Since Dolf Seilacher coined the term Konservat-Lagerstätten in 1970, these deposits have migrated from the margins to the mainstream of paleontological research. With greater understanding of the controls on their occurrence, new examples of exceptional preservation continue to be discovered. They provide critical data for phylogenies and stratigraphic ranges. Together with molecular data, they calibrate the history of many infrequently preserved taxa. Ostracods, tiny crustaceans with a biomineralized carapace, illustrate the importance of recent discoveries in Konservat-Lagerstätten. The rare examples with fossilized appendages are preserved in a diversity of ways, organically or through authigenic mineralization. They confirm that ostracods were present at least by the late Ordovician, provide evidence of relationships obscured by the morphology of the routinely preserved valves, and extend the stratigraphic range of particular groups. They reveal extraordinary features of the soft-tissue anatomy of ostracods, including reproductive morphology and strategy. While other taxa would provide equally compelling examples of research progress, it is clear that the concept of exceptional preservation is expanding. Future discoveries and new analytical methods will match the reconstruction of coloration in feathered dinosaurs, for example, for unexpected novelty.

Silicification is the replacement of original skeletal material accomplished through the concurrent dissolution of calcium carbonate and precipitation of silica. The processes is aided by the nucleation of silica to organic matter which surrounds the mineral crystallites within the shell. Factors that control silicification are those that influence the dissolution/precipitation process: shell mineralogy, shell ultrastructure (and, therefore, surface area), the amount and location of organic matter, and the character of the enclosing matrix. Silicification, like all types of fossilization, can produce taphonomic biases: it is far more common in Paleozoic than younger deposits, is more likely to occur in organisms with low-magnesium calcite shells, in carbonate sediments, and in environments with elevated dissolved silica.

Authigenic pyrite preserves non-biomineralized tissues in the fossil record under exceptional circumstances. Diagenetic models and taphonomic experiments demonstrate that active, localized sulfate reduction in iron-rich pore waters results in a strong concentration gradient, which confines pyrite precipitation to decaying organic matter. The locus and timing of pyrite precipitation is also influenced by the original composition of the organic matter. In recent decades, new sites with three-dimensional pyritized soft tissues have been discovered, although the Hunsrück Slate (Devonian) and Beecher's Trilobite Bed (Ordovician), known since the late 1800s, remain the primary examples in terms of diversity, abundance, and quality of preservation. Sedimentological and geochemical analyses at these sites have shown that rapid burial in fine-grained, reworked sediments sets up the high iron, low organic carbon conditions necessary for soft-tissue pyritization. Soft-tissue pyritization may also occur in association with other taphonomic modes, in particular with Burgess Shale-type preservation and carbonaceous preservation in lakes, although many of these specimens are now weathered. Continued comparison among sites and between specimens with variable degrees of preservation could help clarify the limits to soft-tissue pyritization and its distribution in ancient sediments.

This paper addresses the taphonomic processes responsible for fossil preservation in calcium phosphate, or phosphatization. Aside from silicification and rarer examples of carbonaceous compression, phosphatization is the only taphonomic mode claimed to preserve putative subcellular structures. Because this fossilization window can record such valuable information, a comprehensive understanding of its patterns of occurrence and the geochemical processes involved in the replication of soft tissues are critical endeavors. Fossil phosphatization was most abundant during the latest Neoproterozoic through the early Paleozoic, coinciding with the decline of non-pelletal phosphorite deposits. Its temporal abundance during this timeframe makes it a particularly valuable window for the study of early animal evolution. Several occurrences of phosphatization from the Ediacaran through the Permian Period, including Doushantuo-type preservation of embryo-like fossils and acritarchs, phosphatized gut tracts within Burgess Shale-type carbonaceous compressions, Orsten-type preservation of meiofaunas, and other cases from the later Paleozoic are reviewed. In addition, a comprehensive description of the geochemical controls of calcium phosphate precipitation from seawater is provided, with a focus on the rates of phosphate nucleation and growth, favorable nucleation substrates, and properties of substrate tissue and pore-fluid chemistry. It is hoped that the paleontological and geochemical summaries provided here offer a practical and valuable guide to the Neoproterozoic–Paleozoic phosphatization window.

