Two Paleontologists Modeled the History of Fossil Hunting to Find Its Limits

Every fossil dig is a bet placed on a piece of ground. A team reads the geology, raises the money, spends a season in the sun, and only afterward learns whether that rock had anything left to say. Two paleontologists have now tried to settle part of that bet in advance, for the whole planet at once, by asking where there is still anything to find.

Thomas A. Neubauer of the Bavarian State Collection for Palaeontology and Geology in Munich and Mathias Harzhauser of the Natural History Museum Vienna report in Science Advances, published Sept. 23, that across most of the past 540 million years the honest answer is: very little. Their subject is one slice of the record rather than all of it: the animals that lived in shallow seas, not life on land and not plants.

They built the analysis out of two public archives. Fossil occurrences came from the Paleobiology Database, the main open collection of published fossil finds, and the geology came from Macrostrat, which tracks where rock of each age lies today. The Vienna museum's account of the work describes cutting the globe into equal hexagons and rolling the continents back to their positions in each interval, so that each site is judged against the seafloor it actually belonged to. For every cell, the pair then measured something less obvious than presence or absence: how fast collecting there has kept yielding new information over the decades and centuries it has been under way.

Those sampling histories flatten. Neubauer and Harzhauser report that for most time intervals, future data accumulation is expected to be negligible, and that geographic coverage is approaching saturation, the point at which new places stop appearing. Both are forecasts drawn from the shape of the fitted curves rather than counts of what remains in the ground, and a curve like that depends on the mathematical form chosen for it.

The qualifier in that sentence is where the story gets concrete. Both institutions' announcements name the ages, and the Munich release sets out the split: the Paleozoic and the earlier Mesozoic, the older part of the span, are the thoroughly worked intervals, and there the pair expect no meaningful gain in the near future. The Vienna release adds that work on those ages appears to keep returning to ground that is already well studied. The thinnest coverage is in the youngest rock: shallow-water deposits of the Cenozoic, the era that began 66 million years ago, are the least explored of all, even though a great deal has already been collected from them.

The other half of the work is a map of what is left. For the intervals where potential remains, the two reconstructed the present-day extent of rock that is both unsearched and geologically accessible: ground a field party could actually walk onto, rather than layers sealed under younger sediment or lying beneath the ocean. The authors describe the output as spatially explicit guidance on where undetected fossil information is most likely to be waiting, which matters because excavation is slow and expensive, and a season spent in the wrong valley is a season gone.

The maps carry a second kind of blank, and it is the one that surprised the authors. "We were surprised how large the areas are from which no information at all is available," Harzhauser said in the Vienna release, translated from German. Some of those blanks are simply unvisited. Others can never be filled: "From many regions we will never be able to collect data, because no deposits have been preserved here." Where the rock never formed, or formed and was later destroyed, no field campaign can produce a fossil, and Harzhauser calls those insurmountable limits on the growth of knowledge.

The paper's closing claim is practical: the results are a quantitative roadmap for prioritizing fieldwork, completing the databases of fossil occurrences, and bringing unpublished museum collections into use. It puts no order on the three. The Munich release makes the museum half concrete, with Neubauer noting that the same prioritizing applies to collections already in drawers and still waiting to be worked through. "That many regions of the Earth are still unexplored gives hope of exciting new discoveries," he said in the Vienna release, "so our maps are a kind of signpost for future research projects and a guide for funding bodies."

The authors' own opening line is the measured version of all this: the record is inherently incomplete, yet its physical limits "remain largely uncharted." What the two have charted is not the contents of the record but its edges, and the finding has two halves: for most intervals, more digging is projected to add little, and where it would add something, there is now a map.