed by
any report, seem to me to prove the existence of a world previous to
ours, destroyed by some kind of catastrophe.
Linnaeus and Darwin
Early naturalists well understood the similarities and differences of
living species leading Linnaeus to develop a hierarchical
classification system still in use today. Darwin and his
contemporaries first linked the hierarchical structure of the tree of
life with the then very sparse fossil record. Darwin eloquently
described a process of descent with modification, or evolution,
whereby organisms either adapt to natural and changing environmental
pressures, or they perish.
When Darwin wrote On the Origin of
Species by Means of Natural
Selection, or the Preservation of Favoured Races in the Struggle for
Life, the oldest animal fossils were those from the
now known to be about 540 million years old. He worried about the
absence of older fossils because of the implications on the validity
of his theories, but he expressed hope that such fossils would be
found, noting that: "only a small portion of the world is known with
accuracy." Darwin also pondered the sudden appearance of many groups
(i.e. phyla) in the oldest known
Cambrian fossiliferous strata.
Since Darwin's time, the fossil record has been extended to between
2.3 and 3.5 billion years. Most of these Precambrian fossils
are microscopic bacteria or microfossils. However, macroscopic fossils
are now known from the late Proterozoic. The
Ediacara biota (also
called Vendian biota) dating from 575 million years ago
collectively constitutes a richly diverse assembly of early
The fossil record and faunal succession form the basis of the science
of biostratigraphy or determining the age of rocks based on embedded
fossils. For the first 150 years of geology, biostratigraphy and
superposition were the only means for determining the relative age of
rocks. The geologic time scale was developed based on the relative
ages of rock strata as determined by the early paleontologists and
Since the early years of the twentieth century, absolute dating
methods, such as radiometric dating (including potassium/argon,
argon/argon, uranium series, and, for very recent fossils, radiocarbon
dating) have been used to verify the relative ages obtained by fossils
and to provide absolute ages for many fossils.
Radiometric dating has
shown that the earliest known stromatolites are over 3.4 billion
The fossil record is life's evolutionary epic that unfolded over
four billion years as environmental conditions and genetic
potential interacted in accordance with natural selection.
Paleontology has joined with evolutionary biology to share the
interdisciplinary task of outlining the tree of life, which inevitably
leads backwards in time to Precambrian microscopic life when cell
structure and functions evolved. Earth's deep time in the Proterozoic
and deeper still in the
Archean is only "recounted by microscopic
fossils and subtle chemical signals." Molecular biologists, using
phylogenetics, can compare protein amino acid or nucleotide sequence
homology (i.e., similarity) to evaluate taxonomy and evolutionary
distances among organisms, with limited statistical confidence. The
study of fossils, on the other hand, can more specifically pinpoint
when and in what organism a mutation first appeared.
paleontology work together in the clarification of science's still dim
view of the appearance of life and its evolution.
Phacopid trilobite Eldredgeops rana crassituberculata, the genus is
named after Niles Eldredge
Crinoid columnals (Isocrinus nicoleti) from the Middle
Formation at Mount Carmel Junction, Utah
Niles Eldredge's study of the
Phacops trilobite genus supported the
hypothesis that modifications to the arrangement of the trilobite's
eye lenses proceeded by fits and starts over millions of years during
the Devonian. Eldredge's interpretation of the
record was that the aftermaths of the lens changes, but not the
rapidly occurring evolutionary process, were fossilized. This and
other data led
Stephen Jay Gould
Stephen Jay Gould and
Niles Eldredge to publish their
seminal paper on punctuated equilibrium in 1971.
X-ray tomographic analysis of early
embryonic microfossils yielded new insights of metazoan evolution at
its earliest stages. The tomography technique provides previously
unattainable three-dimensional resolution at the limits of
Fossils of two enigmatic bilaterians, the worm-like
Markuelia and a putative, primitive protostome, Pseudooides, provide a
peek at germ layer embryonic development. These 543-million-year-old
embryos support the emergence of some aspects of arthropod development
earlier than previously thought in the late Proterozoic. The preserved
Siberia underwent rapid diagenetic
phosphatization resulting in exquisite preservation, including cell
structures. This research is a notable example of how knowledge
encoded by the fossil record continues to contribute otherwise
unattainable information on the emergence and development of life on
Earth. For example, the research suggests
Markuelia has closest
affinity to priapulid worms, and is adjacent to the evolutionary
branching of Priapulida, Nematoda and Arthropoda.
Trading and collecting
Fossil trading and
Fossil trading is the practice of buying and selling fossils. This is
many times done illegally with artifacts stolen from research sites,
costing many important scientific specimens each year. The problem
is quite pronounced in China, where many specimens have been
Fossil collecting (some times, in a non-scientific sense, fossil
hunting) is the collection of fossils for scientific study, hobby, or
Fossil collecting, as practiced by amateurs, is the
predecessor of modern paleontology and many still collect fossils and
study fossils as amateurs. Professionals and amateurs alike collect
fossils for their scientific value.
Three small ammonite fossils, each approximately 1.5 cm across
Eocene fossil fish Priscacara liops from the Green
River Formation of
A permineralized trilobite, Asaphus kowalewskii
Carcharodontosaurus teeth. The latter was found in the
Fossil shrimp (Cretaceous)
Petrified cone of
Araucaria mirabilis from Patagonia,
Jurassic Period (approx. 210 Ma)
A fossil gastropod from the
Pliocene of Cyprus. A serpulid worm is
Eocene fossil flower, collected August 2010 from Clare family fossil
quarry, Florissant, Colorado
A fairy loaf fossil, which is one of the most found fossils in the UK
Productid brachiopod ventral valve; Roadian, Guadalupian (Middle
Permian); Glass Mountains, Texas.
Agatized coral from the
Hawthorn Group (Oligocene–Miocene), Florida.
An example of preservation by replacement.
Fossils from beaches of the
Baltic Sea island of Gotland, placed on
paper with 7 mm (0.28 inch) squares.
List of molluscan genera represented in the fossil record
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It's extremely hard to become a fossil, by Olivia Judson, The New York
Bones Are Not the Only Fossils, by Olivia Judson, The New York Times
The Wikibook Historical
Geology has a page on the topic of: Fossils
The Wikibook Historical
Geology has a page on the topic of: Fossils
and absolute dating
Wikiquote has quotations related to: Fossil
Look up fossil in Wiktionary, the free dictionary.
Wikimedia Commons has media related to fossils.
Fossils on In Our Time at the BBC.
Fossil Museum throughout Time and Evolution
Paleoportal, geology and fossils of the United States
Fossil Record, a complete listing of the families, orders, class
and phyla found in the fossil record
Paleontology at Curlie (based on DMOZ)
Ernest Ingersoll (1920). "Fossils". Encyclopedia
"Fossil". New International Encyclopedia. 1905.
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