2.1 Biostratinomy
6 min read•august 20, 2024
Biostratinomy examines how organisms change after death but before burial. It looks at decay, disarticulation, , 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 (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 and freshwater settings
- Currents, waves, and tides are the main agents of transport in aquatic environments
- The transport and 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
Key Terms to Review (18)
Biofacies: Biofacies refers to a specific assemblage of fossil organisms that reflect the ecological conditions of a particular environment at the time of deposition. This concept helps in understanding how different biological communities interact with their environments and provides insights into past ecological systems. Biofacies can reveal variations in sedimentary environments and are crucial for reconstructing ancient ecosystems and understanding biostratigraphy.
Body Fossils: Body fossils are the preserved remains of the actual organisms themselves, such as bones, teeth, shells, and other hard parts that provide direct evidence of past life. These fossils form a crucial connection to understanding the types of fossilization processes that occur when an organism dies and is buried, as well as the various environmental factors at play during biostratinomy and how these factors influence the quality of the fossil record. Furthermore, body fossils can undergo various forms of distortion and alteration, impacting their appearance and composition over time.
Correlation: Correlation is a statistical measure that describes the extent to which two variables change together, indicating whether an increase or decrease in one variable corresponds to an increase or decrease in another. In the context of geological and paleontological studies, correlation is crucial for establishing relationships between rock layers or fossil occurrences, helping scientists understand the chronological sequence and environmental conditions during different periods.
Cretaceous: The Cretaceous is a geologic period that lasted from approximately 145 to 66 million years ago, marking the final era of the Mesozoic Era. It is notable for significant geological, climatic, and biological changes, including the diversification of dinosaurs, marine reptiles, and the appearance of early flowering plants, which collectively shaped Earth's ecosystems.
Deposition: Deposition is the geological process where sediments, soil, and rocks are added to a landform or land mass. It typically occurs when agents of erosion, such as water, wind, or ice, lose their energy and drop the particles they have been carrying. This process is crucial in understanding how sedimentary layers form over time and helps to reveal the history of life through fossilization.
Diagenesis: Diagenesis refers to the physical and chemical processes that occur in sediments after their deposition and during their transformation into sedimentary rock. This term encompasses various changes such as compaction, cementation, and lithification, which can significantly influence the characteristics of the resulting rock. Understanding diagenesis is crucial because it connects sedimentary processes to fossil preservation, biostratinomy, and the overall geological context of terrestrial environments.
Facies Analysis: Facies analysis is the study of different sedimentary facies, which are distinctive bodies of sediment characterized by specific physical, chemical, and biological properties. This analysis helps in interpreting the depositional environments of sediments and is crucial in understanding the geological history of an area. It also plays a significant role in biostratinomy by examining how organisms, their remains, and other sediments interact after deposition, ultimately influencing fossil preservation and distribution.
Fossil Succession: Fossil succession is the principle that layers of sedimentary rock contain fossils that follow a specific order, allowing geologists and paleontologists to determine the relative ages of rocks and the organisms within them. This concept helps scientists understand the history of life on Earth and the progression of different species over time, revealing patterns in biodiversity and extinction events.
Ichnology: Ichnology is the study of trace fossils, which are geological records of biological activity. This includes tracks, burrows, and other markings left behind by organisms. Understanding ichnology is crucial as it provides insights into the behavior, movement, and interactions of ancient organisms, linking it to fossilization processes, sedimentary environments, and stratigraphic correlations.
Marine: The term 'marine' refers to anything related to the ocean or sea, including organisms, ecosystems, and geological features. In the context of biostratinomy, understanding marine environments is crucial because they are significant sites for the preservation and fossilization of organisms, impacting how we interpret the geological record. Marine settings influence sedimentation processes, which ultimately affect the biostratigraphic distribution of fossils.
Morphology: Morphology is the branch of biology that studies the form and structure of organisms, including their external and internal features. In paleontology, morphology is crucial for identifying and classifying fossilized remains, helping to understand evolutionary relationships and ecological adaptations. By analyzing morphology, scientists can reconstruct ancient life forms and gain insights into their behavior and environmental interactions.
Paleoecology: Paleoecology is the study of ancient ecosystems and the relationships between organisms and their environments over geological time. It helps scientists understand how past climates, biotic interactions, and geological processes shaped the distribution and evolution of life on Earth, linking it to various periods and events in Earth’s history.
Paleozoic: The Paleozoic is a major era in the geologic time scale that lasted from approximately 541 to 252 million years ago, marked by significant developments in the history of life on Earth, including the emergence and diversification of many marine organisms, early terrestrial plants, and amphibians. This era is essential for understanding evolutionary processes, major environmental changes, and the foundations of modern ecosystems.
Stratigraphic Column: A stratigraphic column is a visual representation of the layers of rock (strata) that make up the Earth's crust, illustrating the vertical sequence and distribution of these layers over time. This tool is essential for understanding the geological history of a region and helps geologists and paleontologists interpret the relative ages of rock formations and the fossils they contain, providing insights into past environments and biological evolution.
Taphonomy: Taphonomy is the study of how organisms decay and become fossilized, covering all processes from the moment of death to the discovery of the fossil. This includes understanding how environmental factors, biological activity, and geological processes affect preservation. The insights gained from taphonomy help paleontologists decipher the conditions under which fossils were formed and provide context for interpreting past ecosystems.
Terrestrial: The term terrestrial refers to anything related to the land or earth, particularly in contrast to aquatic or aerial environments. In paleontology, it often describes organisms or ecosystems that are primarily associated with land environments, influencing how we interpret fossil evidence and reconstruct past habitats and climates.
Trace fossils: Trace fossils are geological records of biological activity that provide evidence of the behavior, movement, and activities of organisms rather than their physical remains. They include footprints, burrows, feces, and feeding marks, showcasing how ancient life interacted with its environment. Understanding trace fossils is essential for reconstructing past ecosystems and connecting various aspects of fossilization, preservation, distortion, dating, and evolutionary biology.
Transport: Transport refers to the process of moving sediment and biological materials from one location to another through various agents like water, wind, or ice. This movement plays a crucial role in shaping sedimentary environments and influences the fossilization potential of organisms by determining where and how they may be buried after death.