Editing Taphonomy (section)

==Taphonomic biases in the fossil record==
{{more citations needed section|date=April 2011}}
Because of the very select processes that cause preservation, not all organisms have the same chance of being preserved. Any factor that affects the likelihood that an organism is preserved as a fossil is a potential source of bias. It is thus arguably the most important goal of taphonomy to identify the scope of such biases such that they can be quantified to allow correct interpretations of the relative abundances of organisms that make up a fossil biota.<ref>{{cite book |pages=290–336 |last1=Kidwell |first1=Susan M. |first2=Patrick J |last2=Brenchley |chapter=Evolution of the fossil record: thickness trends in marine skeletal accumulations and their implication |title= Evolutionary Paleobiology: In Honor of James W. Valentine |year=1996 |publisher=University of Chicago Press |isbn=9780226389110 |chapter-url=https://books.google.com/books?id=rfuDnYKBA7MC&pg=PA290 }}</ref> Some of the most common sources of bias are listed below.

===Physical attributes of the organism itself===
This perhaps represents the biggest source of bias in the fossil record. First and foremost, organisms that [[biomineralization|contain hard parts]] have a far greater chance of being represented in the fossil record than organisms consisting of soft tissue only. As a result, animals with bones or shells are overrepresented in the fossil record, and many plants are only represented by [[pollen]] or [[spore]]s that have hard walls. Soft-bodied organisms may form 30% to 100% of the biota, but most fossil assemblages preserve none of this unseen diversity, which may exclude groups such as [[fungi]] and entire animal [[phylum|phyla]] from the fossil record. Many animals that [[moult]], on the other hand, are overrepresented, as one animal may leave multiple fossils due to its discarded body parts. Among plants, [[Anemophily|wind-pollinated]] species produce so much more pollen than [[Zoophily|animal-pollinated]] species, the former being overrepresented relative to the latter.{{citation needed|date=April 2021}}

===Characteristics of the habitat===
Most fossils form in conditions where material is [[Deposition (geology)|deposit]]ed on the bottom of water bodies. Coastal areas are often prone to high rates of erosion, and rivers flowing into the sea may carry a high particulate load from inland. These sediments will eventually settle out, so organisms living in such environments have a much higher chance of being preserved as fossils after death than do those organisms living in non-depositing conditions. In continental environments, fossilization is likely in lakes and riverbeds that gradually fill in with organic and inorganic material. The organisms of such habitats are also liable to be overrepresented in the fossil record than those living far from these aquatic environments where burial by sediments is unlikely to occur.<ref>{{cite web |title=How are dinosaur fossils formed? |url=https://www.nhm.ac.uk/discover/how-are-fossils-formed.html |website=www.nhm.ac.uk |access-date=19 February 2022 |language=en}}</ref>

===Mixing of fossils from different places===
A [[sedimentology|sedimentary]] deposit may have experienced a mixing of noncontemporaneous remains within single sedimentary units via physical or biological processes; i.e. a deposit could be ripped up and redeposited elsewhere, meaning that a deposit may contain a large number of fossils from another place (an '''allochthonous''' deposit, as opposed to the usual '''autochthonous'''). Thus, a question that is often asked of fossil deposits is to what extent does the fossil deposit record the true biota that originally lived there? Many fossils are obviously autochthonous, such as rooted fossils like [[crinoid]]s,{{clarify|reason=all crinoids are "obviously" autochthonous? Meaning they were never moved by geologic processes? THIS IS NOT OBVIOUS, is it even true at all?|date=August 2018}} and many fossils are intrinsically obviously allochthonous, such as the presence of photoautotrophic plankton in a benthic deposit that must have sunk to be deposited. A fossil deposit may thus become biased towards exotic species (i.e. species not endemic to that area) when the sedimentology is dominated by gravity-driven surges, such as mudslides, or may become biased if there are very few endemic organisms to be preserved. This is a particular problem in [[palynology]].{{citation needed|date=April 2021}}

===Temporal resolution===
Because population turnover rates of individual taxa are much less than net rates of sediment accumulation, the biological remains of successive, noncontemporaneous populations of organisms may be admixed within a single bed, known as '''time-averaging'''. Because of the slow and episodic nature of the geologic record, two apparently contemporaneous fossils may have actually lived centuries, or even millennia, apart. Moreover, the ''degree'' of time-averaging in an assemblage may vary. The degree varies on many factors, such as tissue type, the habitat, the frequency of burial events and [[exhumation]] events, and the depth of [[bioturbation]] within the sedimentary column relative to net sediment accumulation rates. Like biases in spatial fidelity, there is a bias towards organisms that can survive reworking events, such as [[Exoskeleton|shell]]s. An example of a more ideal deposit with respect to time-averaging bias would be a [[volcanic ash]] deposit, which captures an entire biota caught in the wrong place at the wrong time (e.g. the [[Silurian]] [[Coalbrookdale Formation|Herefordshire lagerstätte]]).

===Gaps in time series===
The geological record is very discontinuous, and deposition is episodic at all scales. At the largest scale, a sedimentological high-stand period may mean that no deposition may occur for millions of years and, in fact, erosion of the deposit may occur. Such a hiatus is called an [[unconformity]]. Conversely, a catastrophic event such as a mudslide may overrepresent a time period. At a shorter scale, scouring processes such as the formation of ripples and dunes and the passing of [[turbidity current]]s may cause layers to be removed. Thus the fossil record is biased towards periods of greatest sedimentation; periods of time that have less sedimentation are consequently less well represented in the fossil record.{{citation needed|date=April 2021}}

A related problem is the slow changes that occur in the depositional environment of an area; a deposit may experience periods of poor preservation due to, for example, a lack of biomineralizing elements. This causes the taphonomic or diagenetic obliteration of fossils, producing gaps and condensation of the record.{{citation needed|date=April 2021}}

===Consistency in preservation over geologic time===

Major shifts in intrinsic and extrinsic properties of organisms, including morphology and behaviour in relation to other organisms or shifts in the global environment, can cause secular or long-term cyclic changes in preservation ([[megabias]]).{{citation needed|date=April 2021}}

===Human biases===
Much of the incompleteness of the fossil record is due to the fact that only a small amount of rock is ever exposed at the surface of the Earth, and not even most of that has been explored. Our fossil record relies on the small amount of exploration that has been done on this. Unfortunately, paleontologists as humans can be very biased in their methods of collection; a bias that must be identified. Potential sources of bias include,
*'''Search images''': field experiments have shown that paleontologists working on, say fossil clams are better at collecting clams than anything else because their search image has been shaped to bias them in favour of clams.
*'''Relative ease of extraction''': fossils that are easy to obtain (such as many phosphatic fossils that are easily extracted ''en masse'' by dissolution in acid) are overabundant in the fossil record.
*'''Taxonomic bias''': fossils with easily discernible morphologies will be easy to distinguish as separate species, and will thus have an inflated abundance.{{citation needed|date=April 2021}}