What Makes a Fossil?

“We’ve long been concerned with the quality of the fossil record,” says Arnie Miller. “The key to all this of course is the available fossil record.” Miller points out that the most prominent issue is that the record gets larger and easier to sample the closer one gets to the present day in the Cenozoic Era. Therefore, we’ve long been concerned that global diversity curves, which show a big increase toward the present day, are biased.

“The rock is less hard,” Miller notes. “For example, on the Virginia Coast in sediments that are only a few tens of millions of years old, you don’t need a hammer, you need a sieve. Around Cincinnati, where the rocks preserve exquisite fossils that are more than 450 million years old, jackhammers and backhoes are sometimes helpful.”

Miller also emphasizes the subtle difference between samples taken around the world versus literature published from around the world. That is, not every sample taken is subsequently described in the literature. So in examining fossils and analyzing them, there are several inherent challenges, some natural and some under human control:

• Environmental

• How preserved

• Ecological

• Nature of the rock itself

• Duration of sampling

• Number of samples

• Number of articles published

“The nature of communities changes over time — how do you tally and correct for that?” says Miller. “And we’re trying to correct for all of them, basically.”

“Therefore, we have asked, ‘Can we quantitatively correct for the differences in sampling from interval to interval?’” Miller says. “Operationally, this involves some fairly arcane quantitative methods that, at heart, have a very simple goal: to quantitatively equalize the size of the paleontological sample from interval to interval throughout the geological record, so that we can build a new diversity curve that is free of the distortion that changes in sampling inevitably impart.”