2.1 Biostratinomy

Biostratinomy examines how organisms change after death but before burial. It looks at decay, disarticulation, transport, and burial processes that affect fossil preservation. Understanding these factors helps paleontologists interpret the fossil record accurately.

Decay rates, disarticulation, and transport all influence how fossils form. Rapid burial often leads to better preservation. Time-averaging and faunal mixing can create biases in fossil assemblages, impacting our understanding of past ecosystems.

Biostratinomy definition and scope

• Biostratinomy is the study of the processes that affect organic remains from the time of death until the time of burial
• Focuses on the physical and chemical changes that occur to organisms after death and before final burial in sediment
• Includes processes such as decay, disarticulation, transport, and burial which can significantly influence the preservation and distribution of fossils

Necrolysis and decay

Autolysis vs heterolysis

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• Autolysis is the self-digestion of cells by their own enzymes after death
• Heterolysis involves the breakdown of organic matter by external decomposers such as bacteria and fungi
• Autolysis typically occurs first and is followed by heterolysis in the decay process

Aerobic vs anaerobic decay

• Aerobic decay occurs in the presence of oxygen and is usually faster and more complete
• Anaerobic decay takes place in the absence of oxygen and is slower, often resulting in the preservation of more organic material
• The type of decay can greatly influence the preservation potential of organic remains

Factors affecting decay rates

• Temperature higher temperatures accelerate decay while lower temperatures slow it down
• Moisture decay is faster in moist environments compared to dry conditions
• Oxygen availability aerobic environments promote faster decay than anaerobic settings
• Biological factors such as the presence of scavengers or decomposers can also affect decay rates

Disarticulation and dissociation

Connective tissue decomposition

• Disarticulation is the separation of skeletal elements at their joints due to the decomposition of connective tissues (ligaments, tendons)
• The rate of connective tissue decay depends on factors such as temperature, moisture, and bacterial activity
• Different types of connective tissues have varying decay rates, leading to a predictable sequence of disarticulation

Scavenging and bioturbation effects

• Scavengers can disarticulate and scatter skeletal elements while feeding on soft tissues
• Bioturbation by burrowing organisms can also contribute to the disarticulation and dissociation of skeletal elements
• The activity of scavengers and bioturbators can significantly alter the spatial distribution of fossil remains

Transport-induced disarticulation

• Moving water or wind can cause physical disarticulation of skeletal elements
• Transport can also lead to the sorting and differential dispersal of skeletal elements based on their size, shape, and density
• The degree of transport-induced disarticulation depends on the energy and duration of the transport process

Reorientation and transport

Skeletal element dispersal

• After disarticulation, skeletal elements can be dispersed by various transport processes
• Dispersal can occur in both terrestrial (wind, water) and aquatic (currents, waves) environments
• The extent of dispersal depends on the transport medium, energy, and duration, as well as the properties of the skeletal elements

Hydraulic equivalence concept

• Hydraulic equivalence refers to the idea that particles of different sizes, shapes, and densities can be transported together under similar flow conditions
• This concept is important for understanding the sorting and distribution of skeletal elements in aquatic environments
• Hydraulically equivalent elements may be deposited together, even if they originate from different organisms or body parts

Transport in terrestrial environments

• In terrestrial settings, transport can occur through wind (aeolian) or water (fluvial) processes
• Wind transport is more selective and can result in the sorting of lighter and more aerodynamic elements
• Fluvial transport can lead to the dispersal and accumulation of skeletal elements in channels, floodplains, and alluvial fans

Transport in aquatic environments

• Aquatic transport can occur in both marine and freshwater settings
• Currents, waves, and tides are the main agents of transport in aquatic environments
• The transport and deposition of skeletal elements in aquatic settings are influenced by factors such as water depth, energy, and bottom topography

