Taphonomy

Taphonomy is the study of how organisms decay and become fossilized or preserved in the paleontological record. The term taphonomy (from Greek táphos, τάφος 'burial' and nomos, νόμος 'law') 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 (living contexts), enter the lithosphere (buried contexts), 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:

Archaeobotany Archaeology Biology Forensic science Geoarchaeology Geology Paleoecology Paleontology Zooarchaeology 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 (i.e. floods, scavengers etc.). Accumulation occurs when there is a buildup of organic and/or inorganic materials in one location (scavengers or human behavior). 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 (i.e. freeze-thaw, compaction, transport, burial). 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 (vegetal or animal) 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 (plants, invertebrates, vertebrates). 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. (See § Temporal resolution below.) 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 (the study of trace fossils) 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.

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