Date of issue: 25 March Description of the book "Vertebrate Taphonomy": Taphonomy studies the transition of organic matter from the biosphere into the geological record. It is particularly relevant to zooarchaeologists and paleobiologists, who analyse organic remains in the archaeological record in an attempt to reconstruct hominid subsistence patterns and paleoecological conditions. In this user-friendly, encyclopedic reference volume for students and professionals, R. Lee Lyman, a leading researcher in taphonomy, reviews the wide range of analytical techniques used to solve particular zooarchaeological problems, illustrating these in most cases with appropriate examples. He also covers the history of taphonomic research and its philosophical underpinnings.
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Learn how and when to remove this template message 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.
Physical attributes of the organism itself[ edit ] This perhaps represents the biggest source of bias in the fossil record. First and foremost, organisms that 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 spores that have hard walls. Among plants, wind-pollinated species produce so much more pollen than animal-pollinated species, that the former are much overrepresented relative to the latter.
Characteristics of the habitat[ edit ] Most fossils form in conditions where material is deposited to the bottom of water bodies. Especially shallow sea coasts produce large amounts of fossils, so organisms living in such conditions have a much higher chance of being preserved as fossils than organisms living in non-depositing conditions.
In continental environments, fossilization is especially likely in small lakes that gradually fill in with organic and inorganic material and especially in peat-accumulating wetlands.
The organisms of such habitats are therefore overrepresented in the fossil record. Mixing of fossils from different places[ edit ] A sedimentary deposit may have experienced a mixing of noncontemporaneous remains within single sedimentary units via physical or biological processes; i.
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,[ clarification needed ] 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.
This is a particular problem in palynology. Temporal resolution[ edit ] 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 e. Gaps in time series[ edit ] 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 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 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.
Consistency in preservation over geologic time[ edit ] Major shifts in intrinsic and extrinsic properties of organisms, including morphology and behavior in relation to other organisms or shifts in the global environment, can cause secular or long-term cyclic changes in preservation megabias.
Human biases[ edit ] 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. Preservation of biopolymers[ edit ] Main article: Preservation of biopolymers Although chitin exoskeletons of arthropods such as insects and myriapods but not trilobites , 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.
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. However, the dominant force actually seems to be predation, with scavengers more likely than rough waters to break up a fresh carcass before it is buried.
However, erosion also tends to destroy smaller fossils more easily. From the time of death or burial until excavation, taphonomy can aid in the understanding of past environments. Often these findings can be used to better understand cultural or environmental shifts within the present day.
Vertebrate Taphonomy by R. Lee Lyman (1994, Paperback)