Burial and sedimentation

Rapid burial and exceptional preservation

• Rapid burial is essential for the exceptional preservation of fossils, as it minimizes the time available for decay and disarticulation
• Rapid burial can occur through various mechanisms, such as sediment gravity flows (turbidites), volcanic ash falls, and sudden flooding events
• Exceptionally preserved fossils (Lagerstätten) often result from rapid burial, which can preserve soft tissues, color patterns, and even behavior

Obrution vs stagnation deposits

• Obrution deposits form when organisms are rapidly buried alive by sediment, often leading to exceptional preservation
• Stagnation deposits occur in low-energy, oxygen-depleted environments where burial is gradual, and decay is slowed down
• The type of deposit can influence the quality and completeness of fossil preservation

Sedimentation rates and fossil preservation

• Sedimentation rate plays a crucial role in fossil preservation
• High sedimentation rates favor the rapid burial and preservation of fossils
• Low sedimentation rates increase the time available for decay, disarticulation, and transport, potentially leading to lower-quality preservation

Time-averaging and faunal mixing

Within-habitat time-averaging

• Time-averaging occurs when fossils from different time intervals are mixed within a single sedimentary layer
• Within-habitat time-averaging involves the mixing of fossils from the same habitat but different time periods
• This can lead to the overestimation of species richness and the underestimation of species turnover rates

Between-habitat mixing

• Between-habitat mixing occurs when fossils from different habitats are transported and deposited together
• This can happen due to processes such as storm events, tsunamis, or large-scale transport
• Between-habitat mixing can create fossil assemblages that do not accurately reflect the original living communities

Stratigraphic resolution and time-averaging

• Stratigraphic resolution refers to the ability to distinguish between different time intervals within a sedimentary sequence
• High stratigraphic resolution reduces the degree of time-averaging and allows for a more accurate reconstruction of past communities and environments
• Low stratigraphic resolution increases the likelihood of time-averaging and can limit the temporal precision of paleoecological interpretations

Biostratinomy in different environments

Terrestrial biostratinomy

• Terrestrial biostratinomy deals with the processes affecting organic remains in land-based environments
• Key factors include weathering, erosion, transport by wind or water, and burial in soils or sediments
• Examples of terrestrial biostratinomy include the preservation of vertebrate remains in fluvial or aeolian deposits and the formation of dinosaur bonebeds

Shallow marine biostratinomy

• Shallow marine biostratinomy focuses on the processes occurring in coastal and shelf environments
• Factors such as waves, tides, storms, and bioturbation play a significant role in the distribution and preservation of marine fossils
• Examples include the formation of shell beds, the preservation of reef communities, and the accumulation of marine vertebrate remains

Deep marine biostratinomy

• Deep marine biostratinomy deals with the processes affecting organic remains in deep ocean settings
• Low sedimentation rates, oxygenation levels, and the influence of deep-sea currents are important factors
• Examples include the preservation of marine microorganisms in deep-sea sediments and the formation of fossil assemblages associated with submarine canyons or deep-water reefs

Biostratinomy and fossil preservation

Biostratinomy's influence on fossil record

• Biostratinomic processes play a crucial role in determining which organisms are preserved as fossils and how they are preserved
• Factors such as decay, disarticulation, transport, and burial can lead to biases in the fossil record
• Understanding biostratinomy helps paleontologists interpret the limitations and potential biases in the fossil record

Biases in fossil assemblages

• Fossil assemblages can be biased due to differential preservation potential among organisms
• Hard-bodied organisms (shells, bones) are more likely to be preserved than soft-bodied ones
• Transport processes can lead to the over-representation of certain skeletal elements or size classes in fossil assemblages

Implications for paleoecological interpretations

• Biostratinomic biases can affect paleoecological interpretations based on fossil assemblages
• Time-averaging and faunal mixing can lead to the overestimation of species richness and the misinterpretation of community structure
• Recognizing and accounting for biostratinomic processes is essential for accurate paleoecological reconstructions and interpretations of past ecosystems