Taphonomy


Taphonomy is the study of how organisms decay and become fossilized or preserved in the paleontological record. The term taphonomy was introduced to paleontology in 1940 by Soviet scientist Ivan Efremov to describe the study of the transition of remains, parts, or products of organisms from the biosphere to the lithosphere.
The term taphomorph is used to describe fossil structures that represent poorly-preserved, deteriorated remains of a mixture of taxonomic groups, rather than of a single one.

Description

Taphonomic phenomena are grouped into two phases: biostratinomy, events that occur between the death of the organism and the burial; and diagenesis, events that occur after the burial. Since Efremov's definition, taphonomy has expanded to include the fossilization of organic and inorganic materials through both cultural and environmental influences. Taphonomy is now most widely defined as the study of what happens to objects after they leave the biosphere, enter the lithosphere, and are subsequently recovered and studied.
This is a multidisciplinary concept that is used in slightly different contexts across various fields of study. Fields that employ the concept of taphonomy include:
There are five main stages of taphonomy: disarticulation, dispersal, accumulation, fossilization, and mechanical alteration. The first stage, disarticulation, occurs as the organism decays and the bones are no longer held together by the flesh and tendons of the organism. Dispersal is the separation of pieces of an organism caused by natural events. Accumulation occurs when there is a buildup of organic and/or inorganic materials in one location. When mineral-rich groundwater permeates organic materials and fills the empty spaces, a fossil is formed. The final stage of taphonomy is mechanical alteration; these are the processes that physically alter the remains. These stages are not only successive, they interplay. For example, chemical changes occur at every stage of the process due to the presence of bacteria. Changes begin as soon as the death of the organism: enzymes are released that destroy the organic contents of the tissues, and mineralised tissues such as bone, enamel and dentin are a mixture of organic and mineral components. Moreover, most often the organisms are dead because a predator has killed them. Digestion modifies the composition of the flesh, as well as that of the bones.

Research areas

Taphonomy has undergone an explosion of interest since the 1980s, with research focusing on certain areas.
  • Microbial, biogeochemical, and larger-scale controls on the preservation of different tissue types; in particular, exceptional preservation in Konzervat-lagerstätten. Covered within this field is the dominance of biological versus physical agents in the destruction of remains from all major taxonomic groups.
  • Processes that concentrate biological remains, especially the degree to which different types of assemblages reflect the species composition and abundance of source faunas and floras.
  • Actualistic taphonomy uses the present to understand past taphonomic events. This is often done through controlled experiments, such as the role microbes play in fossilization, the effects of mammalian carnivores on bone, or the burial of bone in a water flume. Computer modeling is also used to explain taphonomic events. Studies on actualistic taphonomy gave rise to the discipline conservation paleobiology.
  • The spatio-temporal resolution and ecological fidelity of species assemblages, particularly the relatively minor role of out-of-habitat transport contrasted with the major effects of time-averaging.
  • The outlines of megabiases in the fossil record, including the evolution of new bauplans and behavioral capabilities, and by broad-scale changes in climate, tectonics, and geochemistry of Earth surface systems.
  • The Mars Science Laboratory mission objectives evolved from assessment of ancient Mars habitability to developing predictive models on taphonomy.

    Paleontology

One motivation behind taphonomy is to understand biases present in the fossil record better. 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. For example, if a fossil assemblage contains more of one type of fossil than another, one can infer either that the organism was present in greater numbers or that its remains were more resistant to decomposition.
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, palaeontologists have been able to provide new and meaningful interpretations and correlations that would have otherwise remained obscure in the fossil record. In the marine environment, taphonomy, specifically aragonite loss, poses a major challenge in reconstructing past environments from the modern, notably in settings such as carbonate platforms.