Soft-tissue fossils are among the most striking and informative remains of extinct organisms. Although relatively rare, they are diverse, ranging from single microbial cells to nuclei and chromosomes; algae; metazoan embryos and larvae; flowers; complete, small, soft-bodied metazoans, metazoan tissues; integumentary structures such as melanosomes; skin texture, vertebrate feathers and hair, insect wings with color patterns, and sometimes even the entire bodies of large animals. The susceptibility of newly dead soft tissues to physical destruction, consumption, and microbial decay makes their preservation unlikely under most taphonomic conditions. In addition, their vulnerability to rapid autolysis, bioturbation, and destructive physical processes requires that rapid biological events must occur as the critical first steps of fossilization. An understanding of the processes by which biological remains enter the fossil record is important in inferring what non-microbial and microbial processes were operative in Lagerstätten. Paleontologists have recognized that microbial biofilms often accompany soft-tissue fossils, and have suggested that bacteria play an active role in soft tissue fossilization, but that role must be determined experimentally with living bacteria and dead tissue.

Marine embryos and marine bacteria are used to investigate the processes that mediate early steps in soft-tissue preservation because they offer simple systems for laboratory investigation of the roles of autolysis-blocking environments, microbial interactions, biofilm formation, and authigenic mineralization in taphonomy. Understanding microbially mediated preservation of embryos may supply new insights into a more general biology of fossilization.

The late Neoproterozoic witnessed a revolution in the history of life: the transition from a microbial world to the one known today. The enigmatic organisms of the Ediacaran hold the key to understanding the early evolution of metazoans and their ecology, and thus the basis of Phanerozoic life. Crucial to interpreting the information they divulge is a thorough understanding of their taphonomy: what is preserved, how it is preserved, and also what is not preserved. Fortunately, this Period is also recognized for its abundance of soft-tissue preservation, which is viewed through a wide variety of taphonomic windows. Some of these, such as pyritization and carbonaceous compression, are also present throughout the Phanerozoic, but the abundance and variety of moldic preservation of body fossils in siliciclastic settings is unique to the Ediacaran. In rare cases, one organism is preserved in several preservational styles which, in conjunction with an increased understanding of the taphonomic processes involved in each style, allow confident interpretations of aspects of the biology and ecology of the organisms preserved. Several groundbreaking advances in this field have been made since the 1990s, and have paved the way for increasingly thorough analyses and elegant interpretations.

Burgess Shale-type fossil assemblages provide a unique record of animal life in the immediate aftermath of the so-called “Cambrian explosion.” While most soft-bodied faunas in the rock record were conserved by mineral replication of soft tissues, Burgess Shale-type preservation involved the conservation of whole assemblages of soft-bodied animals as primary carbonaceous remains, often preserved in extraordinary anatomical detail. Burgess Shale-type preservation resulted from a combination of influences operating at both local and global scales that acted to drastically slow microbial degradation in the early burial environment, resulting in incomplete decomposition and the conservation of soft-bodied animals, many of which are otherwise unknown from the fossil record. While Burgess Shale-type fossil assemblages are primarily restricted to early and middle Cambrian strata (Series 2–3), their anomalous preservation is a pervasive phenomenon that occurs widely in mudstone successions deposited on multiple paleocontinents. Herein, circumstances that led to the preservation of Burgess Shale-type fossils in Cambrian strata worldwide are reviewed. A three-tiered rank classification of the more than 50 Burgess Shale-type deposits now known is proposed and is used to consider the hierarchy of controls that regulated the operation of Burgess Shale-type preservation in space and time, ultimately determining the total number of preserved taxa and the fidelity of preservation in each deposit. While Burgess Shale-type preservation is a unique taphonomic mode that ultimately was regulated by the influence of global seawater chemistry upon the early diagenetic environment, physical depositional (biostratinomic) controls are shown to have been critical in determining the total number of taxa preserved in fossil assemblages, and hence, in regulating many of the important differences among Burgess Shale-type deposits.

