Editing Taphonomy (section)

==Preservation of biopolymers==
{{main|Preservation of biopolymers}}
[[File:ElrathiakingiUtahWheelerCambrian.jpg|thumb|Although [[chitin]] exoskeletons of arthropods such as insects and myriapods (but not [[trilobite]]s, which are mineralized with calcium carbonate, nor crustaceans, which are often mineralized with calcium phosphate) are subject to decomposition, they often maintain shape during [[permineralization]], especially if they are already somewhat mineralized.]]
[[File:Lizard-Green River Fm.jpg|thumb|Soft-bodied preservation of a lizard, Parachute Creek Member, Green River Formation, Utah. Most of the skeleton decalcified.]]
The taphonomic pathways involved in relatively inert substances such as calcite (and to a lesser extent bone) are relatively obvious, as such body parts are stable and change little through time.  However, the preservation of "soft tissue" is more interesting, as it requires more peculiar conditions. While usually only biomineralised material survives fossilisation, the preservation of soft tissue is not as rare as sometimes thought.<ref name=Briggs1993>{{cite journal |last1=Briggs |first1=Derek E. G. |last2=Kear |first2=Amanda J. |title=Decay and preservation of polychaetes: taphonomic thresholds in soft-bodied organisms |journal=Paleobiology |date=1993 |volume=19 |issue=1 |pages=107–135 |doi=10.1017/S0094837300012343 |bibcode=1993Pbio...19..107B |s2cid=84073818 }}</ref>

Both DNA and proteins are unstable, and rarely survive more than hundreds of thousands of years before degrading.<ref name=Anderson2023>{{cite journal |last1=Anderson |first1=L. A. |title=A chemical framework for the preservation of fossil vertebrate cells and soft tissues |journal=Earth-Science Reviews |date=May 2023 |volume=240 |pages=104367 |doi=10.1016/j.earscirev.2023.104367 |bibcode=2023ESRv..24004367A |s2cid=257326012 |doi-access=free }}</ref> Polysaccharides also have low preservation potential, unless they are highly cross-linked; this interconnection is most common in structural tissues, and renders them resistant to chemical decay.<ref name=Briggs1999>{{cite journal |last1=Jones |first1=M. K. |last2=Briggs |first2=D. E. G. |last3=Eglington |first3=G. |last4=Hagelberg |first4=E. |last5=Briggs |first5=Derek E. G. |title=Molecular taphonomy of animal and plant cuticles: selective preservation and diagenesis |journal=Philosophical Transactions of the Royal Society of London. Series B: Biological Sciences |date=29 January 1999 |volume=354 |issue=1379 |pages=7–17 |doi=10.1098/rstb.1999.0356 |pmc=1692454 }}</ref> Such tissues  include wood ([[lignin]]), spores and pollen ([[sporopollenin]]), the cuticles of plants ([[Cutan (polymer)|cutan]]) and animals, the cell walls of algae ([[algaenan]]),<ref name=Briggs1999/> and potentially the polysaccharide layer of some [[lichens]].{{Citation needed|date=January 2017}} This interconnectedness makes the chemicals less prone to chemical decay, and also means they are a poorer source of energy so less likely to be digested by scavenging organisms.<ref name=Anderson2023/> After being subjected to heat and pressure, these cross-linked organic molecules typically "cook" and become [[kerogen]] or short (<17 C atoms) aliphatic/aromatic carbon molecules.<ref name=Anderson2023/> Other factors affect the likelihood of preservation; for instance [[sclerotization]] renders the jaws of [[polychaete]]s more readily preserved than the chemically equivalent but non-sclerotized body cuticle.<ref name=Briggs1999/> A peer-reviewed study in 2023 was the first to present an in-depth chemical description of how biological tissues and cells potentially preserve into the fossil record. This study generalized the chemistry underlying cell and tissue preservation to explain the phenomenon for potentially any cellular organism.<ref name=Anderson2023/>

It was thought that only tough, cuticle type soft tissue could be preserved by [[Burgess Shale type preservation]],<ref name=Butterfield1990>{{cite journal |last1=Butterfield |first1=Nicholas J. |title=Organic preservation of non-mineralizing organisms and the taphonomy of the Burgess Shale |journal=Paleobiology |date=1990 |volume=16 |issue=3 |pages=272–286 |doi=10.1017/S0094837300009994 |jstor=2400788 |bibcode=1990Pbio...16..272B |s2cid=133486523 }}</ref> but an increasing number of organisms are being discovered that lack such cuticle, such as the probable chordate ''[[Pikaia]]'' and the shellless ''[[Odontogriphus]]''.<ref name=SCM2008>{{cite journal |last1=Morris |first1=Simon Conway |title=A redescription of a rare chordate, Metaspriggina Walcotti Simonetta and Insom, from the Burgess Shale (Middle Cambrian), British Columbia, Canada |journal=Journal of Paleontology |date=March 2008 |volume=82 |issue=2 |pages=424–430 |doi=10.1666/06-130.1 |bibcode=2008JPal...82..424M |s2cid=85619898 }}</ref>

It is a common misconception that anaerobic conditions are necessary for the preservation of soft tissue; indeed much decay is mediated by sulfate reducing bacteria which can only survive in anaerobic conditions.<ref name=Briggs1999/>  Anoxia does, however, reduce the probability that scavengers will disturb the dead organism, and the activity of other organisms is undoubtedly one of the leading causes of soft-tissue destruction.<ref name=Briggs1999/>

Plant cuticle is more prone to preservation if it contains [[Cutan (polymer)|cutan]], rather than [[cutin]].<ref name=Briggs1999/>

Plants and algae produce the most preservable compounds, which are listed according to their preservation potential by Tegellaar (see reference).<ref name=Tegelaar1989>{{cite journal |last1=Tegelaar |first1=E.W |last2=de Leeuw |first2=J.W |last3=Derenne |first3=S |last4=Largeau |first4=C |title=A reappraisal of kerogen formation |journal=Geochimica et Cosmochimica Acta |date=November 1989 |volume=53 |issue=11 |pages=3103–3106 |doi=10.1016/0016-7037(89)90191-9 |bibcode=1989GeCoA..53.3103T }}</ref>