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A paleontologist who coauthored experiments on soft-tissue fossilization, testing how mineral preservation can retain structures that would otherwise decay.^[ref]

A paleontologist who investigated taphonomy through experiments on soft-tissue fossilization, connecting observable decay and mineralization to exceptional preservation.^[ref]

A fossil is preserved evidence of past life in a geological context. A body fossil retains evidence of an organism's body, such as a tooth, bone or leaf; a trace fossil, such as a footprint or burrow, records activity. Complete replacement by minerals is not required for something to be a fossil.^[ref]

Fossilization can preserve different kinds of information. Permineralization fills spaces in biological material with minerals, while an impression may retain only external shape. These pathways help explain why the fossil record samples some anatomy characters much better than others, and why a transitional fossil is assessed through a combination of characters rather than overall resemblance.

taphonomy studies the transformation of biological remains from death or production into the material ultimately recovered and interpreted. It explains how a living organism or community becomes an incomplete geological sample. For shed structures or trace fossils, production of the evidence need not involve the death of the producer. Its relevance therefore extends beyond asking whether a skeleton was buried intact.

Three primary process classes are decay; physical disarticulation and transport; and burial alteration, including diagenetic mineralization. The boundaries are operational and the mechanisms interact: post-mortem decay can continue after burial, and previously buried remains can be reworked and transported again. biostratinomy groups events before final burial, whereas diagenesis groups subsequent physical and chemical changes. Those are stages or settings, rather than three mutually exclusive mechanisms.

First, post-mortem decay transforms tissues by autolysis, microbial decomposition and associated chemical reactions. Soft tissues, connective tissues and different phylogenetic characters disappear at different rates. The important result is not simply that hard parts survive longer: a partly decayed organism can acquire a misleading anatomical combination. Experiments on amphioxus and lamprey larvae followed recognizable characters through decomposition. Derived diagnostic features tended to disappear before some more general chordate features, producing a directional bias. Coding every unobserved diagnostic character as ancestrally absent can push a genuinely derived fossil toward an earlier position on a phylogenetic tree, the effect called stemward slippage.^[ref]

Experiments on adult hagfish and lampreys extended the comparison beyond larvae. They documented transformations as well as disappearance, so a residual stain or collapsed structure should not automatically be identified as an intact organ. Replicate specimens sampled through time are needed because destructive observations cannot follow every internal character in the same individual. For a new experimental test, temperature, water chemistry, microbial conditions and starting condition should be recorded and, where tested, varied independently. A laboratory sequence supplies constraints on interpretations; it is not a universal clock assigning an exact post-mortem duration to every fossil.^[ref]

Second, disarticulation, fragmentation and taphonomic transport alter which elements occur together and where they accumulate. Loss of ligaments releases bones, while currents or scavengers can move them. Shape, density, size, articulation and orientation influence transportability, so a concentration of robust elements need not represent the most abundant living species or the original place of death. Flow experiments and comparison of element representation, as developed in Michael R. Voorhies's vertebrate assemblage study, provide a basis for testing such alternatives. A useful comparison measures elements under specified flow and sediment conditions, with articulated versus disarticulated material distinguished. hydraulic sorting cannot be transferred unchanged between all animals and environments.^[ref]

The consequences include mixing habitats and ages. An apparently coherent bone bed may combine local and transported animals; reworking of fossils can place older remains in younger sediment; time averaging can combine successive communities into one assemblage. None implies that every fossil assemblage is hopelessly mixed. Articulation, abrasion, orientation, size distributions, sedimentary context and independent age information can instead delimit the plausible history. Abrasion alone is an imperfect transport-distance meter because material properties and the transport medium also matter.

Third, burial changes both preservation and geometry. Rapid isolation can reduce scavenging, but burial does not halt all decomposition. sedimentary compaction flattens and fractures remains; dissolution removes mineralized tissues; precipitation can infill pores or replicate tissues; fossil recrystallization can erase original microscopic detail. A fossil can therefore retain an excellent outline but lack its original chemistry, or preserve histology while its overall shape has been distorted. Mineralized replacement is not the only route to fossilization, and surviving original hard parts need not have undergone complete replacement.

Experiments by Derek E. G. Briggs and Amanda J. Kear illustrate constructive as well as destructive diagenesis. Decaying shrimps developed diagenetic mineralization by calcium phosphate preserving muscle detail, particularly in oxygen-restricted systems, with the animal itself supplying phosphate. diagenetic mineralization began on a timescale of weeks. This demonstrates a mechanism by which decay-associated chemistry can stabilize fine structures before they disappear. It does not show that low oxygen guarantees preservation: chemical availability, acidity, tissue composition and the relative rates of destruction and precipitation still control the outcome.^[ref]

These mechanisms are indispensable for reconstructing the history of life. A fossil's first occurrence is a minimum observation of a lineage, not automatically its evolutionary origin. A sudden appearance of soft-bodied organisms can reflect a new window of exceptional preservation, while disappearance of a phylogenetic character can reflect its destruction rather than evolutionary loss. Relative fossil abundance reflects both biological abundance and the probabilities of production, preservation, exposure and recovery. Comparisons of diversity through time must therefore consider changes in environments, preservational pathways and sampling. The fossil record is filtered evidence whose reliability can be tested; taphonomy identifies which biological conclusions that evidence can support.

Permineralization preserves biological material when minerals precipitate in its pores or internal spaces. Filling spaces in wood or bone can support and retain details of the original cellular architecture. This differs from replacing the original substance with a new mineral, although both processes can occur in one fossil.

Experiments placing wood in silica-bearing hot-spring water documented deposition of silica within the spaces of the tissue. Such observations connect a recognizable fossilization mechanism to mineral-bearing water entering a porous biological structure.^[ref] The speed observed in one chemical environment is not a universal clock for permineralization; composition, fluid access and subsequent alteration differ among deposits.