Carbonate concretions may preserve exceptional soft-tissue fossils. Organismal decay in sediment can produce HCO3− faster than it diffuses away, creating a local microenvironment of high alkalinity around the decaying organism that promotes carbonate precipitation. Infilling of sediment pore-space around the decaying organism decreases permeability and inhibits decay, thus increasing preservation potential within the concretion and promoting soft-tissue preservation. Different patterns of concretion growth may promote different mechanisms of soft-tissue preservation. Other factors such as shifting salinity and clay mineral chemistry, which increase preservation potential in the depositional environment, also promote soft tissue preservation within concretions. The rate of concretion nucleation and growth affects preservation; the faster concretions nucleate and grow, the better the preservation. Concretionary preservation is biased both by concretion-promoting environments and organism size effects on concretion formation.

The amber fossil record provides a distinctive, 320-million-year-old taphonomic mode documenting gymnosperm, and later, angiosperm, resin-producing taxa. Resins and their subfossil (copal) and fossilized (amber) equivalents are categorized into five classes of terpenoid, phenols, and other compounds, attributed to extant family-level taxa. Copious resin accumulations commencing during the early Cretaceous are explained by two hypotheses: 1) abundant resin production as a byproduct of plant secondary metabolism, and 2) induced and constitutive host defenses for warding off insect pest and pathogen attack through profuse resin production. Forestry research and fossil wood-boring damage support a causal relationship between resin production and pest attack. Five stages characterize taphonomic conversion of resin to amber: 1) Resin flows initially caused by biotic or abiotic plant-host trauma, then resin flowage results from sap pressure, resin viscosity, solar radiation, and fluctuating temperature; 2) entrapment of live and dead organisms, resulting in 3) entombment of organisms; then 4) movement of resin clumps to 5) a deposition site. This fivefold diagenetic process of amberization results in resin→copal→amber transformation from internal biological and chemical processes and external geological forces. Four phases characterize the amber record: a late Paleozoic Phase 1 begins resin production by cordaites and medullosans. A pre-mid-Cretaceous Mesozoic Phase 2 provides increased but still sparse accumulations of gymnosperm amber. Phase 3 begins in the mid-early Cretaceous with prolific amber accumulation likely caused by biotic effects of an associated fauna of sawflies, beetles, and pathogens. Resiniferous angiosperms emerge sporadically during the late Cretaceous, but promote Phase 4 through their Cenozoic expansion. Throughout Phases 3 and 4, the amber record of trophic interactions involves parasites, parasitoids, and perhaps transmission of diseases, such as malaria. Other recorded interactions are herbivory, predation, pollination, phoresy, and mimicry. In addition to litter, amber also captures microhabitats of wood and bark, large sporocarps, dung, carrion, phytotelmata, and resin substrates. These microhabitats are differentially represented; the primary taphonomic bias is size, and then the sedentary vs. wandering life habits of organisms. Organismic abundance from lekking, ant-refuse heaps, and pest outbreaks additionally contribute to bias. Various techniques are used to image and analyze amber, allowing assessment of: 1) ancient proteins; 2) phylogenetic reconstruction; 3) macroevolutionary patterns; and 4) paleobiogeographic distributions. Three major benefits result from study of amber fossil material, in contrast to three different benefits of compression-impression fossils.

Organic carbon compounds record key aspects of the processes of their formation and mechanisms of preservation and are foci for research into the nature of life on the early Earth and the search for life beyond Earth. Prime in this respect are lipids preserved in sediments and sedimentary rocks that reveal much about the evolutionary trajectory of life on our planet. Lipids, predominantly derived from photoautotrophic microbes, dominate hydrocarbon records in the Precambrian. The rise to prominence of the Metazoa in the late Neoproterozoic, metaphytes in the Paleozoic, and modern plankton in the Mesozoic, can also be seen in the occurrences of distinctive molecular fossils. Organic matter of all types is optimally preserved in environments and sediments where radiation (solar and ionizing) and oxygen are excluded. In the marine realm, anoxic water bodies will often become sulfidic (euxinic) due to the activity of sulfate-reducing bacteria. Phototropic sulfur bacteria thrive in such environments, and the presence of their characteristic carotenoid pigments goes hand-in-hand with the enhanced preservation of all organic matter, driven by the reducing power of sulfide. The deleterious effects of radiation and oxygen on the preservation of organic matter are amply demonstrated by the results of ongoing searches for carbon compounds on the surface of Mars. The production of highly oxidizing substances through radical chemistry operating in the Martian atmosphere has resulted in environmental conditions that virtually assure destruction of much of the organic matter produced in situ or carried there on meteorites and interplanetary dust particles.

