When I was college freshman, I was incredibly lucky to get a work study job with Niles Eldredge at the American Museum of Natural History. At the time he was studying a Devonian horseshoe crab and had heard from friends that modern ones were spawning at a beach in Staten Island. So my task for him was to head out there and bring one back. After a ride on the State Island Ferry, I reached the beach. All I could find was single dead individual, that turned out to be a gravid female. Taking it back on the subway to the museum, I realized how bad it smelled; so bad that I ended up with most of the car to myself (the smell was pretty remarkable even for the NYC subway in the 1970’s!). This was my first introduction to the stench of decaying marine animals.
Some years later, not long after I got my PhD, I was at the Friday Harbor Laboratory on San Juan Island in Washington. Based on a suggestion by Robert Aller (one of my committee members), I was studying the decay of shrimp in small jars containing sediment. I would periodically open the jars to track the rotting of the shrimp. By the end of the second week, the smell was so foul that my lab mates sent me of the end of the nearby dock to do my checking.
Why was I so interested in decay? I was investigating one of the fundamental questions of paleontology: how well does the fossil record preserve the once living world? Or to put in another way, what is the fidelity of the preserved signal compared to the original biological signal? The subdiscipline of paleontology that studies the processes and results of fossilization is taphonomy, literally the laws of burial.
As summarized in 1985 by my colleagues Kay Behrensmeyer and Susan Kidwell, we can break the stages of fossil preservation into three phases: necrolysis, the death of the organism; biostratinomy, from death to burial; and diagenesis, the time after burial. At each stage the remains can be totally destroyed, leaving no record, or can be altered by a range of biological, chemical, and physical processes. In terms of biological signal, these processes are the filters that alter it. My rotten shrimp studies were an attempt to experimentally examine the early stages in this process. Numerous recent and far more sophisticated studies by others have detailed the chemical and biological processes that occur after death and their impact on the formation of fossils. Yes, paleontology can be an experimental science!
An important take home message of taphonomic research is that every step in the fossilization is not simply loss of information; instead each phase actually adds critical evidence. How did the organism die? Who scavenged it and which bacterial decay processes were operating? What was the environment it was buried in? How much time does the fossil deposit represent? Etc. Rather than being viewed only as a bias or distortion of the biological signal, taphonomic processes have their own signal that we can use to aid our understanding.
These preservational signals can change over time. For example, a mode of fossil preservation labeled “Burgess Shale Type” (BST) which preserves soft-bodied marine organisms, is common in the Cambrian but essentially disappears afterwards. The window of time during which BST deposits occur reflect an exceptional combination of biological and environmental factors during that period of Earth history. Other periods of time are likewise characterized by conditions that are unique to them and that are reflected in nature of fossil preservation. Taphonomy thus has become part of the larger effort to understand the evolution of the Earth system over time.
The recognition of that fossilization is not simply “bias” is part of a welcome attitudinal change among my fellow paleontologists. We no longer shuffle our feet and apologize for what Darwin famously called “the imperfection of the fossil record,” leading to the impression that the fossil record is hopelessly incomplete and biased. In reality, that is very far from the truth. We now affirm that the fossil record actually contains a great deal of information, much of which is unique to it. As Steve Holland put it in his 2016 Presidential Address to the Paleontological Society, “As paleontologists, we have an extraordinary data set at our disposal, and we have the expertise to understand it. We have something that no other field of biology has — time, deep time….” As Holland said, there is a robust structure to the fossil record that allows testing of sophisticated hypotheses about the history of life. Our understanding of taphonomy promotes, rather than inhibits the framing of these hypotheses.