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Compression fossils are formed most commonly in [[ecosystem|environment]]s where fine sediment is deposited, such as in [[river delta]]s, [[lagoon]]s, along [[river]]s, and in [[pond]]s. The best rocks in which to find these fossils preserved are [[clay]] and [[shale]], although [[volcanic ash]] may sometimes preserve plant fossils as well.<ref name="Taylor & Taylor 1993"/>
==Slabs==
[[File:Pterodactylus antiquus p and cp.jpg|thumb|Counter slab (left) and slab (right) of ''[[Pterodactylus]]'']]
A slab and counter slab, more often called a part and counter part in paleoentomology<ref name="Jepson2011">{{cite journal |last1=Jepson |first1=J.E. |last2=Ansorge |first2=J. |last3=Jarzembowski |first3=E.A. |year=2011 |title=New snakeflies (Insecta: Raphidioptera) from the Lower Cretaceous of the UK, Spain and Brazil |journal= Palaeontology |volume=54 |issue=2 |pages=385–395 |doi=10.1111/j.1475-4983.2011.01038.x}}</ref> and paleobotany,<ref name="Channing2011">{{cite journal |last1=Channing |first1=A. |last2=Zamuner |first2=A. |last3=Edwards |first3=D. |last4=Guido |first4=D. |year=2011 |title=''Equisetum thermale'' sp. nov. (Equisetales) from the Jurassic San Agustin hot spring deposit, Patagonia: Anatomy, paleoecology, and inferred paleoecophysiology. |journal= American Journal of Botany |volume=98 |issue=4 |pages=680–697 |doi= 10.3732/ajb.1000211 |pmid=21613167}}</ref> are the matching halves of a compression fossil, a fossil-bearing [[Matrix (geology)|matrix]] formed in [[sedimentary]] 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.<ref>[http://www.proz.com/kudoz/english_to_polish/archaeology/762880-slab_counter_slab.html ProZ]</ref> 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 [[Fred Hoyle]] and [[Lee Spetner]] in 1985 to declare that some ''[[Archaeopteryx]]'' fossils had been [[Archaeopteryx#Controversy|forged]], a claim dismissed by most palaeontologists.<ref>[http://books.google.co.za/books?id=gWtV-9zG8ycC&pg=PA3&lpg=PA3&dq=fossil+%22Counter+slab%22&source=bl&ots=CA29NkZFrV&sig=3fBfq4s4V6-8EgE0Fs257BMoFDg&hl=en&ei=bd81TI6YN9PFsgaytY3OAQ&sa=X&oi=book_result&ct=result&resnum=9&ved=0CEAQ6AEwCA#v=onepage&q=fossil%20%22Counter%20slab%22&f=false New Scientist 14 March 1985]</ref>
In its November 1999 edition, ''[[National Geographic Magazine|National Geographic]]'' magazine announced the discovery of ''[[Archaeoraptor]]'', a link between dinosaurs and birds, from a 125 million year-old fossil that had come from the [[Liaoning Province]] of China. Chinese palaeontologist [[Xu Xing (paleontologist)|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. A certain Lewis Simons investigated the matter on behalf of National Geographic. In October 2000 he reported what he termed:
"''... a tale of misguided secrecy and misplaced confidence, of rampant egos clashing, self-aggrandizement, wishful thinking, naïve assumptions, human error, stubbornness, manipulation, backbiting, lying, corruption, and, most of all, abysmal communication. "''
It was eventually determined that ''Archaeoraptor'' had been constructed from parts of an [[Early Cretaceous]] bird ''[[Yanornis martini]]'' and a small dinosaur ''[[Microraptor zhaoianus]]''<ref>[http://www.ifs.csic.es/sorites/Issue_20/colbourn.htm The Interpretive Mind]</ref>
In order to increase their profit, fossil hunters and dealers occasionally sell slab and counter slab separately. A reptile fossil also found in Liaoning Province was described and named ''Sinohydrosaurus'' in 1999 by the [[Beijing Natural History Museum]]. In the same year the [[Institute of Vertebrate Paleontology and Paleoanthropology]] 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.<ref>[http://www.twoguysfossils.com/reptiles.htm Two Guys Fossils]</ref>
==References==
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