Editing Fossil (section)

=== 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.<ref name=Smith>{{cite journal |url= http://www.smithsonianmag.com/science-nature/dinosaur-shocker-115306469/?no-ist |author=Fields H |title=Dinosaur Shocker – Probing a 68-million-year-old T. rex, Mary Schweitzer stumbled upon astonishing signs of life that may radically change our view of the ancient beasts |journal=Smithsonian Magazine |date= May 2006 |archive-url= https://web.archive.org/web/20150118153415/http://www.smithsonianmag.com/science-nature/dinosaur-shocker-115306469/?no-ist |url-status=live |archive-date= 18 January 2015}}</ref><ref name=MHS1>{{cite journal |vauthors=Schweitzer MH, Wittmeyer JL, Horner JR, Toporski JK |title= Soft-tissue vessels and cellular preservation in Tyrannosaurus rex |journal= Science |volume=307 |issue=5717 |pages=1952–5 |date= 25 March 2005 |pmid=15790853 |doi= 10.1126/science.1108397 |bibcode=2005Sci...307.1952S |s2cid= 30456613 }}</ref><ref name=MHS2>{{cite journal |vauthors=Schweitzer MH, Zheng W, Cleland TP, Bern M |title=Molecular analyses of dinosaur osteocytes support the presence of endogenous molecules |journal=Bone |volume=52 |issue=1 |pages=414–23 |date=January 2013 |pmid=23085295 |doi= 10.1016/j.bone.2012.10.010}}</ref><ref name=Emb>{{cite journal | url= https://www.researchgate.net/publication/10586201 |vauthors=Embery G, Milner AC, Waddington RJ, Hall RC, Langley ML, Milan AM |title=Identification of Proteinaceous Material in the Bone of the Dinosaur Iguanodon |journal=Connective Tissue Research |volume=44 |pages=41–6 |date=2003 |pmid=12952172 | doi= 10.1080/03008200390152070 |issue=Suppl 1|s2cid=2249126 }}</ref> In 2014, [[Mary Higby Schweitzer|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.<ref name= SchweitzerOthers2014a>{{cite journal |vauthors=Schweitzer MH, Zheng W, Cleland TP, Goodwin MB, Boatman E, Theil E, Marcus MA, Fakra SC | title= A role for iron and oxygen chemistry in preserving soft tissues, cells and molecules from deep time |journal= Proceedings of the Royal Society | volume= 281 |issue= 1774 |date= Nov 2013 |pmid= 24285202 |pmc= 3866414 | doi= 10.1098/rspb.2013.2741 | page=20132741}}</ref> 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.<ref name=ZL11>{{cite journal| last1=Zylberberg |first1=L. | last2=Laurin|first2=M.|year=2011 |title=Analysis of fossil bone organic matrix by transmission electron microscopy |journal=Comptes Rendus Palevol |volume=11 |issue=5–6 |pages=357–366 | doi = 10.1016/j.crpv.2011.04.004}}</ref> There seemed to be no correlation between geological age and quality of preservation, within that timeframe.