Taphonomy is the study of decaying organisms over time and how they become fossilized. The term taphonomy, was introduced to paleontology in 1940 by Russian scientist Ivan Efremov to describe the study of the transition of remains, parts, or products of organisms, from the biosphere, to the lithosphere, i.e. the creation of fossil assemblages.
Taphonomists study such phenomena as biostratinomy, decomposition, diagenesis, and encrustation and bioerosion by sclerobionts.
One motivation behind the study of taphonomy is to better understand biases present in the fossil record. Fossils are ubiquitous in sedimentary rocks, yet paleontologists cannot draw the most accurate conclusions about the lives and ecology of the fossilized organisms without knowing about the processes involved in their fossilization.
During the late twentieth century, taphonomic data began to be applied to other paleontological subfields such as paleobiology, paleoceanography, ichnology and biostratigraphy. By coming to understand the oceanographic and ethological implications of observed taphonomic patterns, paleontologists have been able to provide new and meaningful interpretations and correlations that would have otherwise remained obscure in the fossil record.
Archaeologists study taphonomic processes in order to determine how plant and animal remains accumulate and differentially preserve within archaeological sites. This is critical to determining whether these remains are associated with human activity. In addition, taphonomic processes may alter biological remains after they are deposited at a site. Some remains survive better than others over time, and can therefore bias an excavated collection.
Forensic taphonomy is concerned with the study of the decomposition of human remains, particularly in the context of burial sites.Experimental taphonomy testing usually consists of exposing the remains of organisms to various altering processes, and then examining the effects of the exposure.
Because of the very select processes that cause preservation, not all organisms have the same chance of being preserved. 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 biota.
A 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 an deposit may contain a large amount of fossils from another place.
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 crinoids, and many fossils are intrisically obviously allocthonous, 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 is very little endemic organisms to be preserved. This is a particular problem in palynology.
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 shells. 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.
This perhaps represents the biggest source of bias in the fossil record. First and foremost, biomineralizing organisms have a far greater chance of being represented in the fossil record than an entirely soft bodied organism.
We know from habitats around the world that soft bodied organisms may form 30% to 100% of the biota, however most fossil assembalges preserve none of this unseen diversity. This bias thus acts at a very great taxonomic level, with entire phyla of animals cut out of the fossil record due to a lack of hard parts. Many animals that moult, on the other hand, are overrepresented, as one animal may leave multiple fossils due to its discarded body parts.
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 tens of thousands 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 currents 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.
A related problem is the slow changes that occur in the depositional environment of an area; a deposit may experience periods of poor preservation to, for example, a lack of biomineralizing elements. This causes the taphonomic or diagenetic obliteration of fossils, producing gaps and condensation of the record.
Taphonomy has undergone an explosion of interest since the 1980s, with research focussing on certain areas.
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,