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A compression fossil is a
fossil A fossil (from Classical Latin , ) 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, objects preserved ...
preserved in
sedimentary rock Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earth's surface, followed by cementation. Sedimentation is the collective name for processes that cause these particles ...
that has undergone physical compression. While it is uncommon to find
animal Animals are multicellular, eukaryotic organisms in the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, are able to move, can reproduce sexually, and go through an ontogenetic stage ...
s preserved as good compression fossils, it is very common to find
plant Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae ex ...
s preserved this way. The reason for this is that physical compression of the rock often leads to
distortion In signal processing, distortion is the alteration of the original shape (or other characteristic) of a signal. In communications and electronics it means the alteration of the waveform of an information-bearing signal, such as an audio sig ...
of the fossil. The best fossils of
leaves A leaf ( : leaves) is any of the principal appendages of a vascular plant stem, usually borne laterally aboveground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", while the leaves, ste ...
are found preserved in fine layers of
sediment Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, san ...
that have been compressed in a direction
perpendicular In elementary geometry, two geometric objects are perpendicular if they intersect at a right angle (90 degrees or π/2 radians). The condition of perpendicularity may be represented graphically using the ''perpendicular symbol'', ⟂. It can ...
to the plane of the deposited sediment. Since leaves are basically flat, the resulting distortion is minimal.
Plant stem A stem is one of two main structural axes of a vascular plant, the other being the root. It supports leaves, flowers and fruits, transports water and dissolved substances between the roots and the shoots in the xylem and phloem, stores nutrie ...
s and other three-dimensional plant structures do not preserve as well under compression. Typically, only the basic outline and surface features are preserved in compression fossils; internal
anatomy Anatomy () is the branch of biology concerned with the study of the structure of organisms and their parts. Anatomy is a branch of natural science that deals with the structural organization of living things. It is an old science, having its ...
is not preserved. These fossils may be studied while still partially entombed in the sedimentary rock matrix where they are preserved, or once lifted out of the matrix by a peel or transfer technique. Compression fossils are formed most commonly in environments where fine sediment is deposited, such as in
river delta A river delta is a landform shaped like a triangle, created by deposition of sediment that is carried by a river and enters slower-moving or stagnant water. This occurs where a river enters an ocean, sea, estuary, lake, reservoir, or (more ...
s,
lagoon A lagoon is a shallow body of water separated from a larger body of water by a narrow landform, such as reefs, barrier islands, barrier peninsulas, or isthmuses. Lagoons are commonly divided into ''coastal lagoons'' (or ''barrier lagoons'' ...
s, along
river A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases, a river flows into the ground and becomes dry at the end of its course without reaching another body of ...
s, and in
pond A pond is an area filled with water, either natural or Artificiality, artificial, that is smaller than a lake. Defining them to be less than in area, less than deep, and with less than 30% Aquatic plant, emergent vegetation helps in disting ...
s. The best rocks in which to find these fossils preserved are
clay Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4). Clays develop plasticity when wet, due to a molecular film of water surrounding the clay parti ...
and
shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4) and tiny fragments ( silt-sized particles) of other minerals, especial ...
, although
volcanic ash Volcanic ash consists of fragments of rock, mineral crystals, and volcanic glass, created during volcanic eruptions and measuring less than 2 mm (0.079 inches) in diameter. The term volcanic ash is also often loosely used to refer ...
may sometimes preserve plant fossils as well.