Forensic science

Forensic taphonomy is a relatively new field that has gained popularity over the past 15 years. It is a subfield of forensic anthropology focusing specifically on how taphonomic forces have altered criminal evidence.
There are two different branches of forensic taphonomy: and . Biotaphonomy examines the process of decomposition and/or destruction of the organism. The main factors that affect this branch are categorised into three groups: environmental factors, external variables, individual factors, factors from the organism itself, and cultural factors, factors specific to any cultural behaviours that would affect the decomposition. Geotaphonomy studies how the burial practices and the burial itself affect the surrounding environment. This includes soil disturbances and tool marks from digging the grave, disruption of plant growth and soil pH from the decomposing body, and the alteration of the land and water drainage from introducing an unnatural mass to the area.
This field is essential because it helps scientists use the taphonomic profile to help determine what happened to the remains at the time of death and after death. This can make a huge difference when considering what can be used as evidence in a criminal investigation.

Archaeology

Taphonomy is a crucial study for archaeologists to better interpret archaeological sites. Since the archaeological record is often incomplete, taphonomy helps explain how it became incomplete. The methodology of taphonomy involves observing transformation processes to understand their impact on archaeological material and interpret patterns at real sites. This is mainly in the form of assessing how the deposition of the preserved remains of an organism has occurred to understand a deposit better.
Whether the deposition was a result of humans, animals and/or the environment is often the goal of taphonomic study. Archaeologists typically separate natural from cultural processes when identifying evidence of human interaction with faunal remains. This is done by looking at human processes preceding artifact discard in addition to processes after artifact discard. Changes preceding discard include butchering, skinning, and cooking. Understanding these processes can inform archaeologists on tool use or how an animal was processed. When the artifact is deposited, abiotic and biotic modifications occur. These can include thermal alteration, rodent disturbances, gnaw marks, and the effects of soil pH to name a few.
While taphonomic methodology can be applied and used to study a variety of materials such as buried ceramics and lithics, its primary application in archaeology involves the examination of organic residues. Interpretation of the post-mortem, pre-, and post-burial histories of faunal assemblages is critical in determining their association with hominid activity and behaviour.
For instance, to distinguish the bone assemblages that are produced by humans from those of non humans, much ethnoarchaeological observation has been done on different human groups and carnivores, to ascertain if there is anything different in the accumulation and fragmentation of bones. This study has also come in the form of excavation of animal dens and burrows to study the discarded bones and experimental breakage of bones with and without stone tools.
Studies of this kind by C.K. Brain in South Africa have shown that bone fractures previously attributed to "killer man-apes" were in fact caused by the pressure of overlying rocks and earth in limestone caves. His research has also demonstrated that early hominins, for example australopithecines, were more likely preyed upon by carnivores rather than being hunters themselves, from cave sites such as Swartkrans in South Africa.
Outside of Africa Lewis Binford observed the effects of wolves and dogs on bones in Alaska and the American Southwest, differentiating the interference of humans and carnivores on bone remains by the number of bone splinters and the number of intact articular ends. He observed that animals gnaw and attack the articular ends first leaving mostly bone cylinders behind, therefore it can be assumed a deposit with a high number of bone cylinders and a low number of bones with articular ends intact is therefore probably the result of carnivore activity. In practice John Speth applied these criteria to the bones from the Garnsey site in New Mexico. The rarity of bone cylinders indicated that there had been minimal destruction by scavengers, and that the bone assemblage could be assumed to be wholly the result of human activity, butchering the animals for meat and marrow extraction.
One of the most important elements in this methodology is replication, to confirm the validity of results.
There are limitations to this kind of taphonomic study in archaeological deposits as any analysis has to presume that processes in the past were the same as today, e.g that living carnivores behaved in a similar way to those in prehistoric times. There are wide variations among existing species so determining the behavioural patterns of extinct species is sometimes hard to justify. Moreover, the differences between faunal assemblages of animals and humans is not always so distinct, hyenas and humans display similar patterning in breakage and form similarly shaped fragments as the ways in which a bone can break are limited. Since large bones survive better than plants this also has created a bias and inclination towards big-game hunting rather than gathering when considering prehistoric economies.
While all of archaeology studies taphonomy to some extent, certain subfields deal with it more than others. These include zooarchaeology, geoarchaeology, and paleoethnobotany.