The exceptional preservation of plant fossils falls into two categories: whole plant preservation and anatomical detail. Whole plant preservation is controlled primarily by transport and event preservation (e.g., ash falls), whereas anatomical preservation can occur through one of several taphonomic pathways: compression-impression, silicification, coal-ball formation, pyritization, and charcoalification. This review focuses on these taphonomic pathways, highlighting important factors and controls on the exceptional preservation of plants. Special emphasis is given to data garnered from experimental and actualistic approaches.

The exceptionally preserved fossil record of soft tissues sheds light on a wide range of evolutionary episodes from across geological history. Understanding how soft tissues become hard fossils is not a trivial process. A powerful tool in this context is experimentally derived decay data. By studying decay in a laboratory setting and on a laboratory timescale, an understanding of the processes and patterns underlying soft-tissue preservation can be achieved. The considerations and problems particular to experimental decay are explored here in terms of experimental aims, design, variables, and utility. Aims in this context can relate to either reconstruction of the processes of soft-tissue preservation, or to elucidation of the patterns of morphological transformation and data loss occurring during decay. Experimental design is discussed in terms of hypotheses and relevant variables: i.e., the subject organism being decayed (phylogeny, ontogeny, and history), the environment of decay (biological, chemical, and physical) and the outputs (how to measure decay). Variables and practical considerations are illustrated with reference to previous experiments. The principles behind application of experimentally derived decay data to the fossil record are illustrated with three case studies: the interpretation of fossil color, feasibility of fossil embryos, and phylogenetic bias in chordate preservation. A rich array of possibilities for further decay experiments exists and it is hoped that the methodologies outlined herein will provide guidance and a conceptual framework for future studies.

Knowledge of evolutionary history is based extensively on relatively rare fossils that preserve soft tissues. These fossils record a much greater proportion of anatomy than would be known solely from mineralized remains and provide key data for testing evolutionary hypotheses in deep time. Ironically, however, exceptionally preserved fossils are often among the most contentious because they are difficult to interpret. This is because their morphology has invariably been affected by the processes of decay and diagenesis, meaning that it is often difficult to distinguish preserved biology from artifacts introduced by these processes. Here we describe how a range of analytical techniques can be used to tease apart mineralization that preserves biological structures from unrelated geological mineralization phases. This approach involves using a series of X-ray, ion, electron and laser beam techniques to characterize the texture and chemistry of the different phases so that they can be differentiated in material that is difficult to interpret. This approach is demonstrated using a case study of its application to the study of fossils from the Ediacaran Doushantuo Biota.

Exceptional biotas—those in which the non-biomineralized tissues of organisms are preserved—are an important record of the evolutionary biology of the late Neoproterozoic—early Phanerozoic interval. Most of these biotas exhibit one of four modes of preservation: preservation of either 1) internal and external detail (Doushantuo-type preservation) or, 2) external cuticles (Orsten-type preservation) in calcium phosphate; 3) coating in pyrite films and infills (Beecher's Bed-type preservation); and 4) preservation of organic remains (Burgess Shale-type preservation). The global environmental and temporal distribution of each mode of preservation is reasonably well constrained, but not why these taphonomic windows existed when they did. The late Neoproterozoic – early Phanerozoic interval is characterized by complex, interlinked, physical, geochemical and biological changes to the Earth's biosphere and geosphere. The changing ecology of marine environments (from matground to mixgrounds: the ‘Agronomic Revolution’) occurred via an intermediate phase of stiffened, but not microbially bound sediments that extended the interval over which exceptional preservation occurred. Prolonged eustatic sea-level rise across flat-lying continental platforms ensured environments conducive to exceptional preservation were developed and, critically, sustained over large contiguous areas. During this, regolith on continental surfaces was recycled, providing an integral source of sediment and ions relevant to mineral authigenesis. Superimposed on these broad-scale changes are specific drivers that controlled the duration of individual taphonomic windows; elucidating these requires a better understanding of the environmental context and diagenetic history of fossiliferous successions at the intra-basinal scale.