Slabs

A slab and counter slab, more often called a part and counterpart in paleoentomology and paleobotany, are the matching halves of a compression fossil, a fossil-bearing
matrix Matrix most commonly refers to: * ''The Matrix'' (franchise), an American media franchise ** ''The Matrix'', a 1999 science-fiction action film ** "The Matrix", a fictional setting, a virtual reality environment, within ''The Matrix'' (franchis ...
formed in
sedimentary Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earth's surface, followed by cementation. Sedimentation is the collective name for processes that cause these particles ...
deposits. When excavated the matrix may be split along the natural grain or cleavage of the rock. A fossil embedded in the sediment may then also split down the middle, with fossil remains sticking to both surfaces, or the counter slab may simply show a negative impression or mould of the fossil. Comparing slab and counter slab has led to the exposure of a number of fossil forgeries. Differences between the impressions on slab and counterslab led astronomer
Fred Hoyle Sir Fred Hoyle FRS (24 June 1915 – 20 August 2001) was an English astronomer who formulated the theory of stellar nucleosynthesis and was one of the authors of the influential B2FH paper. He also held controversial stances on other sc ...
and applied physicist Lee Spetner in 1985 to declare that some ''
Archaeopteryx ''Archaeopteryx'' (; ), sometimes referred to by its German name, "" ( ''Primeval Bird''), is a genus of bird-like dinosaurs. The name derives from the ancient Greek (''archaīos''), meaning "ancient", and (''ptéryx''), meaning "feather" ...
'' fossils had been forged, a claim dismissed by most palaeontologists. In its November 1999 edition, ''
National Geographic ''National Geographic'' (formerly the ''National Geographic Magazine'', sometimes branded as NAT GEO) is a popular American monthly magazine published by National Geographic Partners. Known for its photojournalism, it is one of the most widely ...
'' magazine announced the discovery of '' Archaeoraptor'', a link between dinosaurs and birds, from a 125 million-year-old fossil that had come from
Liaoning Province Liaoning () is a coastal province in Northeast China that is the smallest, southernmost, and most populous province in the region. With its capital at Shenyang, it is located on the northern shore of the Yellow Sea, and is the northernmost ...
of China. Chinese palaeontologist Xu Xing came into possession of the counter slab through a fossil hunter. On comparing his fossil with images of ''Archaeoraptor'' it became evident that it was a composite fake. His note to ''National Geographic'' led to consternation and embarrassment. Lewis Simons investigated the matter on behalf of ''National Geographic''. In October 2000, he reported what he termed: It was eventually determined that ''Archaeoraptor'' had been constructed from parts of an
Early Cretaceous The Early Cretaceous ( geochronological name) or the Lower Cretaceous ( chronostratigraphic name), is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 145  Ma to 100.5 Ma. Geology Pr ...
bird '' Yanornis martini'' and a small dinosaur ''
Microraptor zhaoianus ''Microraptor'' (Greek, μικρός, ''mīkros'': "small"; Latin, ''raptor'': "one who seizes") is a genus of small, four-winged dromaeosaurid dinosaurs. Numerous well-preserved fossil specimens have been recovered from Liaoning, China. They ...
''. In order to increase their profit, fossil hunters and dealers occasionally sell slab and counter slab separately. A reptile fossil also found in Liaoning was described and named ''Sinohydrosaurus'' in 1999 by the Beijing Natural History Museum. In the same year the
Institute of Vertebrate Paleontology and Paleoanthropology The Institute of Vertebrate Paleontology and Paleoanthropology (IVPP; ) of China is a research institution and collections repository for fossils, including many dinosaur and pterosaur specimens (many from the Yixian Formation). As its name suggest ...
in Beijing described and named ''Hyphalosaurus lingyuanensis'', unaware they were working with the counter slab of the same specimen. '' Hyphalosaurus'' is now the accepted name.Two Guys Fossils


References

{{Reflist, 2, refs= {{cite book , last=Arnold , first=Chester A. , year=1947 , title=An Introduction to Paleobotany , url=https://archive.org/details/in.ernet.dli.2015.270777 , edition=1st , location=New York & London , publisher=McGraw-Hill Book Company , page
14
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{{cite book , last1=Stewart , first1=Wilson N. , last2=Rothwell , first2=Gar W. , year=1993 , title=Paleobotany and the Evolution of Plants , edition=2nd , location=Cambridge , publisher=Cambridge University Press , isbn=0-521-38294-7 , pages=7–22 {{cite book , last1=Taylor , first1=Thomas N. , last2=Taylor , first2=Edith L. , year=1993 , title=The Biology and Evolution of Fossil Plants , location =Englewood Cliffs, NJ , publisher=Prentice Hall , isbn=0-13-651589-4 , pages=7–12 Fossilization