Right. You want to know what happens in the messy interval between the final breath and being buried under a pile of rock. Don't say I never give you anything.

Study of post-mortem–pre-burial tissue decay

A diagram attempting to impose order on chaos. It shows the messy handover from paleoecology and necrology (green) to biostratinomy (yellow), and finally to fossildiagenesis (orange). Nature, you'll find, rarely consults charts. [1]

Biostratinomy is the grim science of documenting the processes that dismantle an organism after it has expired but before it achieves the minor geological mercy of final burial. Think of it as the universe’s unsentimental recycling program. It is a critical subsection of the broader, and equally cheerful, science of taphonomy, which chronicles the entire journey from living thing to silent stone. Biostratinomy is wedged between necrology—the clinical study of the organism's death, the how and why it ceased to be—and diagenesis, which covers all the subtle and profound chemical alterations that occur after the remains are finally buried and on their slow path to becoming a fossil.

These biostratinomic processes are, by their very nature, overwhelmingly destructive. They are a relentless assault on form and information, a chaotic disassembly crew composed of physical, chemical, and biological agents:

• Physical effects: This is the brute force stage. It’s not an exhaustive list, because the universe is endlessly creative in its methods of destruction, but it includes being transported by water or wind, tumbling bones until they are smooth and featureless; the outright breakage of skeletons from the force of waves or rockfalls; and exhumation, the indignity of being dug up by scavengers or erosion before you've even had a chance to settle.
• Chemical effects: This is the silent, insidious decay. It encompasses the earliest changes to the mineral composition of bones and shells, and the slow creep of oxidation. It’s the universe’s patient chemistry reclaiming its atoms, rusting the iron in blood and beginning the long transformation of organic matter into something more stable, more mineral.
• Biological effects: This is where it gets personal. It includes the microscopic work of decay by bacteria and fungi, the planet's tireless janitorial staff. It involves scavenging, the far more gruesome cleanup by larger animals that tear, crush, and scatter remains. Then there's bioturbation, the constant churning of sediment by other living things—worms, roots, burrowing creatures—that disturb, displace, and destroy your potential final resting place. Some remains suffer encrustation, where other organisms decide your corpse is prime real estate. And finally, boring, which is exactly what it sounds like: other life forms drilling holes directly into your bones and shell. Because of course they do.

Let's be perfectly clear: for the vast majority of organisms that have ever lived, this process ends in complete and utter annihilation. Biostratinomic destruction is brutally efficient. The universe doesn't award participation trophies. However, if some fragment, some remnant, manages to survive this gauntlet and reach the point of final burial, a fossil may eventually form. That is, unless the forces of diagenesis finish the job later.

Because these processes are so heavily influenced by the surrounding environment—water currents, sediment type, biological activity—a careful analysis of a fossil's biostratinomy can reveal a startling amount of information about the world it inhabited. A cracked bone tells a different story than one worn smooth by sand. The boundaries between these three disciplines within taphonomy are, naturally, a human conceit. Nature is messier. In a fascinating twist of biochemical irony, the very microbes responsible for decay can sometimes seal and preserve an organism by creating a mineralized tomb around it, a process known as autolithification. This is now understood to be a critical, and very early, event in the formation of many exceptionally preserved fossils. Since this mineralization often happens before burial, it blurs the line between a biostratinomic event and a diagenetic one.

To understand these ancient processes, some people get their hands dirty in the present. A school of investigation, subsisting largely in Germany, called aktuopaläontologie, attempts to unravel biostratinomic effects through direct experimentation and observation on organisms that haven't been dead for millions of years. It’s less morbid than it sounds. Mostly. William Schäfer's book, "Ecology and palaeoecology of marine environments," stands as a classic product of this kind of investigation. More recently, researchers like D.E.G. Briggs and his colleagues have conducted meticulous studies of decay. Their primary goal is to understand the profound and unusual halt to these destructive processes that is required for the exceptional preservation seen in world-famous fossil sites known as lagerstätten. They are, in essence, studying how to stop the unstoppable, to comprehend the freak conditions needed to preserve something as ephemeral as a feather or an eyeball for eons.